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Forum » SpaceEngine » Science and Astronomy Discussions » When will all the energy in the universe be exaused? (What happends next.)
When will all the energy in the universe be exaused?
JOEBLOGGSDate: Monday, 20.04.2015, 10:54 | Message # 1
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How much longer do we have till all the energy in the universe is exhausted and what happens next?




ONE DAY I WILL HAVE A POWERFUL GPU TO RUN THIS GAME

Edited by JOEBLOGGS - Monday, 20.04.2015, 11:01
 
VoekoevakaDate: Monday, 20.04.2015, 11:41 | Message # 2
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Accoarding to conservation of energy, it will never be exhausted. But it seems that the universe keeps growing, so the energy density is dwindling. Noone knows how this will continue, as we don't understand things like dark matter, dark energy...




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WatsisnameDate: Monday, 20.04.2015, 18:59 | Message # 3
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Voekoevaka is right. According to conservation laws, the total energy of the universe must be constant (though energy per volume goes down with expansion). But I think your question is actually asking "when will the energy available to do work be exhausted?" This is essentially a question of entropy, or the second law of thermodynamics, which says that the entropy of a closed system must either be constant, or increasing anytime there is an irreversible process.

As far as we know, the universe can be treated as a closed system, and it is full of irreversible processes. So the entropy is indeed increasing. Like a clock winding down, it will have less and less energy available in a useable form. Eventually, star formation will cease, all stars that existed will die, and the mass of the universe will be locked away either in black holes or as radiation. Even this radiation will only get more diluted as the expansion continues. The very distant future is an extremely boring place.

How long do we have until the available energy is exhausted? Long. So long that I'm not worried about it, anyway. smile

The sun's slowly increasing luminosity will render Earth uninhabitable in the next billion years or so, and the whole solar system uninhabitable in about five billion, but if humans are still around and capable of interstellar flight, then they could survive happily for trillions of years around lower mass stars. Eventually those stars too will fail, and humans will have to look for another source of energy: black holes.

A significant fraction of the mass of a rotating black hole can be harvested by the Penrose process, and for a black hole weighing billions of suns and rotating at nearly the fastest possible rate, this could support an advanced civilization for a very long time, even after all other forms of available energy have been spent. But even these very large reservoirs of energy are finite, and in an expanding universe there are only so many of them within one's cosmic horizon, and so, sooner or later, all life in the universe will necessarily end.

Quote Voekoevaka ()
But it seems that the universe keeps growing, so the energy density is dwindling. Noone knows how this will continue, as we don't understand things like dark matter, dark energy...


That's not entirely accurate. We understand very well what dark energy and dark matter do. We just don't really know what they are, (though we have some pretty good ideas).

Dark matter is by far the less mysterious of the two. It's basically just like "regular" matter, except that it does not interact by electromagnetism. So we can't see it, but we can detect it by its gravitational effects. The gravitational field of dark matter has a braking effect on the universe's expansion rate, again just like regular matter.

Dark energy has the opposite effect. It is like a very small anti-gravity over the whole universe (one may think of this as a property of the vacuum, where it has a slight negative energy density). This has an accelerating effect on the expansion rate.

So, how does the universe's expansion play out with all of these different substances participating? Let's break it down:

If the universe was only made up of (regular) matter, then it turns out that there is not enough of it to halt the expansion. Such a universe is called "open", meaning it expands forever. It is like a rocket put on an escape trajectory -- the velocity decreases, but never to zero.

With a higher density of matter, the braking effect is stronger. There is a certain "critical density", akin to the escape speed of a rocket, where the expansion rate asymptotically approaches zero after infinite time. This is called a "flat" universe. If the universe's density is greater than the critical density, then it is "closed", and the expansion rate reverses and the universe collapses again in a Big Crunch. In the rocket analogy, this is like being on a suborbital trajectory. It goes up for a while, and then right back down.

There is about five times more dark matter than regular matter, and together they provide almost exactly enough density to equal the critical density of the universe. So with dark matter and regular matter, the universe would be flat.

The existence of dark energy tips the balance back to "open". As long as dark energy's density is constant like we think it is, then its accelerating effect on the expansion will grow stronger with time. (The density of matter and radiation decreases as the universe expands, so the relative abundance of dark energy increases. Dark energy becomes more relevant over time.)

There are other models of dark energy where its density is not constant over time, in which case the future evolution of the universe might be pretty crazy. For example, if its density grows over time, then the expansion rate could increase so rapidly that all structures are torn apart in a "Big Rip". Current observations are inadequate for determining if the Big Rip will happen or not, but most cosmologists don't think it is likely. The simplest working model for dark energy is one where it is constant. (We're also very sure that its density does not decrease with time, as this is inconsistent with the observed evolution of the universe. If it does decrease, then it can only do so much more slowly than matter and dark matter.)

-edited for typos.





 
parameciumkidDate: Tuesday, 21.04.2015, 01:42 | Message # 4
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So who here's heard that news blurb about how they calculated that the universe will end in the next few dozen billion years? Apparently it had something to do with a dark energy constant of some kind.
I'd sure like someone to explain it a bit more clearly, because the video I saw about it was rather unclear xD Personally, I have serious doubts. I'm not an astrophysicist, but what I do know about the universe suggests that we probably live close to the beginning of its lifespan.





Intel HD Graphics 4000 ;P
 
WatsisnameDate: Tuesday, 21.04.2015, 04:08 | Message # 5
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That sounds like the Big Rip scenario, first proposed by Caldwell et al. in 2003. I'd say that you would do well to doubt it -- most cosmologists doubt it as well. Here's a couple of things to say about it:

1) The theory assumes that dark energy is more complicated than in our current working model (in which it is simply the cosmological constant, or Λ as it appears in the Einstein field equation). As a cosmological constant, dark energy's density is a constant over time. In the Big Rip, they instead assume that dark energy grows stronger with time (in which case it is often called "phantom energy" or "quintessence" depending on the model used.)

2) The time it takes for the Big Rip to happen could be anything from billions of years to infinity. It depends on how quickly dark energy grows stronger with time. This can be characterized by its equation of state with a number "w". If w is less than -1 (and it must be less, not equal), then a Big Rip occurs. The farther below -1 w is, the sooner the Big Rip happens.

Unfortunately, w is very difficult to measure. Last time I checked (it's been a few years, maybe we can do better now), -1 was in the middle of the estimated range, but the error bars are quite large. So the best we can say from observations is that dark energy is best modeled as the cosmological constant (where w=-1), but we cannot rule out the other types.





 
BlueDracheDate: Tuesday, 21.04.2015, 17:45 | Message # 6
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Reminds me of
https://www.youtube.com/watch?v=F1CddzgVW14
 
parameciumkidDate: Tuesday, 21.04.2015, 19:11 | Message # 7
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Here's the article I read: http://phys.org/news....le.html
It's predicting a Big Crunch, oddly enough. I had more credulity for the Big Rip scenario simply due to its simplicity (and it wasn't my first choice either).





Intel HD Graphics 4000 ;P
 
WatsisnameDate: Tuesday, 21.04.2015, 22:43 | Message # 8
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BlueDrache, OMG that video is amazing. Thank you for posting that. smile

parameciumkid, when I saw Big Crunch my first thought was "How old is this article?". Big Crunch end states were all the rage back before we knew about dark energy, when research focused on trying to figure out whether the matter density made the universe flat, open, or closed. I had no idea anyone was currently modelling dark energy in a way which revives the Big Crunch scenario. It of course can be made to work that way, but then, like the Big Rip, you're not dealing with the cosmological constant anymore, but something more complicated and conjectural.

In this case, they're talking about a mechanism by which dark energy can be "sequestered" (I'm not entirely clear what that means or how it works), and that their motivation for theorizing this mechanism was to explain the discrepancy between the observed value of dark energy versus its predicted value from quantum field theory (AKA the worst prediction in the history of physics). They claim that their theory naturally reproduces the observed history of the expansion rate (rather than having to be tuned, in which case it is ad hoc), and furthermore it shows that dark energy's gravitational effect changes from repulsive to attractive, and thus leads to a Big Crunch in the "near" future.

I'd say that I am much more skeptical of all of this than the Big Rip scenario, but honestly I really don't understand it well enough to draw conclusions. I've never heard of "sequestering" dark energy, nor do I understand the physics behind it (apparently this is something they are developing on their own). I'm sure it's not as absurd as it sounds (though it better come with potentially testable predictions), but the article doesn't explain it very well. I'll have to see about tracking down their paper(s) to try to figure out the details.





 
parameciumkidDate: Wednesday, 22.04.2015, 06:33 | Message # 9
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Ahh yes, the good old Quantum Catastrophe. I love telling physics nerds I know about that (those who don't already know of course).

I found that in the video the interviewer kept asking the scientist for explanations and the scientist kept rambling incomprehensibly or dodging questions. There wasn't a clear explanation in there as to how or why they actually came to any of these conclusions, which more than anything else contributed to my skepticism.





Intel HD Graphics 4000 ;P
 
FastFourierTransformDate: Wednesday, 22.04.2015, 08:43 | Message # 10
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One related question I always had:

If the entropy of the Universe today is 4.3 x 10^81 J/K how much entropy will have the Universe when the heat death arrives? How much entropy does the Universe will have when it arrives to it's final state of total equilibrium?
 
BlueDracheDate: Wednesday, 22.04.2015, 12:09 | Message # 11
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Quote Watsisname ()
BlueDrache, OMG that video is amazing. Thank you for posting that. smile


Oh, you're welcome. I thought it was cool that he plugged Space Engine too. spumwhack applies some interesting real-world concepts to his play of Minecraft.

Quote FastFourierTransform ()
How much entropy does the Universe will have when it arrives to it's final state of total equilibrium?


That's easy ... ∞


Edited by BlueDrache - Wednesday, 22.04.2015, 12:13
 
parameciumkidDate: Wednesday, 22.04.2015, 21:28 | Message # 12
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Or zero, oddly enough. Entropy's one of those odd concepts where an infinite amount and nothing are fundamentally the same - if you disperse every particle in the universe into a perfectly even distribution with perfect equilibrium of energy, you could easily argue that the universe has reached a state of perfect organization and thus no entropy at all.

...If I've only learned one thing about mother Nature, it's that she has no respect whatsoever for human logic xD





Intel HD Graphics 4000 ;P
 
WatsisnameDate: Wednesday, 22.04.2015, 22:10 | Message # 13
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Quote BlueDrache ()
That's easy ... ∞


How did you arrive at this answer?

Quote FastFourierTransform ()
If the entropy of the Universe today is 4.3 x 10^81 J/K how much entropy will have the Universe when the heat death arrives? How much entropy does the Universe will have when it arrives to it's final state of total equilibrium?


I think you would enjoy the paper that the wikipedia article cites for that figure, it's extremely fascinating and will help answer your question. smile In particular, check figures 6 and 7. (Also keep in mind that they use entropy with dimensionless units, by dividing it by the Boltzmann constant: k=1.38x10-23 J/K)

Currently, most of the entropy of the universe (where we're referring to our cosmic event horizon plus the contents therein), lies on the horizon itself. For the interior, most of the rest is stored in black holes (black holes are excellent reservoirs of entropy; it can be shown that a black hole is the maximal entropy state of a system.)

In the very distant future, black hole entropy will decrease as they evaporate by Hawking radiation, which will correspond to an increase in entropy of the environment (via the radiation). But the total entropy does not increase very much through this process. Since there aren't very many other processes going on (hence the thermodynamic "heat death" of an open universe), the entropy increases more and more slowly as the universe ages.

It turns out that the total entropy is already pretty close (in a log sense) to the maximum. The vast majority of the entropy gain happened very early on, when the universe was less than a second old.





 
WatsisnameDate: Wednesday, 22.04.2015, 22:21 | Message # 14
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Quote parameciumkid ()
Or zero, oddly enough. Entropy's one of those odd concepts where an infinite amount and nothing are fundamentally the same - if you disperse every particle in the universe into a perfectly even distribution with perfect equilibrium of energy, you could easily argue that the universe has reached a state of perfect organization and thus no entropy at all.


No, entropy of a real system is never zero or infinite. A "perfectly organized system", like a perfectly uniform sea of particles, has nonzero entropy.





 
BlueDracheDate: Thursday, 23.04.2015, 00:18 | Message # 15
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Quote Watsisname ()
Quote BlueDrache ()
That's easy ... ∞

How did you arrive at this answer?


Common sense guess with the assumption that entropy increases as a system becomes more disorganized.
 
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