Maybe there is no Hubble tension after all.
New research with the JWST found values that are within the margin of error.
Nah, it’s still there.
Way back when before we were sure of an ongoing expansion, the idea of expansion then gravity pulling everything back into a ‘Big Crunch’ seemed attractive to me. And then of course a new big bang. Ongoing cycles was satisfying to me and I was a tad sad when I accepted the unending expansion and eventual heat death of the universe. And the end of everything I suppose.
I’m sure that’s the reason I had a dream about it. In my dream, the ‘shape’ of the universe was round. The Big Bang started the expansion down the sides of the ‘ball’. Once the expansion reached the equator, it speeds back up into a Big Crunch on the other side.
Me too. Continued expansion without end is just about the most lonely, and depressing eventual fate of the universe I can imagine.
I looked for an online demo, but couldn’t find one. So I made my own:
Hubble Expansion
You can drag the overlay around to see the center change.
Maybe they should call it Schrödinger’s tension.
I very much doubt that heat death will be the final word on what the end state of the universe will be. I mean, look at all the things that would impact that prediction:
- We don’t know what dark matter is yet
- We don’t know what dark energy is yet
- We don’t know what caused inflation, why it stopped, or even whether it stopped
- We don’t know if it makes sense to talk about a maximal entropy state for the entire universe
I hate to sound like “what the bleep do we know”…I think it’s perfectly reasonable for astrophysicists and cosmologists to say “based on what we know right now, the universe is heading to heat death”.
I just think there should be a clearer demarcation between extrapolation like this and more foundational science, because the general public can confuse the two.
I abmit that I’m a member of the ‘general public’ but shouldn’t that read:
- We don’t know IF dark matter is yet?
“ In astronomy, dark matter is a hypothetical form of matter that appears not to interact with light or the electromagnetic field.” - We don’t know IF dark energy is yet
” In physical cosmology and astronomy, dark energy is an unknown form of energy”
But for my general feeling of malaise about it, the heat death will do it. I doubt very much anything we would consider “life” could live on past heat death.
And I read on these boards that in the very far future that the universe will have expanded to the point that being able to look out and see other galaxies will be over. That also gives me a feeling of loneliness.
But these are just musings. It’s nothing I lose sleep over and it’s certainly not scientific. Just sharing a feeling.
Dark matter is supposed to be real matter, but it is not some kind of space dust, you cannot see it (therefore its existence has to be confirmed in other ways), hence the name.
I think if you want to get really technical, the most accurate way to put it is, “we don’t know if Dark Matter is really matter, or if Dark Energy is really energy”.
We see the universe behave a certain way. Stars and galaxies are clustered in ways that don’t make sense based on the matter we can see, but would make sense if there was additional matter there that interacted with the other matter gravitationally but not in any other way. Hence, “Dark” Matter.
That observation - that the universe behaves as if there was a bunch of extra manner - is a real observation. So “Dark Matter”, the phenomenon that we observed, is real. Whether it is caused by actual matter that’s dark, or by gravity having different rules at very large scales, or something else - we don’t know yet.
Same goes for Dark Energy. The expansion of the universe is spreeding up, and the further apart two spots are the faster they grow apart. We describe this as “Dark Energy” and it’s clearly a real phenomenon, but whether it is literally caused by energy entering the universe or being created somehow, or by something else - again, we don’t know.
We don’t see Dark Matter but theoretically it could be normal matter. It’s just that if it was dust, it would need to be such incredible amounts of dust that we definitely would expect to see it (or for it to collapse into stars).
One theory is that it is a bunch of black holes, but we would still expect to detect them through gravitational lensing. So a theory exists that suggests dark matter (the phenomenon) is caused by trillions of tiny black holes that couldn’t form under the conditions the universe has now, but theoretically could have under the conditions of the early universe - hence the term ‘primordial black hole’.
But there are flaws with that theory, which means the consensus is that the dark matter phenomenon may best be explained by a special type of matter called non baryonic matter. This type of matter would not have the standard subatomic particles and thus would follow very different rules for interacting with normal baryonic matter. Which could explain why we don’t see it (why it is dark).
If that theory is true, then dark matter would be a real thing distinct from normal matter. But if the dark matter observations are caused by black holes or dust, then dark matter is just regular matter we can’t see.
Yes, I understand that. My post wasn’t really meant to try to define dark matter - that is way above my pay grade - I was responding to Mijn’s post that dark matter, the substance, could prolong the end of what we know about the end of the cosmos. If it is a type of matter, it might or might not. If it’s a property of gravity, it probably wouldn’t. So we can’t say it will affect the end of what we know about the end until we know what it is.
Pretty much what @Babale said.
Or, to put it in my own way and taking the example of dark matter, there’s the phenomenon, and then there’s the theory.
(ETA: I didn’t realize how much I was repeating what Babale said at time of writing)
The phenomenon is that visible matter behaves as though it is receiving an additional gravitational tug. There are many lines of evidence for this now (not just the movement of stars and galaxies, but also gravitational lensing, the structure of the CMB, etc) so we can be pretty confident that dark matter the phenomenon is real.
But “dark matter” of course includes the word “matter” in the name, so it is also used interchangeably to mean the theory that the phenomenon is caused by some kind of cold non-baryonic matter. This remains the most likely possibility, but we won’t know until we make the particles and/or figure out a definitive test for them (or an alternative explanation gets strong confirmation).
But in terms of my point about heat death it doesn’t actually matter.
If dark matter is matter then that matter might have properties that influence the future course of the universe; particularly if it self-interacts in some circumstances.
And if it’s not matter then all bets are off.
And note that dark matter was just one of my list of 4 things that affect the heat death prediction, and I don’t think my list was comprehensive.
And there may be other possibilities not considered yet.
Exactly. And the burden of proof is not on me, because I have made no claim about the end of the universe.
My position is simply that the current extrapolation to an end state is built on a tower of various blocks of frontier science, so I strongly suspect it will be revised.
No, the most depressing cosmological model is the one where the Universe extends infinitely far into the past, always contracting, and is headed to an eventual Big Crunch a finite time in the future.
Meanwhile, a good case can be made that we’re not heading towards the Heat Death of the Universe, because it already happened, long, long ago. Stars, planets, even atoms, protons, and neutrons, are all just the decaying embers of a fire that went out in the first fraction of a second.
We’re quite confident that dark matter exists, and in fact it would be somewhat surprising if it didn’t. We just don’t know the precise properties of the stuff that makes it up.
Dark energy, well, we’re extremely confident that there’s some sort of phenomenon there, but you’re right that it’s not at all certain that it should be thought of as a form of energy.
Some of the dark matter certainly is “normal” baryonic matter (I put “normal” in quotes because baryonic matter, the stuff we consider normal, is only a small fraction of all matter). But it can’t be very much: If baryonic matter were more common, then deuterium and the various isotopes of helium and lithium would be more common than they are. From the observed relative abundances of isotopes, we can put fairly tight bounds on the total amount of baryonic matter, and it’s not nearly enough.
Astrophysical black holes (i.e., those formed from the collapse of stars or similar objects) count towards this baryonic total, because they would have been baryonic matter at the time of Big Bang nucleosynthesis. Primordial black holes are still a possibility, but they can’t be too large or we’d have seen them through lensing, and they can’t be too small or they’d be common enough for us to have seen some up close (though there is some window of room between those bounds).
I would be very surprised if some heretofore-unknown property of dark matter were to forestall the heat death of the Universe, or in any other way have any significant effect on cosmological models. Dark matter is only mysterious in the same way as, say, urban graffiti: Sure, we might not know who did it, but we’re pretty sure that it was some young male with a can of spray paint when nobody’s looking. We’d like to catch him in the act, but it wouldn’t really revolutionize our understanding if we did. Dark energy, though, that’s a big shrug. Maybe?
I dont understand why there is no center of the universe. I understand all about the redshift and the balloon and so on. But if it came from a singularity, it must have been “somewhere” no?
Sure. That place is here, and also there, and also everywhere in the whole universe.
If there are two spots in space and they are 1 light year apart, and you go back some amount of time towards the Big Bang, they would now be closer, right?
Keep rewinding the tape far enough and they are on top of each other, and so is the point that’s 100 light years away or 10 billion light years away in the present day.
That’s what “singularity” means in this context. It’s where all points converge and the universe exists as just one point.
Thank you for the response, but still, if i was the FSM and had a great VHS tape from the beginning to now. Wouldnt i be able to rewind the tape and see where it all originated?
Sure you could.
To be clear, you are looking for the point in today’s universe that corresponds to the point where about 13.7 billion years ago the Big Bang occurred, right?
Well, what happened at the Big Bang? The universe, which up until then was squeezed into a single point, began to expand.
So you can pick any arbitrary point. Was the Big Bang at that point? Either it was, or it overlapped with the point that was (since every point overlapped), so the answer must be yes.
That’s why CMBR - Cosmic Microwave Background Radiation - the sound of the Big Bang - echoes at us from every direction. It occurred at every point, so the noise of it comes in from every direction.
Oh thank you, that was a good explanation!