Question for the physicists

Discussion in 'Off Topic Area' started by benkei, Jul 21, 2011.

  1. benkei

    benkei Valued Member

    Hi guys, got a question after a show I watched the other day. I have a bit more than a layman's knowledge of physics (went up to first year university level) so feel free to get a little complicated if you wish.

    It was a show about the universe, and the narrator was going through to the end of what we will know as time. All the stars will have died and the universe will be cold and time will essentially have stopped because the universe will have reached the end point of disorder. Here's where I have a problem.

    If energy is constant and cannot be created or destroyed, then how can the universe reach an "end state" as it were? If all the stars have died, shouldn't there be a collapsing of the universe into another possible big bang because the universe cannot sustain its size (which in effect, correct me if I'm wrong, would still be energy at work)? How can the universe just "die", it doesn't seem (to me at least) to fit with the 1st law of thermodynamics......
  2. SpikeD

    SpikeD At the Frankenstein Place

    *No Expert here*
    If you are referring to entropy, i think it means ( in the scenario you present) that the energy is distributed evenly throughout the universe (which will be x amount of tines bigger than it is now) so not lost just really far apart. As for a contraction event, the show i saw recently regarding this was a little hazy on the details about this but essentially the current accepted model suggests an infinite expansion; however there are many conflicting arguments, some claiming that the dark matter in the universe will allow for a contraction event and re-start the big bang process.
  3. LilBunnyRabbit

    LilBunnyRabbit Old One

    Think of it this way - I have a big room with several candles burning. The room is completely sealed (even in terms of energy leaks) and there is enough oxygen for all the candles to burn down.

    To start with there are concentrated points of energy (the candles/stars). Eventually they burn down. The energy has not vanished, but the average temperature of the room has now increased (not by much - it's a big room and there's not many candles).

    The energy from the candles is now spread evenly through the room, as is the matter (mostly). This is the point of maximum entropy. Without an outside input of energy then this end state will remain steady.
  4. CosmicFish

    CosmicFish Aleprechaunist

    Not a physicist here, either, but I'll have a stab. Bear in mind also that not only is the universe expanding but at this point it's believed that the expansion is accelerating. LBR's analogy is a good one. Take that and imagine that the room is also, somehow, getting bigger and bigger and that the candles are getting further apart as they slowly burn out. So if this prediction of the "end" of the universe is accurate, then all the energy of the universe will still be there, but it will be spread out over an inconceivably huge area.

    Re: the re-collapsing universe. If I understand it properly myself, in order for that to not happen all you need is for the initial expansion to be more powerful than the overall gravitational forces. Imagine the difference between a rocket that shoots into the air but falls back to earth and a rocket that shoots into the air with greater than escape velocity - therefore escaping the Earth's gravity well and disappearing off into space forever.
  5. benkei

    benkei Valued Member

    Thanks guys, makes sense now! Scary thought tho, kinda depressing when you think about it
  6. LilBunnyRabbit

    LilBunnyRabbit Old One

    Less scary when you consider the timescales involved, also less depressing when you consider how quickly our understanding of these things progress. It's always possible that we'll find a way to cheat it eventually, if we survive long enough.
  7. SpikeD

    SpikeD At the Frankenstein Place

    Agreed, the show i saw mentioned something like 10 to the power of 98 years till the last blackhole evaporates/destroyed
    14 to the power of 9 is the current age of the universe. Life will obviously cease way before then though.
    Last edited: Jul 21, 2011
  8. Kwajman

    Kwajman Penguin in paradise....

    We'll long be fossils by the time this even begins to happen.
  9. Mitch

    Mitch Lord Mitch of MAP Admin

    It will never happen because long before then the four Alpacas of the Apocalypse will have let loose Llamageddon.

  10. m1k3jobs

    m1k3jobs Dudeist Priest

    If it was the same show that I was watching one theory stated that at the end point each individual photon will so far from anything else that they will have nothing to react with. At such a huge scale the laws of physics break down for that photon and time ceases to exist and the mass of the photon become infinite. It will then be the seed for a massive expansion (big bang) into a new universe.
  11. AZeitung

    AZeitung The power of Grayskull

    Ehhhhhhh. . . that doesn't sound right. Are you sure that show wasn't "Doctor Who"?
  12. Hanwei

    Hanwei Valued Member

    The acceleration of the universe' expansion is caused by dark energy, and no, i am not making this up. Only six or seven percent of the universe' mass is in the known universe, a further .7% is made up of neutrinos, and another 27-ish percent is dark matter. The remaining percentage of the universe' mass is dark energy.

    This dark energy causes the universe to expand for reasons unknown. Theoretically, at one point in the far (really far) future it will rip apart the atoms themselves. Though by that time the sun will have destroyed earth in its expansion to a red giant, so we wouldn't even be fossils. More like space-dust.

    As for the conservation of energy issue, it's like trying to heat your house with centralized heating vs. trying to heat the earth with your centralized heating. The energy is still there, but it's very very spread out.

    If you want to know more check the science channel website, this is just written off the top of my head.
  13. AZeitung

    AZeitung The power of Grayskull

    I think you mean "is visible matter" (edit: by that I don't mean "within the visible universe" but "gives off electromagnetic radiation")

    That's not quite true. By Einstein's equations, energy and curvature are related. By making measurements that allow us to deduce the rate of expansion vs. time, it can be shown that the rate of expansion increases vs. time, thus implying an overall negative curvature to spacetime. This leads to the CONCLUSION that the energy density of the universe is negative (with little positive energy bumps where matter is present).

    The reason that dark energy causes the universe to expand is only a mystery to the extent that the fact that positive energy causes gravity is a mystery. Dark energy is a conclusion based on measurements of the expansion of the universe, not a thing we observed and then later found to cause the universe to expand. So it's not surprising at all that dark energy causes expansion, since it was thought up specifically to explain it.
    Last edited: Jul 23, 2011
  14. righty

    righty Valued Member

    Is it a sphere?
  15. AZeitung

    AZeitung The power of Grayskull

    Well, now you're basically asking "is it a cow"?
  16. Fish Of Doom

    Fish Of Doom Will : Mind : Motion Supporter

    the answer is yellow.
  17. righty

    righty Valued Member

  18. LilBunnyRabbit

    LilBunnyRabbit Old One

  19. brotherinarms

    brotherinarms Valued Member

    no-ones ever seen dark matter but we believe it exists. it has the opposite effect of gravity instead of pushing down it pulls up, in space instead of pushing together it pulls away.

    everything is theory at the moment, apparently now scientists have discovered/ are trying to prove that the big bang was not the start of our universe instead every trillion years or so two flat membranes/brains collide "rebooting" each-others "dead" universe and also rather than having 4 dimensions (2 parallel universes, dimension of time and the dimension of space) their are TWELVE... although its interesting we still know less about our solar system and its stars and planets not to mention the oceans on our planet. baby steps people!!

    i think a dead universe has energy just not the capable environment for life.
  20. LilBunnyRabbit

    LilBunnyRabbit Old One

    Not quite - dark matter is just matter we haven't been able to detect so far - it doesn't do anything strange with gravity. There's other theories about the repulsion.

    This is theoretical work - they're just putting together models which explain the things we see, but this isn't the same thing as trying to prove them. There are many different models which could explain the universe as it exists (or as we perceive it existing) but we currently don't have much evidence to select between them.

    Again, this is just to make the mathematics work - there's no actual evidence either way that there are any particular number of dimensions (although without at least twelve, many of the current mathematical models break down).

    A 'dead' universe is cold, at the highest possible level of entropy it can reach, nothing but sparsely populated particles moving sluggishly around a potentially-infinite expanse of space. Life in a universe is a somewhat different matter, but there we get even more speculative than we have so far.

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