Will the Universe End?

[Darth Raptor]

Okay, I won't even pretend to be well-versed in physics or cosmology, but something has been bugging me. It's well-established that the observable universe is open, right? By that I mean that there isn't enough mass to stop the expansion and cause it collapse back in on itself. Furthermore, something seems to be speeding up said expansion IIRC.

Now my question is this: Is Heat Death inevitable? If the universe keeps expanding at this break-neck rate won't the maximum possible entropy always be several bazillion steps ahead of the current entropy? Doesn't this render a perfect equilibrium impossible or is my understanding of thermodynamics critically fucked?

[Admiral Valdemar]

There is not enough mass to cause a "Big Crunch" as it is called. The universe will end, as it were, by heat death. That is, the expansion rate will reach a point when the background radiation level is uniform and no energy gradient exists, thus, no work can be done. In other words, the universe dies from a whimper, not a bang or crunch, to paraphrase a certain author.

Your understanding of thermodynamics doesn't seem flawed, but the application of it here is. Basically, entropy will be such that nothing can happen and it doesn't matter if entropy can still increase to a higher amount, there will always be a limit whereby life and certain physical interactions like fusion cannot occur and so the universe is essentially frigid and dead.

[Grog]

I heard somethinga about something called "big rip" as another way the universe could end. Does anyone know how that works?

[The Grim Squeaker]

So the theory that the Universe will eventually crunch and then "bang" again in a different formation is flawed?

[GrandMasterTerwynn]

Okay, I won't even pretend to be well-versed in physics or cosmology, but something has been bugging me. It's well-established that the observable universe is open, right? By that I mean that there isn't enough mass to stop the expansion and cause it collapse back in on itself. Furthermore, something seems to be speeding up said expansion IIRC.

Now my question is this: Is Heat Death inevitable? If the universe keeps expanding at this break-neck rate won't the maximum possible entropy always be several bazillion steps ahead of the current entropy? Doesn't this render a perfect equilibrium impossible or is my understanding of thermodynamics critically fucked?

Our current understanding of cosmology suggests that it is very likely that the universe will eventually become just a collection of stray electrons, neutrinos, and photons of absurdly long wavelength. (Since the black holes will eventually evaporate through Hawking Radiation, and it is believed that protons themselves will eventually decay.) This will represent the universe at its lowest possible energy state. As far as anything interesting is concerned, this marks the end of the universe.

[Admiral Valdemar]

So the theory that the Universe will eventually crunch and then "bang" again in a different formation is flawed?

Yes.

As for the "Big Rip", that depends on whether certain types of Dark Matter and energy exist and in certain ratios.

[GrandMasterTerwynn]

So the theory that the Universe will eventually crunch and then "bang" again in a different formation is flawed?

Yes, the total amount of mass in the universe to provide gravitational attraction is much, much less than the quantity needed to overcome the accelerating expansion. The universe will not come together in a big crunch.

[GrandMasterTerwynn]

So the theory that the Universe will eventually crunch and then "bang" again in a different formation is flawed?

Yes, the total amount of mass in the universe to provide gravitational attraction is much, much less than the quantity needed to overcome the accelerating expansion. The universe will not come together in a big crunch.

Proof of this.

The universe has been estimated to be about 160 billion lightyears wide. However, the universe is 13.7 billion years old, which is also a bit farther back than we can see.

This article generated quite a few e-mails from readers who were perplexed or flat out could not believe the universe was just 13.7 billion years old yet 158 billion light-years wide. That suggests the speed of light has been exceeded, they argue. So SPACE.com asked Neil Cornish to explain further. Here is his response:

"The problem is that funny things happen in general relativity which appear to violate special relativity (nothing traveling faster than the speed of light and all that).

"Let's go back to Hubble's observation that distant galaxies appear to be moving away from us, and the more distant the galaxy, the faster it appears to move away. The constant of proportionality in that relationship is known as Hubble's constant.

"One seemingly paradoxical consequence of Hubble's observation is that galaxies sufficiently far away will be receding from us at a velocity faster than the speed of light. This distance is called the Hubble radius, and is commonly referred to as the horizon in analogy with a black hole horizon.

"In terms of special relativity, Hubble's law appears to be a paradox. But in general relativity we interpret the apparent recession as being due to space expanding (the old raisins in a rising fruit loaf analogy). The galaxies themselves are not moving through space (at least not very much), but the space itself is growing so they appear to be moving apart. There is nothing in special or general relativity to prevent this apparent velocity from exceeding the speed of light. No faster-than-light signals can be sent via this mechanism, and it does not lead to any paradoxes.

From this, we can see that much of the observable universe is already "moving" away from us faster than the speed of light. As we have no reason to assume that gravity operates faster than the speed of light, that means that what we can't observe of the universe, we cannot affect with the gravitational pull of our mass. A further consequence of this observation is that the quantity of the universe we can observe will get smaller and smaller, as the space between galaxies continues to expand, until you reach the point where local gravitational attraction keeping a clump of matter together exceeds the tendency of spacetime to want to disperse the matter. Consequently, in timescales exceeding the remaining lifespan of our Sun, the only part of the Universe a future observer will be able to see is the Andromeda-Milky Way Elliptical Galaxy and its close neighbors.

[The Aliens]

The universe has been estimated to be about 160 billion lightyears wide. However, the universe is 13.7 billion years old, which is also a bit farther back than we can see.

Ridiculous stupid question- does this mean that the universe expanded at some point faster than the speed of light? Is it just the space we call the universe expanding at that rate, or the physical objects in it? If the latter, how can they move faster than the speed of light?

[Zac Naloen]

Ridiculous stupid question- does this mean that the universe expanded at some point faster than the speed of light? Is it just the space we call the universe expanding at that rate, or the physical objects in it? If the latter, how can they move faster than the speed of light?

thats actually answered in his post... read the whole thing this time

[The Aliens]

Ugh, that realy was a blindingly stupid question- my apologies.

[Lord Zentei]

It's answered here too:

http://bbs.stardestroyer.net/viewtopic.php?t=70670

[Shinova]

The universe as we know it is basically the remnants of a giant explosion we know as the Big Bang. My pet theory is that the very edges of this shockwave will eventually collide with that of another universe in space, and the resulting collection of energy gravitates toward itself to become another sphere of energy, where matter and antimatter eventually come close enough to annihilate each other again and create another Big Bang and another universe.

[Lord Zentei]

The universe as we know it is basically the remnants of a giant explosion we know as the Big Bang. My pet theory is that the very edges of this shockwave will eventually collide with that of another universe in space, and the resulting collection of energy gravitates toward itself to become another sphere of energy, where matter and antimatter eventually come close enough to annihilate each other again and create another Big Bang and another universe.

Nopers. The Big Bang was not an explosion of matter and energy into space, it was an explosion of space itself, and matter was carried in it's wake. This is a bit of a simplification as matter/energy determines the geometry of spacetime and thus the rate of expansion, but it serves for the purposes of visualizing what is going on. A typical analogy is that of the baloon being blown into and spots on it's surface moving apart. Alternatively, you can imagine the space between the galaxies becoming "moreish" with time, meaning that the distance between them is increasing even though they are not technically moving apart (as in "they are not moving through space" - it's space that's doing the moving).

Moreover: the Universe is isotropic and homogenous and thus has no center or edges or "shockwave" of expanding matter. Also, with the geometry of spacetime appearing Euclidean, the extent of the Universe is infinite, and as such has no edge.

Follow the link in my previous post on this thread. Read the article.

[The Grim Squeaker]

Thanks for explaining.

So what is the big rip theory in summation? collision with another universe

[Lord Zentei]

Thanks for explaining.

So what is the big rip theory in summation? collision with another universe

That too is explained in the link. And no, given our current standard model the Universe cannot collide with anything, since it isn't moving with respect to anything: the Universe is all there is (though there are hypotheses that invoke higher dimensions that our Universe is embedded in such a manner that it could possibly collide with another universe, but that is not the Big Rip scenario).

We now know that the expansion of the Universe is accellerating. This causes space to expand at an ever greater clip, as well as causing a cosmic event horizon to form at 16 billion light years, beyond which we cannot see. Objects that move beyond this distance will disapear from view and never return. Objects that have a size defined by a balance of forces (such as atoms and planets) will experience a outward tug, causing their size to be increased slightly by a fixed amount that is proportional to the accelleration (think of a weight attached to a spring: the g-force pulls it down by a fixed ammount). A fixed force is added to the balance of forces that determine the size of bound objects, and they reach a new equilibrium and stay there. Moreover our galaxy and it's neighbours will remain gravitationally bound (although in the distant future, space beyond the confines of our intergalactic neighbourhood will seem much emptier than it does now).

However, if the accelleration is increasing with time, this stretching increases steadily too, and as the added outward pull on all objects increases the amount of force nessecary to hold them together increases. This means that eventually galactic clusters will eventually fly apart, then galaxies, then solar systems, then stars, then planets, then people (if they are still around by then), then atoms. Basically, all things are torn apart in a catastrophic End-Of-Time. This is the Big Rip.