Hacker News new | past | comments | ask | show | jobs | submit login
Big Bounce Simulations Challenge the Big Bang (quantamagazine.org)
127 points by SirLJ on Aug 20, 2020 | hide | past | favorite | 162 comments



I despise the big bounce because it's dogmatic in origin. "It makes sense that the universe just bounces instead of 'coming from nowhere'!"

Every time cosmologists looked, the universe got bigger and suggested growth. The big bounce at no point in history ever looked right. Moreover, the big bounce kicks the bucket down the road. It ultimately has the same metaphysical issues.

I find the reasoning poor as well. "I don't like inflation" != "The universe ends in contraction". Yes, it's proven difficult to explain CMB smoothness, but this doesn't mean the big bounce is a better candidate than other non-empirical ideas.

I'm confident truth will be far stranger than big bounce fiction.


On the other hand we have no direct evidence for Inflation and no idea what the Inflaton field is, what causes it or where it went. Yes I know the theory makes some predictions that have turned out to be correct, but if there are other theories that can also predict the same outcomes they deserve a hearing.

I don't think there's anything dogmatic about keeping an open mind. If you want to see dogma at work, see a reply to another comment of mine here where I'm ranted at about what is or isn't 'Scientific' and questions being 'non-scientific' simply for pointing out that the Big Bang isn't a complete model of the origin of the universe.

There are a lot of unanswered questions in this area and it's far from clear to me at least how they will be resolved, but I'm very excited to find out. I just don't think mud slinging about dogma and being non-scientific is going to help with that.


> Yes I know the theory makes some predictions that have turned out to be correct

However, I must say that once P. Steinhardt gave a seminar in my department, and he debunked two famous "predictions" of the inflationary theory (flat universe, scalar index n_s slightly less than ne) showing that papers published in the 90s claimed that inflation predicted "naturally" an open universe with a scalar index larger than one [1]. He used this to stress the fact that inflation can predict almost everything. I must say he sounded very convincing, he wasn't claiming that inflation is false, only that it is far from being a well-established theory, and that other hypotheses must be considered as well.

[1] http://physics.princeton.edu/~cosmo/sciam/index.html#facts


The metaphysical issues are unavoidable because whatever the theory we come up with or, I think, whatever the reality is, it can only fall within 2 possibilities:

- Infinity: There is no beginning and something always precedes the 'current' step (e.g. the Big Bang occurred out of something)

- Discontinuity: There is a beginning. Everything suddenly started out of nothing.

While both options are hard to grasp for the human mind, the second one, which is the standard Big Bang also sits very uncomfortably with Physics' concepts and is the more 'disturbing' of the two. I think that's why people have been looking for alternatives to the standard Big Bang theory.

Infinity, is still unfathomable but at least it is easier to fit Maths and Physics around.

Even adding God to the mix still leads to these 2 options, because if the Universe was created by 'God' it implies that the Big Bang is not the beginning and that something (God) pre-existed. The idea that we might be in a simulation is equivalent to a creator God, just more hi-tech.

It really seems to me that these alternatives, infinity or discontinuity, are inescapable.


Well, there's the Marvin Minsky answer. He believed that there is no difference between a possible universe and a real universe. Think of the difference between an algorithm that only exists in theory and running the algorithm on a computer. What do we add to the result by running it? We don't change the result, or grant it any greater validity in a metaphysical sense. The answer was always going to be the same and always will be the same. Minsky thought that our world is simply a possible world, but to suppose it is 'real' or not doesn't change anything and more than doing a calculation makes the result correct. It simply is.

It's similar in some ways to the concept of block time, in which there is no progression of time. The universe simply exists and the perception of the 'present' is an illusion. Similarly for Minsky the perception of reality or existence is an illusion.


> It's similar in some ways to the concept of block time, in which there is no progression of time. The universe simply exists and the perception of the 'present' is an illusion. Similarly for Minsky the perception of reality or existence is an illusion.

Labeling something an "illusion" like that seems like a massive cop-out, made by a mapmaker to avoid confronting the fact that their maps don't fully represent the territory. Fossils weren't illusions, and I don't think the present or existence are illusions either.


If a surgeon pokes your brain in the right place, that desk in front of you will disappear. You aren't experiencing reality directly, as per Plato's Cave. Reality seems precisely to be an illusion.


It isn't clear to me what you mean by "illusion". I generally interpret "illusion" to mean that things appear to be contrary to how they are. That is, an illusion is a way in which appearances are contrary to reality. But to say that "reality is an illusion", would then be to say that "reality is a way in which appearances are contrary to reality." . Which, appears to be nonsense.

I suppose if what you mean by "reality" is "perception", and if what you mean by "illusion" is also "perception", then what you mean by "reality" and "illusion" would be the same thing, namely, "perception", but, I don't think that's what you mean?


You choose the word "contrary" but a more accurate word is probably "different". The underlying nature that drives input to our senses is absolutely different from our day to day experience of three dimensional objects with distance. The underlying physical nature appears to be one of non-locality, and properties like shape and color are synthesized by your mind rather than inherent aspects of nature.

But even these models of an objective reality that come from quantum physics are not direct, as you had to build them in your mind through information you received through your senses, so this sense of an objective reality outside of your mind is also an illusion.


Well, what would it look like if the earth went around the sun instead of looking like the sun going around the earth?


They both go around each other.


The desk is still there, as confirmed by outside observers. If you are blind, is everything you touch non-existent?


How do you know about "outside observers" other than through a model you formed in your mind by data received through your senses? "Objective reality" is just another shadow on Plato's wall that can be extinguished.


Nihilism is neat until you realize it makes not testable predictions. So sure, everything could be totally an illusion and your brain is hooked up to a computer somewhere (or it is a computer). That’s a metaphysical claim that’s not falsifiable and doesn’t even make any useful predictions.

That’s not particularly relevant to a discussion about science and the Big Bang. In science we assume that multiple measurements by multiple people of the same phenomena gives us a good idea of the behavior and whether it matches our models. Our models will likely forever be incomplete but throwing our hands up in the air and trying to say “yes, but do we really know that” doesn’t seem helpful.


What if I am a few light-seconds away from the desk, so nobody "there" can confirm it exists "now"?


It’s a pleasing cognitive answer, but doesn’t really fit well with math or physics. Time is an emergent property of the Universe that we can measure and compare with a more platonic mathematical model of time. Also, you could make the argument that Minsky’s argument is just a form of discontinuity.


Greg Egan's earlier book Permutation City is a pretty interesting exploration of this concept in fiction.


Do you have a citation? I never heard of Minsky espousing this view. Could you be confusing him with Moravec? (https://frc.ri.cmu.edu/~hpm/project.archive/general.articles...)


Sure, he explains it here. All his interviews on Closer to Truth are worth watching, but then I'm a fan of the show. I don't know if the idea was original to him.

https://www.youtube.com/watch?v=PUbANEalnzc


Thanks, I'll also watch it later. It initially reminded me of Tegmark's levels of parallel universes (http://arxiv.org/abs/astro-ph/0302131) whose highest is one that assumes mathematical reality is the same as physical reality.


Thanks!


Wow cool thanks, I am reading about block time now. Weird thought, if time is a dimension, and the universe is inflating, could our perception of time advancing simple be a result of inflation in the time dimension?


> Infinity, is still unfathomable but at least it is easier to fit Maths and Physics around.

Arguably Maths requires this same discontinuity due to Gödel's Incompleteness Theorem. Consistent axiomatic systems require a Gödel sentence that is unprovable in the system; it requires a logical tautology or else your system will contain an infinite regress.

I think of a logical tautology as a kind of "something from nothing", but I suppose that is debatable. The implication of this property of axiomatic systems on reality is also debatable, but wouldn't any system we come up with to describe reality need to abide by these same rules?


> Consistent axiomatic systems require a Gödel sentence that is unprovable in the system; it requires a logical tautology or else your system will contain an infinite regress.

I don't see the connection between these two statements. Yes, in a consistent system with a finite description, a statement in that system which can be interpreted as "the system [description of the system] cannot prove [this statement]" cannot be proven (also, where "can be interpreted as" is taken to mean the sensible thing that it should mean) (though, sufficiently weak systems can have languages incapable of expressing such a statement) .

But the second part of that sentence, after the semicolon, appears to be talking about something else? It seems like it is describing the Münchhausen trilemma , except applied to mathematical proofs, and giving an argument that a system needs axioms (and/or rules of inference). While a system of proof does need axioms and rules of inference in order to conclude anything, this is not because of the incompleteness theorem.

The two do not seem particularly connected to me. So, I don't see why you connected the two statements with a semicolon.

Perhaps I misunderstood what you meant by the second statement in the sentence?

Also, when you say "logical tautology", are you talking about purely logical tautologies, or are you talking about axioms? The way you are using it makes it seem like you are talking about axioms, which I wouldn't call logical tautologies. But maybe you do mean what I would mean if I was to refer to "logical tautologies"? In that case, uh, I don't think logical tautologies are all that much of a foundation?


Gödel's theory relates to systems of mathematical proof (epistemology), rather than mathematical models of reality (ontology). The problem comes not with fitting maths around an infinite universe (which arguably requires fewer assumptions than for a finite one), but with building maths in the first place.


We need infinity in mathematics for proofs, limits, etc. Even magnitudes of infinity have useful properties in game theory, signal theory. There is something “real” about infinity that “works” in our Universe. The axioms of infinity in math seem to “work”. Could there be a better set of axioms? Sure, but no one has come up with any.


Yes, it’s silly to think the metaphysical issues would go away if we somehow proved the universe has been bouncing around for infinity amount of time.


You are correct. Although, I think the idea of the universe simply "bouncing around for infinity amount of time" lends a lot of otherwise unintuitive epistemological intuitions around ecological circuitry. There's a lot to be said to for how conceiving of things circuitously rather than linearly provides space for things which would otherwise end up elided.


Whether “adding God to the mix still leads to these options”, I suppose it depends on your philosophy/theology:

https://plato.stanford.edu/entries/eternity/#DiviTime

See also:

https://en.wikipedia.org/wiki/Eternity_of_the_world


I think discontinuity also doesn’t sit well with Math. What are the odds that we happen to be in a finite set? When you look at the axioms in first order logic the requirement of negation is suggestive of the idea that “nothingness” (i.e. something preceding a finite set) is a logical fallacy. It makes more sense, mathematically, to suggest that the current iteration of the universe is one step in an infinite set.


I don't think this makes sense. When you ask "What are the odds that we happen to be in a finite set?", what probability distribution are you talking about? It is entirely possible to describe a probability distribution over a finite set, and is, in fact, easier to do so than to describe a probability distribution over an infinite set. But, you said "happen to be in a finite set", which, seems to suggest that you are talking about a probability distribution over "what set we are in", where some of the sets are finite and some of them are infinite? If so, there is still the question of "what distribution are you talking about over sets?". If you are hoping for some kind of uniform distribution over sets, and arguing that "most" sets are infinite, then this is still fraught. Assuming ZF, there is an obvious correspondence between "Sets" and "Sets with exactly one element". Namely, [some set A] |-> [the set {A}] . You would have to define something like a measure or something?

Now, I don't mean to say that you can't define senses of talking about "most sets" or "how common are sets with a given property". I believe some people working with category theory stuff came up with a sense in which the "amount" of finite sets (up to bijection?) is Euler's constant, e. So, I don't mean that you can't come up with a sense of "most sets" in which it is true that "most sets are infinite" or even a sense in which "almost all sets are infinite".

But you would have to both describe the sense in which you mean that, and also argue for why we should consider that to apply to our intuitive notion of what is "likely" to be true of the universe in which we live, rather than some other sense.

Also, the universe having existed for a finite amount of time, doesn't really mean that the, what, set of points in time (in a given reference frame) is finite. Like, maybe time is discrete, but afaiu, we have never observed anything that strongly suggests that it is, and everything we've seen is compatible with using, and we usually do use, mathematical description of which are based on infinitely divisible time (though, there are some things about the planck time and whatnot.) . So, if time is infinitely divisible, the amount of points in time would be infinite, not finite. So, even if one successfully argued that it be "unlikely" that the set of points in time so far be finite, it doesn't seem clear that the amount of time so far shouldn't be finite, because the amount of points in time could be infinite in cardinality while being finite in measure.

Even if you wanted to argue that the cardinality of amount of points in time should be at least [any cardinality you want], I still don't think that would be a problem, because the class of Surreal Numbers have ordered subfields of arbitrarily large cardinality (as well as having arbitrarily large cardinality in any interval), and I don't think we could do anything to really distinguish between points in time being infinitely divisible and like the real numbers, vs infinitely divisible and like one of the larger subfields of the surreal numbers.

You would have to argue that it be unlikely that something like the measure of the collection of points in time so far be finite, not just something like the cardinality of the points in time.

_____

> When you look at the axioms in first order logic the requirement of negation is suggestive of the idea that “nothingness” (i.e. something preceding a finite set) is a logical fallacy.

I cannot get any reasonable meaning out of this. First order logic doesn't even have a concept of "finite"/"infinite" or "finite set". I'm pretty sure this is just nonsense. Having the universe of discourse be empty is a totally valid model of first order logic.

Also, I personally prefer to reserve the "fallacy" to mean "a step in an argument which is not valid", and therefore would not apply it to a concept.

Also, "something preceding a finite set" does not, in my mind, at all correspond to "nothingness", so I don't understand why you equated the two.


Are those really the only two options? Consider the surface of the sphere. It is not infinite in area, nor does it have a beginning or end.


How did the sphere come into existence?


If the "sphere" is 4D spacetime, including time, one might argue that asking what came before it is like asking what's south of the south pole.

The question of "why is there something rather than nothing?" is still absolutely valid, but my mind's open as to whether the answer necessarily involves either an infinity or a discontinuity.


To explain the existence of the universe you need to explain space, time, and energy/matter.

Even if you assume that space-time has always existed, an infinity scenario, (though you then have interesting questions on the nature of time if nothing exists) you still need to explain the existence of energy/matter, which will still be either an infinity or a discontinuity scenario.


Correct me if I’m wrong, but if time doesn’t exist you can’t violate the laws of thermodynamics, right? Would the existence of energy (which has mass) at T=0 not be a violation of a law that can’t exist until the clock starts?


Even Discontinuity implies that Nothing was there before Beginning, so it's same as "Infinity", but with legitimate excuse to refuse to study times before the Beginning.

Anyway, if Universe is infinite, it is infinite in all 4 dimensions. It cannot be infinite in just 1, 2, or 3 dimensions.


> The idea that we might be in a simulation is equivalent to a creator God, just more hi-tech.

Off topic, but I always found it interesting that some people who otherwise reject the idea of a God latch onto that one. At some point it's all kind of religion.


The Bible even combines the two:

God exists outside time and space (is infinite) and created the universe by calling a potential into form.

Which of course still has the issue of infinity: where did God come from? And even: what does it mean to not be limited by time and space.


IIRC 'eternal' used to imply both outside time and outside space; this was an everyday understanding 300 years ago, say.

According to this[1] 'eternal' is now ambiguous enough to suggest either "outside of time and space" or "persistent through all time."

On nested-simulation views I suppose it becomes necessary to clarify which clock domain(s) we are talking about, in terms of persistence or time.

[1] https://iep.utm.edu/god-time/


That is the thesis, is it not? The uncaused cause; /the/ axiom.


we have no evidence of anything yet, we have nothing yet to suggest that all the energy of the universe came into existence. Currently it seems like it is eternal. Big bang is just the point of inflation, it doesn't tell us much about before inflation, it starts with all the energy of the universe in a very condensed state.


I guess a 3rd option would be that the universe doesn't actually exist.


Genius! Someone tell r/noearthsociety


Is it not equally dogmatic to presume that the universe was nothing and then suddenly something and that nothingness is the natural resting state of experience and that before something-ness there exists nothing-ness?


> Every time cosmologists looked, the universe got bigger and suggested growth.

I mean... with the scale of the timelines being discussed, that makes sense.

They aren't suggesting that the expansion and contraction happens within thousands of years but billions of years.


That was my gut reaction too. Isn't this just saying "it's turtles all the way down"?


Has anything ever been observed coming into existence ex nihilo or does everything in existence appear to be reconfigurations of things already in existence?

"The universe" is not an answer because information about causal events prior to a configuration space capable of recurrent relationships is inherently unrecoverable not non-existent. (Unobservable =\= causally impotent.)


Well, our current particle theories predict that virtual particles constantly appear and disappear in a void, and we are actually building a huge laser to try to see if we can observe this happening.


> It makes sense that the universe just bounces instead of 'coming from nowhere'

This is why people are getting tired of scientism. Instead of being unbiased, some so called scientists are putting dogmas ahead of their observations and pushing for an agenda under the guise of science.


Both theories are somewhat incomprehensible for normal human beings. The idea, that everythinw we know just came into existence at some point is as shocking as trying to think of something that has no beginning and no end. We humans are inherently bad in dealing with these terms.


I'm not the physicist (my mother was), but as I understand it the 'came into existence' is not part of the big bang model.

Big bang only makes sense to a particular energy/time/space limit. All the energy that came to be all the universe already existed. What happened 'before that' doesn't even make sense. I was told that 'creation' type language is a misunderstanding of the big bang.

Is that not still the way it works?


The Big Bang theory itself doesn't answer the question of where the Universe came from, but I don't think it's stilly to ask what happened 'before' the Big Bang, or when the size of the Universe was near or below the Planck Scale. Relativity by itself predicts a singularity at a finite time in the past, at the beginning of the Big Bang. We know from Quantum Mechanics that Relativity is not complete though so the origin of the Universe and the nature of time through that process is still up in the air.


Scientific approach to the matter is actually simple: its scientifically impossible to research state before the big bang because no information from before original singularity is available. This makes question non-scientific.

We have wiggle room for planck epoch because that time was after singularity, meaning that we have information from that time (however little of it is left).

Closest we got to science here is by extending the time and space axis across the diagrams point of origin. This is where idea of singularity being in heart of higher level universe black hole (or past universe’s collapse) comes from. Its inpossible to verify black hole idea due to deletion of information, but collapse/crunch should be observable in distant future of the universe. Perhaps dark energy still has some tricks up its sleeve?


Roger Penrose disagrees, and it's possible he and some of his colleagues have identified circular features in the CMB which may have survived from a previous eon. The scientific approach is to keep an open mind.

https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology#Emp...


I truly dyslike when somebody uses that particular phrase, because it frames other participant as somehow close minded.

The fact that Penrose’s work is possible and ongoing is proof enough that scientific discourse on the matter is open and possible.


Well, you did try and close a door to a possibility. And you tried to frame that as being “scientific”. Yet, you cannot prove it.

Science never has final say on what’s impossible. Until (if ever) we have a grand unified theory that perfectly coheres all we find and ever find, you cannot claim to know of an impossibility.

For example, an easy proof you’re wrong would be simulation theories. In that case, the Big Bang is just a sub-simulation inside a bigger universe. Can you prove we aren’t in a simulation? If not, then you cannot make any claim about how it’s not scientific to talk about before the Big Bang. We just don’t know, so taking the positive is an error.


> Can you prove we aren’t in a simulation?

In context of scientific debate, no Simulation theory exists. Only hipothesis, and a very weak one, considered it’s not falsifiable. Hence its treatment as curiosity and thought experiment by scientific community.

Your hypothesis needs to meet some requirements in order to be scientifically viable to research. You cannot throw out scientific method out of window because it appears „close-minded” to you.

Until proof appears that singularity is not errasing information, scientific approach is to find a proof that there’s no singularity as threshold between old and new universe within a cycle. And argument for that is currently based on interpretation of some features pf cosmic background, which is scientifically debated.


There are definite ways to test for versions of simulations, but the point is thinking outside the box and then working your way back to scientific hypothesis you can test is the scientific process. You could make many testable predictions based on many different simulated universe hypothesis. Not to get even stuck on one example, my point was general that we cant know there aren't wildly unintuitive universe structures.


How can one speak of the size of the universe before the big bang if the concept of space-time was created during the event?


How do you know the concept of space-time was created during the event though? That's just an assertion. This theory, and the theory of conformal cyclic cosmology proposed by Roger Penrose do not have that feature, for example.


Size and progression do not require space or time.

The quantity of nodes in a branching tree of causal events can grow larger without time or space if there is no reccurance for any given state to be compared to another.

From the "gods eye view" the tree "grows" even if there's no internal information which can be used to recover any space/time prior to reccurance.


The idea, that everythinw we know just came into existence at some point is as shocking as trying to think of something that has no beginning and no end.

It's only an issue if you think about space and time as separate things. I find it makes (a little) more sense when you understand that time is a function of spacetime. Therefore if you're happy with space not existing prior to the big bang (which people do seem to be OK with) then automatically time didn't exist either, and hence 'before the big bang' ceases to be a problem.


This is what gets me. I can imagine no space and no time. But in a reality without space and time, by definition, nothing happens. There is nothing to act or be acted on. There is no timeline by which to order cause and effect. But the Big Bang posits that, in fact, something did happen: space and time began. The most incredible event imaginable occurred in the most impossible circumstance. It just doesn't compute for me. It's much easier for me to imagine that time is just turtles all the way down.


I feel it was just logic: nothing existed, but what is nothing? To define nothing you have to define what "something" is. So there should be something to allow the existence of nothing.


> The most incredible event imaginable occurred in the most impossible circumstance.

Think of time as "it prevents everything happening at once". Before there was time, nothing prevented everything happening at once, without space nothing prevented everything happening in the same place, so everything happened at once and in the same place. That everything happening made so much noise that it created space and time in a very big bang.


What is that "something" that is happening all at once? In my naive understanding of cosmological theories is they seem to end in probabilities (e.g., eternal inflation) that emerge from a kind of (oxymoronic) "chaotic static", but what does that mean for this to "happen all at once"? That statement seems to imply there's no degree of freedom through which something can occur (at least casually).

I suppose the question comes to, what is time? I imagine "time" to be a degree of freedom through which something can change. I understand some see time to be related to entropy, and that it's an emergent property of this thermodynamic property but this seems too limiting. It would seem entropy is more-so an explanation for the arrow of time, but not time itself.

If time is defined as the dimension through which something can change then should time not be fundamental to any cosmological theories that extends beyond the Big Bang?


> What is that "something" that is happening all at once?

Not "something". Everything. Like "What is possible to happen? Everything is possible". If you can't divide that possibility by time period, everything possible will happen with probability of 1. How improbable is that universe will happen during 1 trillion years? Very improbable. But if you can't tell in how many years universe will happen, it just will exist.

> but what does that mean for this to "happen all at once"

If you don't have time to make difference between two things happening one after another, they will happen both at the same exact "time".

> If time is defined as the dimension through which something can change then should time not be fundamental to any cosmological theories that extends beyond the Big Bang?

The problem is, time depends on local state of space. More energy/matter in a chunk of space means time is slower relative to other chunks of space. So when you try to go into past with mass in chunk of space increasing into infinity, that time notion breaks.


A series of causal events requires network reccurance for time to be calculable. If it's not calculable it can't be said to exist in any mathematical sense. So, a series of non-reccurent causal events at the fundamental level processes causally without the existence of time.

The same is true of "space" for the same reason. A causal network without reccurence (a tree) has no way to compare objects since there are no horizontal relations and it cannot "look" at backwards relations.

A non-reccurent causal tree has multiple instances of "here" and "now." But without anything to compare a given here/now to the concepts are internally meaningless.


That's actually helpful.


I can imagine no space and no time.

There is no timeline by which to order cause and effect.

I would argue that the second sentence implies the first isn't true. You can't imagine that there is no time if you're saying things can't happen without time. What I said doesn't mean things can't happen, it just means they happen in a way that doesn't require time to exist (which could be everything happening in the same irreducible instant, or in any order, etc.)


That's just a semantic dodge to avoid answering phrasings of the question that use the term 'before'. However the comment you're replying to didn't use the 'before' phrasing. We can't dodge the broader question of how, or why the Universe came about in the particular form that it did so easily.


You can dodge further by saying that causality only exists in space time, so asking what "caused" the start of space time is incoherent. But, "it just did" has never been a satisfactory answer outside the halls of churches and seminaries, so this dodge continues to be unsatisfying.


The phrasing is worded wrong here:

“it just did” has never been a satisfactory answer inside of churches or seminaries. That is why almost all the metaphysical discussion in these areas of human thought are around why we exist (in human terms).

“it just did” has been a satisfactory answer outside of churches or seminaries. This is why almost all discussion of why there is something rather than nothing in secular academia is ‘meh, impossible to know, don’t worry about it’


What I find shocking or, well, confusing, is the fact that things usually come into existence inside reality. Here we're talking about the coming into existence of something that it's easy to consider (I don't know how correctly) reality itself. How does that come out of nothing? And what even is nothing, outside reality?


Time as implemented in our current universe (which has counter intuitive properties, such a universal speed limit, which math does not require). It is possible that there is a version of time “before” the emergence of our physical “implementation” of space-time. There is no reason to stop assuming that the mathematical property of contingency doesn’t extend beyond the BigBang. Math is the foundation of Physics, not the other way around.


More concretely, a non-reccurent tree of causal events has both progression and various scales at consecutive slices of progression for an outside observer.

Intrinsically information about prior contingencies are unrecoverable "before" recurrence. But unrecoverable is not "non-existent."


But for all we know, time IS separate from space. Time is not like the 3 spatial coordinates in many physical systems. For example, Entropy increases with time, which doesn't make sense for a space-like property. Also, causality can be used to define a notion of past vs future even in 4D space time.


This makes intuitive sense to me, but isn't the issue that relativity states that time is intrinsically coupled with space? Ones experience of time relative to another's is directly related to the topological features of the space they're in. If it's more curved, time also "curves" and slows down relative to another observer in flatter space.

How does this notion of time become decoupled from space?

One way I imagine it is that "time" as a concept encapsulates at least two properties:

1) The degree of freedom (i.e., dimension) through which things can change; and 2) The unidirectional flow of causal events

Relativity seems more concerned with defining time in terms of casual events (e.g., event horizons) than its dimensionality. If we define "fundamental time" as a dimension that allows for change can it then be decoupled from space?


The core equation of special relativity that couples space with time is (assuming the speed of light is 1):

    ds^2 = dx^2 + dy^2 + dz^2 - dt^2
Different observerse disagree on what each individual term of the right hand side of the equation are; but every observers agrees on what ds^2 is.

Thinking in terms of 3 dimensional euclidean space, this makes sense. If you fix your 3 dimensional coordinate system and pick 2 points in space, you can have:

    ds^2 = dx^2 + dy^2 + dz^2
Another observer could pick a different orientation for their coordinate system, and arrive at different values for dx, dy, and dz; but they would still have the same ds. This is just the pythagorean theorem. The distance between two points is the same regardless of how you define your axis. This also means that your 3 spatial dimensions are inherently coupled; because there was no particular reason to pick your axis the way you did.

Simmilarly, in the 4 dimensional spacetime defined by the metric:

  ds^2 = dx^2 + dy^2 + dz^2 - dt^2
There is no particular reason to pick the particular time axis that you happened to pick. It is coupled with the other 3 dimensions in exactly the same way that the 3 dimensions are coupled in euclidean space.

The only complication here is that rotating your axis under the Lorentzian metric require the Lorentz transform; whereas rotating them under the Euclidean metric requires the Galilean transform.

The coupling described here involves no notion of causality. Nothing in the metric prevents a path from traveling in both directions along the time axis.


Well, even in this metric, there is an obvious separation between the 3 spacial dimensions and time. For example, a negative ds^2 indicates a fundamentally different kind of distance than a positive ds^2. In fact, events separated by positive distances would be considered entirely independent, while those separated by negative distances can have influenced each other; events for which ds^2 = 0 are simultaneous in any frame of reference.

Further, if two events have are separated by a negative ds^2, then all observers will agree on the order in which they happened, though they will not agree on the length of time that passed between them, or the relative positions.

Note that I'm using your version of the equation for the definition of ds^2 > or <0, though in general I've seen it expressed the other way around, ds^2 = dt^2 - (dx^2+dy^2+dz^2).


There is a clear assymetry between the temporal dimension and the spatial dimension; but it is not clear to me that this implies a seperation.

We can distances with ds^2 < 0 timelike, and ds^2 > 0 spacelike. We say that events with a spacelike cannot influence each other; but there is nothing in relativity that requires that (unless you introduce causality as an additional assumption, which we generally do).

This gets more messy in general relativity when you allow for large masses (read. Black holes).

In the case of a non spining black hole, we spacetime is described by the Schwarzschild metric. Expressing this metric in spherical cordinates, you find that when you pass the event horizon the sign of dt^2 and dr^2 flip, where r is distance from the singularity. This means a "timelike" seperation means that events are closer to each other in the time dimension; and events with a "spacelike" seperation are farther from each other in time. That is to say, "time" behaves in the way we think of as "space", and "space" behaves the way we think of as "time".


Time measurement is coupled to space, not time itself.

Actually, time does not exist. It's simply the rate of change of matter.


You're right of course but I find the cyclic version so much more intuitive.

The force from the big bang was imparted in an instant yet gravity is a constant force. IANAP but surely at some point the accumulative force of billions/trillions/... of years of gravity overcomes the force imparted by the big bang and the universe compresses into a singularity again?

I'd really appreciate someone explaining why this isn't obviously the case.


Gravity is traveling at the speed of light.

Space is expanding.

Objects far apart are traveling away from each faster than the speed of light. Or more that the space between them is expanding faster then the speed of light. So those objects will never have any sort of interaction.

Only ways around this if space itself start contracting. (No known way for this to happen).

Or somehow the universe is a big circle, and going far enough brings you back to the starting point. Negative curvature.

We don’t have any good theories on this. Some highly interesting ones that move the problem up a level.

For Example one theory is our entire universe is inside a black hole created from the remains of a four dimensional hyper star.

The math seems to work. Soo cool. But then where does the hyper star come from?

It’s “turtles all the way down”, is the thought to lot of the best theories.

Or everything is a simulation, again math kind of works. No direct evidence, but neat idea. But who’s hosting the sever that’s running the universe.

Something from nothing problem is a real trouble maker.


>Or everything is a simulation, again math kind of works. No direct evidence, but neat idea. But who’s hosting the sever that’s running the universe.

Its programmers all the way up!

But really, awhile ago I settled on the belief that its very possible we're in a natural simulation. Natural, as in, the same way that plants are simulations of L-Systems or in particular the same way my GPU once spat out cellular-automata-like behavior in a glitch.

If we are in a simulation, we've got no prior on what the world "above" us might be like. Oftentimes I see the theory shot down with "Our universe is too big and complex, theres no way any computer could be big enough to simulate it!" which is valid if assuming scale and physics anything like ours. But that's not a reasonable assumption here. It could be that the computational power of a cheap smartphone in the above world is similar to what a supercomputer the size of Jupiter or even Sun or any scale really for all we know. But that still assumes a programmer. If computing is done a lot in the above world at that sort of scale, our universe could be the result of a hardware glitch. That specific scenario may be quite unlikely, its just the extension of the GPU creating cellular automata by chance that I mentioned earlier. There's many other ways for algorithms of simulation to naturally emerge from reality just existing and things within it creating new sub-systems, which from within such a system, appear to be "something from nothing". So in a sense, it seems most likely that whatever the case is we are likely not one the "first layer" of reality, we are "simulated" within sub-layers. So then the interesting question is not how did this particular something come from nothing, but how can anything come from nothing, in the very first place, ever, at all? Once something exists, while scientifically we'd want an answer for how to get from there to here, its just a matter of what exact process that is.


Objects far apart may be traveling faster than the speed of light but once the universe reaches equilibrium won't there be intermediate masses that gravity will be able to travel through?

I was also under the impression that an expansion of space would just reduce the gradient of the gravity along that space and not inhibit its propagation.

If like a bubble space has some form of surface tension then would there be a point that it can no longer expand? Gravity could then become dominant and force the contraction. -edit-> I guess that wouldn't contract the space though just the matter?

I promise I'm not being pedantic or contrarian for the sake of it but to further my knowledge, thanks for your input!


There is no "equilibrium" the universe is moving towards, it is just expanding, and the "intermediate masses" are getting more spread out the more the universe expands. The expansion doesn't inhibit the propagation of gravity, it just makes the attraction between masses weaker and weaker the further they are apart, until they are so far apart that the space between them expands faster than the speed of light, at which moment they will no longer be able to interact with another, neither by light nor by gravity, and the contracting effect of gravity becomes weaker and weaker the larger the universe becomes.

According to out current best cosmological model, Lambda-CDM (which, admittedly, is mostly a phenomenological model for things we only half understand, but still describes our current observations better than any competing model), gravity used to be the dominant force in the universe when it was smaller so that the masses were closer together until quite recently. But now it looks like the expansion, the "Lambda" term in "Lambda-CDM", the cosmological constant of general relativity, has become the dominant force in the universe, and the universe is slated to expand ever faster.

It could start to contract if Lambda were closer to zero, but it currently doesn't look like it might move there. But then we don't know why Lambda it there at all and what causes it not to be zero in the first place, as everyone expected it to be until about two decades ago (Einstein himself thought of the introduction of the term into his theory as a blunder, as it would obviously be zero in any sane universe.)


> Only ways around this if space itself start contracting. (No known way for this to happen).

Maybe at the border of the universe there's a crunchy layer of mass that at some point gravity force will win over expansion.


Current estimate is that there is no border. It goes on forever.

Space is infinite and increasing.

Matter is fixed and static.

So a bigger infinity divided by a smaller infinity.

Which means density is heading towards 0. This is heat death of universe.

Now since dividing infinity by infinity is nonsense, this a sign our understanding is incomplete


The issue with this view is that in the universe we see today the gravitational force is not strong enough to do what you describe here. There is acceleration of the expansion i.e. energy is added to the system (in the form of vacuum energy possibly).

To say it in another way, the energy used to expand the universe today is not only the initial force imparted by the big bang but is added to as part of quantum processes in empty space. However as the universe expands, the amount of matter (dark + luminous) does not increase so the proportion of gravity/matter to dark energy (the force that accelerates the expansion) is getting lower and we get an acceleration.

These observations exclude the possibility of a "big crunch".

Disclaimer: I am a statistician not a cosmologist but this is how I have understood it.


Cheers, I now understand why it's not such a clear case. I fear I may have many more harder to answer questions now though - Thanks none the less!


Take the idea a little further, to the end of the universe, and the rate of acceleration of expansion of space increases so much that stars become isolated from each other, then planets from stars, then molecules from each other, then atoms, and then quarks, the constituents of matter itself, and then....

An interesting thing happens.

When you tear a quark away from it's antiquark, you get two quarks. The energy is equal to that required to bring another quark into existence. At this point, the rate of expansion is so vast that every quark in the universe has been forever isolated from one another, and then each bursts into a sea of high-energy quark-gluon plasma. The massive energy of expansion is rapidly consumed generating these quarks, and then the expansion slows, never stopping, but continues at a much slower rate.

Wait... we've seen this before. A quark-gluon plasma, rapidly expanding from a single point, in a universe isolated from all others.

Only expansion is required to generate new universes, forever.


I'm not sure we can ever tell the difference between the two models. Given the assumption that both produce a "boring" universe, and that models are never completely verifiable, it could be that either pathway appears the same to us at this point in time.


The Universe can be infinite without being cyclic.


Actually I find an absolute beginning and an absolute ending more troublesome to think about. It is easier to accept that in reality while everything keeps changing and recycling, the sum total has always been.


why there is something at all, i think we can never know. but yeah, likewise. it seems energy/things existing for infinity is the only thing that makes sense, and something coming from nothing is impossible. i think a part of us wants there to be a beginning but there really can't be.


On the other hand, maybe this bouncing is completely deterministic and we are meant to do the exact same things we did trillions of years ago.


If the universe has infinite bounces than yes, there are countless universes in the past and future where I type this same message.


“Why there is something at all?” The only answer I can satisfy myself with at least a bit is that there is no option for nothing to exist.


A circle doesn’t have a beginning or an end, yet folks seem to be okay dealing with them.

Personally, I’m stumbling on understanding physical fields. This looks like another field is being added, which is nice in some sense, but why do we have the number of fields that we do and what conditions are needed to create/sustain physical fields?


The issue is not that a circle has no beginning and end, but what led to the creation of the circle in the first place? It didn't materialize from nothingness, I drew it on a paper.


Rather than materialize from nothing, every event would be connected to the next and if you proceed along the events, you'll eventually see the same/similar events again. Sort of like a circularly linked list.


Except now you have a winding number and the two circles aren't equivalent everywhere.


Many comments here address an important issue: the human mind has a hard time making sense of both an eternally existing universe, as well as something-from-nothing. But most of the issues stem from presupposing physicalism. It's understood even by staunch physicalists that choosing this metaphysics is ultimately arbitrary[1].

There's another way to approach all this. Start by asking: what's the one thing I know for certain? It's hard to say any more than it certainly seems like something is happening. Investigate this sheer fact of "seeming." See what the seeming is like before you apply any metaphysics on top of it. What happens when you do this extremely precisely?

Suppose that the correct metaphysics is that you are ultimately the primordial ground of being, that (paradoxically) weaves itself into apparent realities. What we think of as physical reality is just one instance. It transcends parameters like time and causality, but can give rise to them of its own will. Being the primordial ground of being, nothing logically prevents you from knowing this ultimate truth directly and unequivocally (unlike if you were really just a human).

As it so happens, the preceding paragraph describes how you would (re)arrive at this knowing. Or at least, that's what's suggested by various mystical traditions. As far as I can tell, there's definitely something to it.

[1] "There is no way to distinguish between the scenarios by collecting new data. What we’re left with is our choice of prior credences. We’re allowed to pick priors however we want. [...] We have every right to give high credence to views of the world that are productive and fruitful." —Sean Carroll, The Big Picture (p.91)


I have never heard about Big Bounce before, honestly, but the illustration at the top of the article basically made sense in a heart beat and I'm impressed how simple yet how much of the idea it conveys, apparently, correctly. Kudos to the visual artist, usually these scientific illustrations used to explain a weird or novel idea are over the top.


I vaguely recall hearing of this from a different field of study.

https://www.cs.ubc.ca/~goyal/age_of_universe.php


Anyone else when they think about the origin of Universe for a long time, start to wonder how the hell do we even exist and get a feeling like a panic attack? I don't really know how to accurately describe the feeling. Its a very weird sensation. It only happens when I think about the origin of Universe. And its very very hard to arrive at that state. Requires a lot of concentration. I must have experienced it like less than 5 or 6 times in my life so far.


It is called existential anxiety, it shows that you are able to contemplate about your own insignificance in contrast to the grand scheme of things (universe, all of existence, etc.). We all have it on one level or another, I used to have it when looking into a dark cloudless night, realizing that all of the little dots I can see out there could technically be orbited by another planet that bears life, inhabited by millions or billions of other lifeforms that could be able to feel and think.

Usually it is nothing to worry about, except when you get obsessed by it and it starts to control aspects of your life because you build a worldview around it or try hard to avoid it or explain it away: then it is called an existential crisis. But what it really means is that the mind gets overwhelmed by the fact that the universe is orders of magnitudes more complex than what the self has ever encountered in our daily lifes. Our brains have evolved so that bipedal apes that migrated from forests into the steppes can survive and cooperate in groups. It was never meant to be confronted by questions of this dimension, but yet here we are.

You can make your peace with it, and embrace it. It can also be a source of endless curiosity, spirituality and creativity.


I remember learning the term "existential crisis" long before I ever experienced it. Then after floundering mentally for a long time, I suddenly connected the two, and the realization that so many other people throughout history have had the same exact feeling - so much so that there's a term for it which is almost a cliche - made me feel a lot better for some reason.

I decided to accept the Douglas Adams perspective: In an infinite universe, an infinite number of seemingly improbable things will inevitably happen, including a random number of particles ejected from astronomical explosions collecting together in one spot in such a way and for just enough time to create life as we know it, and for some of that life to think, "Why am I here?", before entropy rips all of it apart again a cosmic blink later. We exist because in an infinite universe, all things that can happen will happen, including you. There's even a universe in which a god did in fact create everything... which is an interesting question: How do we know if we're in that universe or not?



"Theoretically, over an extremely large but not infinite amount of time, by sheer chance atoms in a void could spontaneously come together in such a way as to assemble a functioning human brain."

That's fantastic.


It might be a bit preposterous to say what humans were meant to do or not to do, especially given that with a sample size of n = 1 we have humans actually wondering about such things.

Existential anxiety isn't per se about the relative size of self to the world but more about the inability to grasp and control the understanding of it. Pretty much everything living strives to "control" things, and in the case of human beings this applies to mental things too. Controlling things on a mental level is usually about understanding them, not necessarily about bending them to our will.

Anxiety is tied to a difficulty in dealing with perceived lack of control (over others, over our emotions, over the future..), and existential anxiety is an example of anxiety when it comes to existence. We simply don't know enough to say something that cements control.

Thankfully one of the coping mechanisms is humour, so I'll leave the reader with the very well known Douglas Adams bit:

“The story so far: In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move.”


The sentence you object to was not thought of as a teleological dogma of what humanity is meant to do or not, but an evolutionary perspective of why our brains are not very well equipped to handle some questions and/or scales of such dimensions (maybe it wasn't the most apt expression -- I am not a native English speaker). The sensory and processing equipment that has evolved by giving early hominids the advantage to use tools and language stumbles somehow when it is confronted with the vastness of the universe -- it loses track of the local reference frame...


Interesting. I’ve had the exact opposite reaction. At times when I’d suffer from anxiety my most effective remedy would be to sit down outside and observe the stars until that deep feeling of insignificance from really seeing it all presented itself.

Somehow the perspective of my life just being a tiny sparkle in the grand scheme of things would render any stress moot.


The feeling of insignificance is merely one possible response of a range of arbitrary emotional responses. It has been made more prevalent by a cultural, existentialist meme. I choose wonder and amazement as my arbitrary emotional response. It is more satisfying. I hope that whatever superintelligence we create will speak to us about the answers it finds to these questions, and not choose to wipe us out instead.

There is no reason that a superintelligent AI cannot do the following: create superintelligent theories about the universe (using superintelligent intuition), create superintelligent tools to prove its superintelligent theories, leading to superintelligent empirical observation, ultimately producing the answer to the question of our existence far faster and far more eloquently than is predicted.


Perhaps insignificant was a poor choice of word. Did not mean to imply that in an exclusive sense. Rather inclusive, a tiny tiny part of something inspiring, as you put it, wonder and amazement. And, I would add, to underline the inclusive part: pride.


What GP is describing is not quite existential anxiety..

Not the dread of an insignificant existence, rather, the dread of an unending existence.


I am dreaded by how reality works and there is no way to explain any of it. If the reality has no ending or begining, how does it operate? The reality does follow some rules. How is is it enforced? Where does the rules run? How are the rules defined?


I think the reaction to cosmological origins rather depends on how much you are trying to (implicitly) stay within your existing beliefs.

If you approach with a healthy nihilistic attitude, it's just cool stuff but doesn't matter(because nothing matters and as a nilhilist that's OK). But if you're chained to upholding or championing something, the existence question may become an enemy, one that is so hard to dismiss that it drains you.


Yes, I've had this happen several times as well, and only when thinking about the origin of the universe (or the origin of God, which is essentially the same thing). It doesn't seem to be a feeling I can create consciously, i.e. thinking about it right now doesn't cause it to happen.

I always wondered whether other people experienced this too, now I know. Thanks!


I experience that too, and only when I ponder the universe and ultimate questions like “why is there something rather than nothing?” It is a strange feeling that comes fast, some feeling of absurdity of it all mixed with the pain that we humans will maybe never be able to answer such questions, and it feels like a strange panic attack, felt both in the body and brain.

I take solace in some way that I am not alone in this and that there are other groups of trillions of atoms somewhere else in spacetime pondering the same questions with the same intensity.


I love / hate the sensation when you try to conceive that it (it including whatever includes "it", ad infinitum) has either existed forever or there was a point before anything existed.


For sure, I have experienced similar feelings. Good to know it's not just me. It's kind of like a derealization caused by the thought of how absurd or odd it is that we exist at all.


>Anyone else had the feeling where you think about the origin of Universe for a long time, it doesn't make any sense and you almost get a panic attack?

For whatever reason, it makes more more anxious than it should. The concepts involved are so far removed from my brain's understanding of reality that it makes me uncomfortable.


Yes. It feels like we're never going to escape, if there's no beginning.

Like you're about to touch something that could cause everything to blink out of existence.

It actually causes physical discomfort and an increased heartrate and rapid breathing, like you need to turn back, NOW.


I think of it as having an "existential crisis". Its not just limited to thinking about the universe for me, but things like eventual death and all those "impossible to understand" topics.


yes, i find it's a useful antidote to the existential fear of death


The universe always having always existed makes slightly more sense to me than it just popping out of nowhere. Sure, from the Big Bang onwards the inflation theory seemed to make sense but it didn’t explain how everything could magically erupt out of nothing or what caused said eruption when nothing existed prior to it. For all the crap that religions get for believing in nonsense, I always felt the Big Bang was a scientific parallel.


That's just our own minds applying their own adaptive heuristics to the universe, though. We're used to dealing with systems that have a history, because that's what allows us to avoid the tiger lurking in the dark. But there's no particular reason to think that kind of evolved thinking should be scale free, through time and space.

Why is a universe that has always been in existence, cycling through different states, any more sensible than one that pops into existence only to ultimately fizzle out? Both require the presupposition of some kind of uncaused system. Gathering evidence pointing toward one or the other is key.

I do think that the Big Bang maps better to Western religious cosmogony (matter was created ex nihilo) and Big Bounce to philosophical materialism (matter is the fundamental substrate of the world), but that shouldn't bias a scientist against the Big Bang.


In this territory, a lot of arguments of the form "This does seem to be the obvious conclusion based on our human thought ,but that is a mere delusion/illusion" - the implication is that someone has an ultra-insightful way to see through the illusion. They don't ; they just seek a little bit of self-edification and ego-stroking by suggesting as much. Arguments of that style are incredibly weak "It only VERY POWERFULLY SEEMS SO" is actually an admission that an unbiased person would reach the conclusion being rejected. The scientific community clung to the steady-state model of cosmology for nearly a century before embracing Big-Bang theory - this was due to philosophical attachments rather than any sort of evidence - these sorts of motivations are still at play today. They mocked and derided those who advanced alternatives until the evidence became so overwhelming that it could no longer be denied.


Kept scrolling, not sure what I was looking for. This was it, thanks for a great comment.


The way I'm put together, both ideas makes me uneasy when I _really_ think about them. There used to be no universe? Ugh :( There's always been an universe? How's that possible? Ugh :(


> For all the crap that religions get for believing in nonsense

Curiously, Latter Day Saints (aka Mormons) have taught for over a century that essentially the Big Bang theory is incorrect and that matter has always existed and that when the Earth was created God simply "organized" existing matter rather than conjuring something out of nothing.

Putting aside their other beliefs I thought this was an interesting curiosity in this context.


Yep- there is a reason there are so many Mormon sci-fi authors and why Mormons are one of the few religions where engagement increases with education.

Growing up LDS there was never any existential angst as I became more educated and there was never a need to overcome any cognitive dissonance as I learned evolution or cosmology- the baseline belief is a very sci-fi one of the first super-consciousness (God) taking upon itself the shaping of spiritual (dark matter?) and then physical matter and making pathways for other intelligences to master the same. No ex-nihilo involved.

Even if the LDS specific conceptions have all the details wrong, the overarching idea is completely plausible.


As Terence McKenna said: "Modern science is based on the principle: ‘Give us one free miracle and we’ll explain the rest.’"


Religion simply starts with the idea that what we observe is not meaningless. Reality is often stranger and more incomprehensible than fiction.


Does it change anything in your perception of “coming into existence from nothing” if the total energy of this universe is 0?


Sir Roger Penrose and Dr William Lane Craig had an interesting discussion[0] that included him talking about the Big Bounce (around the 50-minute mark).

[0] https://youtu.be/9wLtCqm72-Y


As I have long suspected, though computer science is a subset of mathematics, cosmology is actually a subset of computer science.


They're both variations on information theory.


This seems at least superficially similar to Roger Penrose's Conformal Cyclic Cosmology theory.

Anyone here able to weigh in on that?


There's some interesting theories about what was happening before the big bang in the Joe Rogan interview with Brian Greene https://youtu.be/FHAA_1Guxlo


It is also worth nothing that cyclic cosmogony was envisioned more than two millennia ago in Hinduism.

https://en.wikipedia.org/wiki/Hindu_cosmology


Most human questions about the origin of things assume that the default state must be Nothing.

Why can't it be Everything?

i.e., instead of imagining the Universe as a white dot on a black canvas, how about thinking of it as a black dot on a white background?


My biggest problem with the big bang is why didn't the incredible density of energy (it hadn't cooled enough for matter) just turn into a black hole?

The big bounce avoids this particular problem.


Inflationary theory. Someone more educated on the topic can pine in, but my lay understanding is that the output of some form of primeval radioactive decay (Big Bang) caused a phenomenal rate of spacial expansion, which caused space to expand faster than the rate of gravitational collapse in those first moments.


It's not the rate of gravitational collapse you have to beat, it's the speed of light.

Although I guess that makes sense. After all it's spacetime, not space. So if the expansion rate is higher than the speed of light, then you don't have the black hole problem.


The universe is and always was infinite even at the big bang. At the big bang although the universe was incredibly dense it was so uniform there was no net direction of gravity to cause clumping. That and inflation rapidly expanding away any quantum imperfections beyond causal contact.


Why does it avoid the problem?

> Over billions of years a contracting scale factor brings everything a bit closer, but not all the way down to a point. The dramatic change comes from the Hubble radius, which rushes in and eventually becomes microscopic

All the matter of universe at a microscopic radius? That doesn't avoid the problem.


There has to be spacetime to form a black hole, where would it find such spacetime before the big bang...


Well what about 0.000001 seconds after the big bang (add zeros as needed).


TL:DR; despite the title, mostly the theory challenges inflation (which itself was originally partly an attempt to answer predictive flaws with earlier cyclic theories) - the big bang itself is countered in so far as a "single point" state is not required.

With this continuous (eternal?) contraction and expansion, I'm reminded eerily of a heart beating, or something breathing...


I thought the universe is too big as to contract again?


The results don't necessarily tell us about the future- but that there may have been a bounce in the past.

As far as being too big, that's not quite it. Everything is moving away from each other because of the big bang, but astronomers realized that hey, gravity should be slowing that down. So they tried to measure the deceleration of the expansion of the universe. Instead they found it's accelerating.

There's a lot of theories as to why, but right now it's just called "Dark Energy" because no one really has a full understanding of it. Space itself seems to be stretching out, becoming larger.

Will the acceleration of expansion continue forever? Maybe someday it will slow and reverse? No one is sure yet.


The bing bang is way too accepted in the mainststream: in reality there is no concrete proof for it.

Therefore we can either: a) Fit the models to fit the data. b) Invent more physical phenomena to make it fit the data (quasi particles in physics).

There is nothing wrong in doing that, but there is severe arrogance of saying that "the bing bang happened" where in reality we just have a hypothesis.

And even "the most widely accepted by CONSENSUS" hyptothesis doesn't make mean is actually TRUE.

It's perfectly fine to make new theories, but at the end of the day we simply don't know enough: and yet the mainstream/every kid believes in the the bing bang to the extend as religous people believe in God.


There was very much a prediction of the Big Bang, before it was strongly supported by experimental evidence. This is what Penzias and Wilson got the Nobel prize for. Their accidental detection of the Cosmic Microwave Background matched a prediction by Gamow, and others previously, and it was also used as evidence to rule out solid state theory. Does that mean it's the whole story? Of course not necessarily, and the Big Bounce isn't necessarily incompatible with these observations. However, I don't think the idea that the universe rapidly expanded at some point in the past is under any doubt.

So this wasn't a model fitting the data. In fact it was an accidental observation which agreed with a model that had been suggested much earlier. The fact Penzias and Wilson weren't even looking for it makes it even more unbiased. Wilson, I believe, was also a solid state person (as were many prominent physicists in the 20s and 30s).


Do you mean "solid state" or "steady-state?"


Oops, yes, I meant steady-state! :)


It was my understanding that physicists have never claimed that the big bang happened. That the big bang itself isn’t really part of the theory at all and that its simply a singularity point, but that some moments before that point, ohysics as we know it breaks down, so we don’t know what happened before and therefore do ‘t know if there was a bang or not, just that after that time, things happened that we can measure. Put another way, the big bang theory doesn’t include the big bang itself (the something from nothing part) but is about the inflation and expansion of the universe.

Here are some PBS Space Time videos on the subject:

Why the big bang definitely happened: https://youtu.be/aPStj2ZuXug

Did time start at the big bang: https://youtu.be/K8gV05nS7mc

Whats wrong with the big bang theory: https://youtu.be/JDmKLXVFJzk

“In the beginning, there was nothing, which exploded”, now, a lot of non-scientists like to repeat this statement, but no credible scientist has ever said this, nor believes it. So its unfortunate that this statement is used to deride the big bang theory. The big bang describes a series of events that happened to the universe following its existence in an extremely hot, dense state. We have a ton of evidence that the universe was once in such a state. Perhaps our understanding of this state will eventually lead to a theory of the origin of the universe, but the big bang theory as it stands does not claim to explain such an origin. — Matt O’Dowd, PBS Space Time


The Big Bang theory was originally proposed by a Catholic priest (and mathematician, astronomer, physicist), Fr. Georges Lemaître:

https://en.wikipedia.org/wiki/Georges_Lema%C3%AEtre

He "initially call[ed] it the 'hypothesis of the primeval atom'."


I mean. Sure? This is how science works.

The "theory" of evolution is the same thing. We have no "proof" of it. But of course we do. Evidence is all around us, being evaluated in a multitude of ways by a multitude of people using different sources of data making similar conclusions supported by experiments and evidence. This is basically how we define "fact".

Of course somebody may stumble onto something that blows the whole equation up, but barring that, we have sufficient confidence to say it's fact. Granted the big bang theory is harder to observe, study, and experiment. Doesn't change how it's viewed by science.

(TFA opens with this. It suggests the possibility of something that may blow up the equation. Great. Similarly, if somebody can find something that disproves evolution that would be pretty ground-breaking, but the more established a fact, the higher the burden of proof.)




Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact

Search: