Fate of Universe revealed by galactic lens

[Dretlin]

Interesting article on the BBC site.

[karadan]

It is kind of eerie to think that in a few trillion years, there will be nothing other than black holes and red dwarfs floating about the cosmos.

[Dretlin]

It is kind of eerie to think that in a few trillion years, there will be nothing other than black holes and red dwarfs floating about the cosmos.

I was aware that this outcome was possible. "Eerie" is perhaps the most appropriate word to use.

Probably best we leave the universe.  

[Tank]

It is kind of eerie to think that in a few trillion years, there will be nothing other than black holes and red dwarfs floating about the cosmos.

I was aware that this outcome was possible. "Eerie" is perhaps the most appropriate word to use.

Probably best we leave the universe.  :hmm:  Where would we go?

Interesting link.

However, Dark Energy and Dark Matter are still just 'place holder' names for as yet undefined forces or apparent space time distortions. There is still the issue of Quantum Gravity to be solved and until that and the 'Standard Model' are unified the one thing we do know for sure is that we don't know everything.

[karadan]

It is kind of eerie to think that in a few trillion years, there will be nothing other than black holes and red dwarfs floating about the cosmos.

I was aware that this outcome was possible. "Eerie" is perhaps the most appropriate word to use.

Probably best we leave the universe.  :hmm:  Where would we go?

Other, younger universes of course! Duh  

[Dretlin]

:hmm:

I wonder if this model will hold up in the future.

[Tank]

:hmm:

I wonder if this model will hold up in the future.

Exactly my point. They may well be right in their observations but as some of the apparent causes of those observations are currently not 100% watertight then there may be 'wriggle room' later when somebody does have a 'Eureka' moment and figures out the real relationship between Quantum Gravity and the Standard Model.

[humblesmurph]

are there any competing interpretations of this data?

[Dretlin]

are there any competing interpretations of this data?

I am unsure, though I will look and would encourage anyone to share it if they find it.

[hackenslash]

They are placeholders for 'we don't know yet' in precisely the same way as gravity is. They are descriptions of effects. What the cause is of those effects is not yet known, in all three cases, but the effects are real and observable. There's no mystery here. In the case of, for example, dark energy, we know that the expansion of the cosmos is undergoing acceleration, which is an effect that needs to be accounted for, so they came up with energy that can account for it, but of course we haven't actually observed this energy, only it's effect. Again, the same is true of gravity. We don't know what causes gravity, but we know it exists.

[skwurll]

It will eventually become a cold, dead wasteland, researchers say.

Like Russia?

[Asmodean]

It's all going down the drain... Welcome to MY world  

Our universe does have to end one day - if not for one reason, than the other. However, I think it might just be that in the cosmic dust of our universe, a new universe will be born. Without humans in it, but not being a fan of our species, I don't see it as a bad thing.

[Tank]

They are placeholders for 'we don't know yet' in precisely the same way as gravity is. They are descriptions of effects. What the cause is of those effects is not yet known, in all three cases, but the effects are real and observable. There's no mystery here. In the case of, for example, dark energy, we know that the expansion of the cosmos is undergoing acceleration, which is an effect that needs to be accounted for, so they came up with energy that can account for it, but of course we haven't actually observed this energy, only it's effect. Again, the same is true of gravity. We don't know what causes gravity, but we know it exists.

Good point. Although would I be right in saying we have a better understanding of the effects of gravity than that or DM & DE?

[Tank]

are there any competing interpretations of this data?

I have not seen any and as it is a recent study and release of data it will be a while before we do see any reasoned criticism as opposed speculative comment.

[hackenslash]

Good point. Although would I be right in saying we have a better understanding of the effects of gravity than that or DM & DE?

Not precisely. It's a bit of a thorny problem, TBH. The fact is that DM and DE may well represent how poorly we understand gravity.

Dark matter is postulated because, given our understanding of gravity, there isn't enough detectable mass in the universe to keep it all hanging together without flying apart. This actually includes gravitationally bound entities such as galaxies, which simply must contain more mass then can be observed to remain gravitationally bound.

Dark energy is postulated because recent observations demonstrate that cosmic expansion is actually accelerating, which means it's overcoming the gravitational attraction present in the cosmos. That's why it's being touted as a 'cosmological constant', the idea being that the influence of dark energy was there from the beginning, but that until expansion reached a certain phase, its effect was damped by gravitational attraction. As the expansion passed this phase, DE could reassert its influence and cause expansion to accelerate. It seems like an additional entity, which is why the credulous jump on it as something that we have faith in while not being able to see it, but it's quite parsimonious at bottom, because something is causing expansion to accelerate.

In short, DM and DE represent a better understanding of gravity than we had previously, and are actually functional in gravitational terms. The only thing is, we don't actually know why. In reality, DM and DE, when treated as separate from gravity (which is always going to be problematic, precisely because they are a description of effects related to gravity in one way or another), are precisely as well understood as gravity. We can measure and describe their effects quite precisely, but we don't actually have the faintest idea of what they actually are. We can say how gravitationally bound objects should behave with the mass they are observed to contain, and we can measure how much our observations diverge from those predictions. This represents a measurable understanding of dark matter. We can also say that we understand how cosmic expansion should proceed under our understanding of gravity, and we can measure the divergence from those predictions. This represents a measurable understanding

One caveat is this: If Einstein was correct, then we at least have some picture of gravity as the warping of spacetime, but we have no clue about what causes that warping, so we're pretty much where we were before. It also isn't absolutely clear that Einstein was correct in this regard, and we won't know much more until some serious experiments are carried out, some of which are scheduled for the LHC when it gets to doing physics at full chat. If the Higgs-Boson is discovered, then we have the Higgs field, which will give us a mechanism for the warping of spacetime, and it is actually the warping itself that imparts mass in this model. Then, of course, we have the graviton, which would actually make gravity a force, because this is a force-carrying particle, akin to the photon.

It may also be that M-Theory is on the right track. This gets a little more complicated.

A good book that deals with a lot of this in quite accessible terms is Brian Greene's fabulous Fabric of the Cosmo. He also deals with some of the ideas arising from M-Theory (this is actually his own field, so it gets a fair bit of the airtime in his book). One thing I will say about the book is that it's important not to get too hung up on his treatment of entropy which, being laid out in terms for the layman, is less than rigorous. He, like many popular science authors, treats entropy as disorder, and doesn't really deal with it in a manner that makes it clear precisely why entropy is most readily described as disorder, while not actually being disorder. I found myself screaming at the pages on occasion, because his treatment is actually quite misleading.

Anyhoo, I hope that clears some of it up. I had intended this post to be quite terse, but got carried away somewhat.