
Quantum Gravity’s Time Problem - CarolineW
https://www.quantamagazine.org/20161201-quantum-gravitys-time-problem/
======
abakker
I have a question as a non physics/math person:

We assume that light speed is a constant, but we also know that speed is
measured as distance/time. We know that in the presence of high gravity (or
proximity to very high mass), or very high speed, we experience time dilation,
and that perspective and location matters WRT actual time.

So, how do we assume that light speed is constant? Does the distance moved
change relative to the proximity to mass, and the time unit vary in value as
well? If not, do we just assume that the lack of proximity to mass in between
galaxies doesn't change the behavior of light when we say that the proximity
to black holes does?

~~~
M_Grey
It's constant _within a given frame of reference_.

~~~
abakker
So, really it isn't a universal constant, then? I guess the makes sense.

Sub question - if photons are light particles, moving at the speed of light,
then do they actually experience time dilation themselves? i.e. from the frame
of reference of the photon, is the local time for the photon ticking away in
one frame, while the outside world appears to move much much faster? Or,
relative to us is time on the photon moving very slowly?

~~~
andrepd
It _is_ a universal constant. See above.

The photon travels at the speed of light _c_. If you look at the expression
for the time dilation, you will see that it tends to infinity as _v_
approaches _c_. Remember that this relates the time experienced between two
frames moving relative to each other at a constant velocity _v_. However the
fact is that the expression fails when _v=c_ , since you have a division by
zero. This reflects the fact that it is impossible to do a Lorentz boost that
relates two frames moving relative to each other at _c_. This in turn means
concept of time dilation in an object moving at the speed of light, such as a
photon, is meaningless. There is no such thing as the time experienced from
the point of view of the photon.

I realise I probably wasn't very clear, but it's difficult to lay it all out
in a small paragraph.

~~~
abakker
That is actually a great explanation, thanks. So, photons don't experience
time? Does that mean that they don't experience entropy, either? I.e. They
don't lose any energy in transit, since to them "transit" is instantaneous.

Another question this raises for me is that if photons move in a timeless
state between 2 points, what accounts for the period of their oscillation in
the particle/wave duality? If they are tracing the fastest path through
spacetime, yet to them, the time dimension is non existent, how do they have
wave characteristics?

~~~
agentgt
I'm on mobile and not a physicist but the key is the observer. Photons don't
observe anything.

We observe them since we observe time and they do have energy changes _that we
observe_ (I believe this is how colors and red shift work).

------
brianberns
> "The whole state of system-plus-clock doesn’t change in time"

How is this different from the classical view of the universe as
deterministic? In a Newtonian universe, all future states can be determined
from the current state, so the universe can be seen as a "frozen"
4-dimensional object.

~~~
chrischen
The frozen 4 dimensional object creates a projection of the other dimensions,
including time and relative time. Time is hen a subsystem within the system.

Their analogy, aptly for HN, is that of computer code which is in one
dimension interpreted amd executed linearly, being able to project something
like a 3D game. Think something like minecraft's source code being interpreted
and creating an infinite procedurally generated world that constantly evolves
with an in game timer despite the source code still being static. Quantum
mechanics, the mechanics governing the source code could still make it
timeless and indeterministic, but output of the code (the projection), is
still bound by the in game physics and timer much like time in general
relativity.

~~~
SomeStupidPoint
But is their proposal that, like Minecraft, we can detect properties of the
background execution through apparent non-determinism (or other mechanism)?

Cause Minecraft actually has two detectable, distinct notions of time: a game
tick _and_ update ordering of the underlying computation.

Minecraft can even be viewed as having quantum effects caused by a universal
nonlocal variable, Bohmian mechanics styles, with the apparent non-determinism
resulting from that non-local hidden variable interacting woth the update
engine. (The hidden variable is the ordering of the updates in real time
rather than MC time.)

I always thought we should teach physics with Minecraft, but the engine sucks
too much for me to seriously recommend it.

Ed:

Imgur album on detecting MC update ordering via redstone; pictures somehow got
out of order.

[http://imgur.com/a/e9YKi](http://imgur.com/a/e9YKi)

------
coldcode
Reading this made me think of the question of whether our universe is actually
a simulation.

~~~
danbruc
The universe as a simulation is one of those ideas that sound interesting at
first but are actually pretty useless the longer you think about them. There
is for example also solipsism, the idea that only you exist and the rest of
the world is just in your mind, or Last Thursdayism, the idea that the world
came into existence last Thursday with all our minds filled with fake memories
of the time before last Thursday.

Those ideas put you - if you believe in them - in a spot where you can learn
nothing about the world. There is nothing that allows you, even in principle,
to figure out if there was a universe before last Thursday or if there is a
world outside of your mind. There is not much more that would allow you to
figure out whether the universe is a simulation or not.

Many people talking about that idea suggest to look for indicators of limited
computing resources, rounding error or whatnot. But that is totally misguided
in my opinion because it presupposes that you know what at least one of the
two options, the universe or a simulation of it, looks like.

Who is to say that the laws of physics of the universe do not look like they
are using floating numbers? Who is to say that a simulation of a universe may
have to deal with limited resources? The outside world could be so foreign to
us, time, space and laws of physics may not even be a thing there.
Realistically the only way to distinguish between a real universe and
simulation would be if the owner of the simulation told you in a pretty
obvious way like with small serial numbers printed on all the electrons.

I kind of understand that people don't like the idea of not even seriously
considering a substantial class of ideas that are not in conflict with what we
see and that could therefore actually be correct. It also seems not very
satisfying to throw some probabilities at them, last Thursday, unlikely, a
simulation, totally reasonable thing to do, pretty likely. In the end, if it
is not falsifiable, just ignore it and have one fewer things to worry about.

~~~
RobertoG
I don't think universe as a simulation is epistemologically equivalent to
solipsism or this "Last Thursdayism" thing (love the name, by the way).

Solipsism is meaningless. What it means to say that there is nothing outside
of your mind? Surely you can't predict or control what is going to happen to
your experience, so how can you say that everything is "inside" your mind?
what that even means? And if you are a solipsist and wanted to predict what is
going to happen next, what you should be doing?

You should start to associate causation to patterns in your experience, and
observe carefully that patterns. Those patterns behaviour are not decided by
you, so, by definition, they are outside your mind.

"Last Thursdayism" have the same problem that all the religions: OK, maybe
it's true, but.. why do you choose Thursday, why not Monday? why not one
minute ago? It's totally arbitrary.

Simulation argument has serious experimental issues, but I would not discard
it yet. Maybe we can think of something.

~~~
danbruc
I would argue that solipsism and a universe simulation are actually very
close. You observe x and it might be A or B but you have no ground truth on
what A or B looks like or how to distinguish them.

In case of solipsism you experience a universe around you but there seems to
be nothing you could use to decide whether you are experiencing an independent
outside universe through your senses or whether your mind is just
hallucinating this whole outside universe.

In case of the universe simulation you experience a universe around you but
you have no a priori knowledge what a real universe and what a simulation of a
universe is supposed to look like, you seem to be stuck in more or less the
same place as with solipsism.

 _You should start to associate causation to patterns in your experience, and
observe carefully that patterns. Those patterns behaviour are not decided by
you, so, by definition, they are outside your mind._

I think mind is probably not the right word here because it has the
connotation of control, brain might be the better choice because there are
things going on you can not control (ignoring whether you actually have any
control to begin with). It may have not been clear from my first comment, but
I was especially referring to metaphysical solipsism, denying the existence of
an independent outer reality.

 _Simulation argument has serious experimental issues, but I would not discard
it yet. Maybe we can think of something._

Personally I just don't think about it for the moment. There is surely the
possibility that we make progress one way or another, but every time I try
thinking about it, it leads nowhere. Maybe one day we discover the fundamental
laws of physics, logical self-consistent and the only self-consistent laws of
physics possible. With mathematical proof. Do we now know that our universe is
real, it is after all nothing less than the only way it could ever have been?

Or did the simulator just mess with us again? We could be using inconsistent
logic all day long, writing wrong mathematical proofs and be teaching them to
the next generation in our universities. But just before someone realizes the
error, just after we observed the contradicting consequences of our wrong
reasoning, the simulator erases the relevant memory and life goes on as if
nothing happened.

Unless somebody wants you to find out, you will never find out. The potential
enemy in this scenario is just so powerful, you can not win.

~~~
RobertoG
"I would argue that solipsism and a universe simulation are actually very
close."

I agree with you that from the point of view of testability both are very
similar, but, in my view, from the point of view of logic reasoning are almost
the opposite.

Solipsism is just bad reasoning or, at most, a semantic trick: I define my
mind as everything there is out there, so, obviously, everything is in my
mind. But we have science, precisely, to try to understand what it is out
there, and "out there" means outside of our minds.

On the other hand, you arrive to the simulation argument by deduction. That's
what, testability apart, make it interesting. The reasoning is: if a
simulation is possible, then, many are possible. If there are many simulations
in the universe, what is more probable? to be in the universe or in a
simulation?

I agree that we don't know what to do with that, but you have to recognize
that it's a damn good trick of logic.

~~~
danbruc
_I define my mind as everything there is out there, so, obviously, everything
is in my mind. But we have science, precisely, to try to understand what it is
out there, and "out there" means outside of our minds._

But that is the very point of solipsism - because you are experiencing the
outside world only through your senses in your mind, you are unable to decide
whether the outside world even exists. The two options are 1) your body with
your brain and your mind exists in the usual universe and you can learn about
the universe through your senses and 2) the usual universe does not exist,
only your brain or your body or something along that line actually exists and
the entire universe you think exists outside of your body is just something
your mind made up, your mind is simulating the universe for you.

So this is not about redefining mind to mean all the universe, it is about
emptying the universe until only your body or your brain or whatever remains,
dreaming or hallucinating or simulating the thing we just got rid of all day
long so that you can not tell the difference.

~~~
RobertoG
Well, obviously, we only have access to our senses.

As I have not control through introspection to my sensorial experience,
surely, there is something "out there" generating it. That something is what
we (or, as we are talking about solipsism, I) are trying to understand.

What is the point of saying that, what is doing it, i's "my mind"? What have
we learned doing that except to mud the issue at hand?

~~~
danbruc
I am actually a bit confused, maybe it is just because English is not my first
language and I am misunderstanding some nuances of what you are trying to say.
So let my try it from another point of view.

I personally don't dream much or at least usually do not remember much or any
of it, but in principle walking along a beach and dreaming about walking along
a beach should feel pretty much the same until you realize you only dreamed
the latter. So more or less identical experiences to you can have two very
different origins, one is rooted in some external reality, the other one is
just some kind of hallucination.

You can easily inspect the world of the real beach and at least in principle,
maybe by lucid dreaming or something like that, you could also inspect the
world of the dreamed up beach. If you never realized you were dreaming, both
scenarios might be indistinguishable for you and form the reality you are
living in, but nonetheless with very different underlying realities. Does that
make sense? There is the reality you are experiencing (beach) and there is the
reality that is causing your experience, which may (dreamed up beach) or may
not (real beach) be the same thing.

------
jcoffland
It is man's fate to forever believe that the universe is a complex composite
of his latest discovered technology.

------
grabcocque
That sounds like one of those fake papers generated by a Markov chain that
sometimes gets accepted into reputable physics journals when a researcher
wants to prove that modern physics has gone a bit... silly.

------
cm127
I just ran into an interesting theory for Gravity: Subquantum Kinetics

It's featured in Dr. Paul LaViolette's book The Secrets of Anti-gravity
Propulsion, and there's a really interesting section that challenges the
Standard Model in Quantum Mechanics called the Model G in Subquantum Kinetics.

The idea is that matter is born out of what's called the Ether, the origin to
all energy. The positive and negative electrical energy sums a positive or
negative charge with a "spin" \-- which also yields positive or negative
gravity.

This is a video that simulates matter being created out of the Ether:

[https://www.youtube.com/watch?v=jPLNfgxD2ic](https://www.youtube.com/watch?v=jPLNfgxD2ic)

Supposedly, it's been rejected by other researchers because it goes against
Einstein's theory of Relativity and the Big Bang, -- however, there's been
rumors the Model G is being used by underground, black-project sites like
Lockheed-Martin and Boeing (e.g. Northrop Grumman's B-2 Spirit stealth
bomber.)

Here's a lecture by Dr. Paul LaViolette featuring content from his book:

[https://www.youtube.com/watch?v=ifEgGMFK-
VU](https://www.youtube.com/watch?v=ifEgGMFK-VU) \- (warning: audio isn't
great)

~~~
danbruc
That is crackpottery, pseudoscience and conspiracy theory at 11. Forget about
it if you are interested in any serious conversation about physics.

~~~
cm127
I think you're proving Dr. Paul LaViolette's point why the theory is not
getting attention: emotional, knee-jerk reactions like this.

Seems like I have to agree with everything you say in order to have a
conversation about physics with you.

~~~
danbruc
It has absolutely nothing to do with what I am saying, what that guy says is
inconsistent with reality and probably with itself. Science is decided by
experimental facts, not by opinions. But he just ignores all the things we
have learned by using scientific methods in the past centuries and now know to
be true.

When you search for »subquantum kinetics«, the first result on Google for me
is »Subquantum Kinetics (a nontechnical summary)« [1] and this is from the
first two paragraphs.

 _One of its distinctive features is that it begins at the subquantum level
for its point of departure. By comparison, conventional physics and most
alternative physics theories begin with mathematically quantified observations
of physical phenomena at the quantum and macrophysical level and attempt to
deduce physical theories based on those observations. Since the conventional
approach must take into account numerous experimental observations, the end
result is a fragmented and often contradictory set of theories which must
later be sewn together with mathematical acrobatics. [...] Instead of
beginning with physical observations, subquantum kinetics begins by
postulating a set of well-ordered reaction processes that are proposed to take
place at the subquantum level._

Let me translate that. Mainstream physics does experiments and tries to
explain the results with theories using math. But the resulting math is not
beautiful so I postulate some nicer math ignoring physical reality altogether.
Admittedly he later mentions tuning his math until it matches reality but that
doesn't provide any justification for his initial choices. Nothing what he
proposes makes much sense, just have a look at this comparison chart [2]
linked to from the summary.

I am not even a physicist, but I understand enough about it that I could
probably rip apart most of the arguments he is trying to make, at least if
they make enough sense to be actually attackable. And I would do it if I were
confident that it would somehow help someone, but if you are in some way
interested in physics and look at theories like subquantum kinetics without
becoming skeptical, then chances are unfortunately pretty slim that tearing
apart such a theory using accepted knowledge will change your mind.

[1] [http://starburstfound.org/subquantum-kinetics-a-
nontechnical...](http://starburstfound.org/subquantum-kinetics-a-nontechnical-
summary/)

[2]
[http://www.starburstfound.org/SQK/SQK-c.html](http://www.starburstfound.org/SQK/SQK-c.html)

~~~
cm127
You're not really proving or disproving anything. You're just complaining he's
using another mathematical model. So what?

The worst part is you have no basis for any of your arguments, yet somehow you
feel authorized to completely dismiss the theory altogether because it somehow
offends your perspective of the world.

Either post real scientific data / material, or look up cognitive dissonance.

~~~
danbruc
I am not going to go through all the nonsense that this guy has made up over
years or decades, that is not worth the time. But if you can point to one
specific idea, prediction, refutal of mainstream physics or whatever you like
within his work, written in a way that can be understood by an interested
layman, not longer than say 25 pages or so, then I will try to explain you why
he is wrong in that instance.

~~~
cm127
Think of it this way: the Universe is continuously expanding, -- so in a way,
it's like we're still experiencing the Big Bang.

So... does that mean matter is still being produced? Yes, from the Ether.

Completely agree that it does sound crazy, but I think it makes more sense
than our current way of modeling the Universe. The interesting part is that it
invites the possibility of spiritual connections which feels amazing to
finally scientifically acknowledge.

I could be wrong, but I invite you to consider the possibility that there is
more to life than we realize. I sincerely wish you the best either decision
you make.

~~~
danbruc
_So... does that mean matter is still being produced? Yes, from the Ether._

Where do you take this from? To the best of our knowledge the universe does
not produce new matter. Space expands but that is new empty space, not space
filled with some kind of matter.

~~~
cm127
It's from the Model G theory in Subquantum Kinetics, -- and it seems more
believable than a finite amount of matter being made from a single blast of
energy billions of years ago.

~~~
danbruc
But physics is not about believing, it's about describing reality. And when we
look at our universe, we are not seeing new matter being created. If the
theory actually says that new matter is created while the the universe expands
and the amount is not so small that it may have escaped detection, then the
theory is wrong. And not because somebody believes or says something but
because the theory does not match reality.

~~~
cm127
It theoretically happens very slowly, so it probably does escape detection.

~~~
danbruc
The universe is old, at least according to mainstream physics, even small
changes would accumulate over billions of years and cubic lightyears. And we
are good at measuring things, we famously measured the g-factor to a part in a
trillion, detecting gravitational waves required detecting length changes on
the order 1/1000th the diameter of a proton, 0.000000000000000001 meters. A
quick search reveals that we know the energy density of the universe to better
than half a percent. So what are the numbers? How much new matter is generated
per unit time and volume according to the theory?

~~~
cm127
I'm still researching this, but it's happening at a quantum level, so I expect
it to be slow. But like you said, it will have an aggregate affect over time.

Also, it sounds like you're interested. Why not read the book or watch the
video lecture?

~~~
danbruc
I am not interested, I am absolutely sure that the theory is total nonsense. I
just wanted to make you realize that, preferably by making you discover it
yourself by hinting at problems, not by simply telling you that it is wrong.

