Ok but, armchair amateur here, the scale of space is not known to humans, right? We cannot comprehend the actual limit of the universe, can we? How can we know that the universe entering a dark age is not a local effect in our known universe, and that other, incomprehensibly distant parts of the universe will keep doing just fine?
For that matter, if the universe enters a dark age, what is it that caused the universe to be in a "light age" in the first place? There has be a force that causes the universe to exit a "dark age" otherwise it would always have been dark.
These kinds of things perplex me.
The cosmological event horizon is caused by the accelerating expansion of the universe. Space is expanding uniformly, so the more space there is between us and some object, the faster it is moving away from us. Objects that are farther than the Hubble Distance from us are receding faster than the speed of light, and so their light will never reach us. Over time, everything that isn't gravitationally bound to us will recede into the distance, redshift and disappear, leaving only our galaxy within the observable universe.
We don't know the scale, that's why we usually say "observable universe", but we do know the rules which apply everywhere.
"light age" or whatever you call it in this context means that there are still stars left which emit light.
After the "dark age" there will be the heat death of the universe.
It is fine to attempt to apply our rubrics, but I am not sure how to quantify the limits of our perception. Perhaps Occam's Razor and current simpler theories give a useful working tool for us to reason within our local known (or perceived/comprehended) universe.
The best way I can think of to ask this is, how do we factor in the "unknown unknown"? It is maddening not to be able to.
If you have other reasons to believe a more complex hypothesis may be likely those should generally override Occam's Razor.
> "[1:2] And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters. [1:3] And God said, Let there be light: and there was light.
If you'd like to read more, here you go: https://www.blueletterbible.org/kjv/gen/1/1/s_1001
I will note that in the above it says "morning" and "evening". In some sense, the writing is old enough that we assume that is what the original hebrew meant, but we don't actually have context to say. I've heard that the word for "morning" (erev) could have meant "order", and "evening" (boker) could have meant "disorder".
So what you get is 7 days (depending on who you ask) where the second law of thermodynamics is "wound up", if you will, which resulted in an ordered universe that isn't just a homogeneous soup.
Please... please don't imply that the book of Genesis, or any similar religious work, holds some hidden insight into modern science. The authors of Genesis, whoever they were, did not know what thermodynamics was, and were not writing about it when they came up with the Genesis account.
I didn't. Nor was that my intent. I only wanted to point out that there was something interesting and relevant to the above post.
I encourage you to take some time and study the Christian church during the Middle Ages. Much of what we consider 'modern' learning, teaching, and method came about because there were monks an nuns who were very serious about their work.
Likewise, I encourage you to study Islam since its inception; there also clerics (I don't know the proper terms) sought to increase understanding in literature an science some 500 years before the church in Europe.
Also take some time to look into various religious orders (Hindu, Buddhism, and others) throughout Asia that, in very similar fashion, worked to preserve and expand knowledge within their orders and in their surrounding communities.
If anything, religion has been a driving force towards foundational methods of understanding, knowledge acquisition, and preservation.
My intent was to add an extra dimension to the conversation.
In the big rip scenario, dark energy will overpower all other forces and at some point space itself will expand so fast that the cosmic event horizon will be smaller than the smallest particle which means that nothing will be able to reach anything (even particles).
In the big crunch scenario expansion will stop at some point and it will reverse and in the end the whole universe will be concentrated in a point (just like before the big bang).
Equilibrium means that the expansion stops but does not reverse.
What do you mean by "surface tension"?
I was making an analogy to the behavior of fluids in our reality. Really though, what I was getting at is, do we, or can we, really know the nature of the universe to such a degree that we can rule out behaviors which may change as the universe progresses through whatever sequence of events through which it is progressing? I think you answered my question, such as it was.
> In the redshift range 100<(1+z)<137, ...
z is the letter often used for redshift, https://en.wikipedia.org/wiki/Redshift, a stand-in for cosmological time that's easy to extract experimentally (as compared to an actual time). (1+z) is essentially the ratio by which the universe is bigger today than it was when the physics being observed happened.
If a previous civilization had metal-based moon landers, would we likely have found them/found areas with an unlikely amount of metal on the moon? Or would they have probably been obliterated by meteorites by now?
We can't exclude the possibility that previous civilization also decided or was forced to abandon all its technology due to reasons known to them - that is, if they were enough advanced to have space-reaching technology.
For the moon thing, the above applies, but assuming that they were obliterated we’d have to get pretty lucky to detect their remains. They could also be totally intact because there would be essentially no weathering, they would never be buried by shifting regolith, and so on.
I would think not much?
Over millions of years that will add up, honestly I'm hoping someone else will do the math/research and figure out if they add up to enough that they wouldn't still be orbiting earth.
"The Silurian hypothesis: would it be possible to detect an industrial civilization in the geological record?"
Any evidence of civilization from that period would either be hella deep under the sea or obliterated by glacial expansion and retreat.
Homo sapiens have been here 300k years. I find it ridiculous to assume we only started living in cities about 5-7000 years ago. Conveniently the period immediately after the last rapid glacial retreat...
So according to your hypothesis, civilizations would have emerged from hominids other than the homo sapiens, contrary to what we know about them. And their cities would all be in the North of Europe, where the later glaciation could hide some archaeological proofs. And we could not detect anything, though an Ice age doesn't destroy anything.
I believe there is no fact to sustain that hypothesis, and many facts against it.
Well new evidence suggests that humans colonised Aus around 65k years ago. There is also some evidence of human activity in the Americas thats far older, although the evidence is scant at the moment.
> There was no glaciation or sea change to destroy the evidences.
No sea level change? With the last glacial maximum the sea level was about 120m lower than now, wasn't it? Is it not reasonable to assume coast settlements or cities would now be submerged? There was continental-sized areas of land lost during that sea level rise. The amount of land lost in Asia alone is staggering.
> I believe there is no fact to sustain that hypothesis, and many facts against it.
Perhaps, but new evidence keeps on being discovered and lets not forget that lots of facts may simply be submerged under hundreds of meters of seawater.
Its fun to keep an open mind.
At least these archaeologists beg to differ:
Even in Egypt stuff are still being (last pyramid discovered in 2008, a tomb buried under the sand last december).
The Sahara is approximately the size of the US and India combined, and we know it was still green during the Early Dynastic Period of Egypt. Lot of place for humans to settle, now all covered in sand.
- complexity and type of tools & technology dug up
- change in pollen due to agriculture
- change in genetics of domesticated animals
None of these (as far as I know) point to cities or civilisations that didn't have cities (if such a thing is conceivable, which it could be) way further back than the current records show.
Or, we're indeed in a simulation which is aimed to preserve the image of species that evolved beyond physical form eons ago.
If we look like the Sims to them, the current player may find it funny that we refer to their Game Devs as being part of a past civilization, which could make them wonder if they're part of a sim...
Edit: if you are ever interested in reading it, the Wikipedia plot part reveals the whole story, end included
It makes me wonder if the Ancient Aliens guy might be partially right.
At that time scale, exploring the entire galaxy seems reasonably practical. And stopping here to refuel and recuperate, not so unlikely, at least to me.
A lot of SF is really bad in they assume people will be the same and just drive to different galaxies instead of drive to different states. But the technology between the two is so huge that to get there would probably entail a whole host of things that would transform them into something above us as mayflies are to us. Not sure we'd even be able to tell if they left anything or even stopped by.
Consider human civilisation circa 3000 years ago. People moved around on horses, with carts. Roads were usually poor or non-existent. We are incomparably advanced compared to back then. But:
• They had outposts for travellers and we have airports.
• They had to feed their horses, we have to refuel planes.
• They needed infrastructure to establish new towns and colonies. We do too although the Earth being inconveniently full of cities often hides this fact.
Whilst the technology has changed enormously the fundamentals of travel and colonisation haven't. If there's no refuelling process at all ever then that implies a violation of the conservation of energy laws anyway - even if you only refuel once when a ship is newly built with some incredibly long lasting energy source, that's still fueling.
As far as is known, the only way to generate gravity is mass, and the only way to counteract gravity is to push against it in the other direction hard enough, but that's just rocketry.
Imagine for a moment that we're Martians who managed to terraform Earth because of some runaway climate catastrophe on Mars. That now, we're in the early stages of repeating the same mistakes because of some extinction event in the past that wiped out all of our prior history and knowledge.
So why do humans find it easier to conceive of terraforming Mars, than to just fix our planet instead?
It would have had to have been going on long before intelligence arose though, which is not impossible.
I don't think this is consistent with DNA evidence, since such cross pollination would be expected to show up as two sets of genetic lines of descent with very different characteristics, since the environment of Mars is very different from that of Earth; and we don't observer anything like that. In fact, if life was evolving separately on Earth and Mars, it might not take very long before the two lines of descent were not even compatible genetically, meaning that genetic exchange would be impossible even if the organisms were brought back together.
believers in most traditional religions declare piously that the climate changes of the last ten millennia are the results of human misbehavior, while rationalists insist that this is all superstition and the climate changes have perfectly natural causes.
If you were a waterworld hyper-squid making this comment, you might be arguing that no life form with neurons measuring only microns in diameter could possibly respond fast enough to environmental stimuli to behave intelligently. We, with our myelinated neurons, know better; squid neurons aren't myelinated and do in fact need to be humongous to transmit signals quickly, but our myelinated neurons don't.
If there was some kind of apparatus capable of signal-processing, control, homeostatic feedback, language and visual processing, and at times seemingly intelligent behavior, while using switching and storage elements only tens of nanometers in diameter, which operate a million times faster than the switching and storage elements in your head (assuming you're a human), you might see the flaw in your inference. That's about twelve orders of magnitude denser processing power per unit volume: six orders of magnitude higher speed and six orders of magnitude lower volume. Of course, a hypothetical alien signal processing device that small (call it an "omvindnojm") might only be capable of very simple operations compared to a neuron, but maybe several of them together could be a feasible substitute?
Naw, who am I kidding? Such a thing is probably impossible. Your mammalian neurons are as good as it gets, kid.
Edit-this is also why I’ve never considered the threat of a singularity creating a malevolent super-AI to be serious. Larger brains do exist on earth and they only kill humans rarely.
As per the wikipedia's page on brain-to-body mass ratio.
And another series, I wish I could read again but cannot remember the author or titles, but it was about a world where civilization ended because we'd genetically engineered ourselves and animals and everything into fairy tale creatures who overran everything. The whole time it seems like it's set in the future but it ends up the main characters become Adam and Eve and it implies all our current mythology came from the society that genetically engineered themselves out of existence.
Won't the plastic eventually turn back into oil, on geologic timescales? Or are the conditions for that too specific to be relied on? Or am I completely mistaken, and oil->plastic is basically one-way?
This is addressed in the article:
“...our work also opened up the speculative possibility that some planets might have fossil-fuel-driven cycles of civilization building and collapse. If a civilization uses fossil fuels, the climate change they trigger can lead to a large decrease in ocean oxygen levels. These low oxygen levels (called ocean anoxia) help trigger the conditions needed for making fossil fuels like oil and coal in the first place.”
Also "The Hab Theory" by Allan Eckert.
Star Trek Voyager had an episode with the idea of an ancient saurian species that left earth many millions of years ago. https://en.wikipedia.org/wiki/Distant_Origin