I was reading Time magazine, the recent one about the fate of the Universe. They said a couple interesting things that I didn’t quite understand.
Disclaimer: I was a history major.
One question is whether or not everything is really able to decay. So far, a number of large-scale experiments have been done to determine if protons decay, but no evidence has been found to conclusively prove it one way or the other.
Now if you’ll just be patient I’m sure Chronos will be by shortly to point out why everything I’ve said is wrong.
–sublight.
I happen to pick up the issue of Time the other day.
The article said that the universe will eventually decay into photons, which is a form of radiation and particles like electrons, neutrinos, and positrons.
The universe and everything in it is expanding like a baloon. Not only is everything moving further away from each other, it’s also getting bigger. In a trillion trillion trillion years, the universe will have expanded to the point where an individual atom then will be the size of the known universe know.
So, basically, the universe will go from complete darkeness and emptiness to complete light and fullness.
Then, BANG, it starts over again. Wonder how it’ll be next time around? Exactly the same or wonderfully different… ? I can’t wait to find out.
–Tim
The point of the article is that contrary to what would happen if the universe was closed, there will be no contraction, and no Big Bang again, just eternal blackness.
This has to be the Most Depressing News of All Time.
No, no no! You cannot say that the universe and everything in it is getting bigger. The size of something only has meaning when it is compared with some standard. If everything changes in size, then how would we know? That is, everything changed size as compared to . . . what?
How something decays depends on what it is. The main thing is to keep track of all the conservation laws, and to always decay into less massive things. For instance, there’s something called baryon number which seems to be conserved, and protons are the smallest baryons, so a proton seems to be unable to decay. On the other hand, current theories suggest that baryon number might not be absolute, and that protons can decay, just not very easily. In this case, you’d get a positron, to conserve charge, and one or more photons, to carry off the rest of the energy. The positron, on the other hand (or, equivalently, an electron) can’t decay on its own, because charge is an absolute conservation law, and there’s no charged particles lighter than the electron/positron. The only way to get rid of electrons and positrons is to annihilate them with each other to produce a couple of photons: There’s zero net charge before, and zero net charge after. The photon can’t be gotten rid of at all, permanently, since it’s massless.
So, assuming that the proton decays (because that’s more interesting), let’s look at the ultimate fate of the Universe: Evenetually (after hundreds of billions of years), all the protons decay, and therefore so do all normal atoms (since you can’t have a nucleus without protons). Any neutrons left over from those atoms decay to a proton + electron + antineutrino fairly quickly (about 15 minutes, which is an eternity as particle physics goes, but an eyeblink in cosmology), and the protons formed this way will eventually themselves decay. The neutrinoes left over from this process don’t decay because they’re the lightest spin 1/2 particle, so they stick around, too (it’s possible to convert a neutrino and an antineutrino into a pair of photons, but highly unlikely). Now, most of the positrons produced from proton decay will end up annihilating with electrons, but there’ll be a few electrons and positrons left over that are too far apart to meet (and getting farther apart yet, as the Universe continues to expand). However, the electromagnetic force, like gravity, has an infinite range, so they’ll still interact, if very weakly, across the many light-years. An electron and a positron interacting in this way form what’s called a positronium “atom” (even though there’s no “nucleus”, per se), and there’s no upper limit on how far apart the two particles can be and still interact this way, so atoms billions of light-years across are not out of the question. Aside from those positronium atoms, the only other other particles left will be photons and neutrinoes.
Just because there’s (almost) nothing but light left in the Universe doesn’t mean that it’ll be a very bright place. Even today, photons outnumber all of the heavy particles (heavier than neutrinoes) combined, and the night sky is what most folks would call dark. In the far-distant future, there’ll be a factor of two or three more photons, but they’ll be spread out over a far greater area. Some science fiction writers have supposed that a new Big Bang might arise from the emptiness, but so far as I know, that’s nothing but science fiction: No current theories support that possibility.
So the idea that everything is expanding contradicts the idea that we can measure the expansion via redshift, right? If everything was growing and expanding equally, there shouldn’t be any indication that it was growing (at least not from inside the system). Galaxies wouldn’t be flying away from us at trillions of miles per hour, because the actual miles would be expanding as well. So if spacetime is, indeed expanding, that means that matter which is intricately bound to spacetime is not expanding equally. Is that right? I guess so, otherwise there would be no measurable expansion.
So, has there been any attempt to explain why that should be? IOW, do current theories offer any reason why space should expand but matter in that space should not? After all, matter is part of the “stuff” of the universe. So if the universe is expanding, why isn’t stuff expanding too?
[QUOTE]
Originally posted by Homer
So, basically, the universe will go from complete darkeness and emptiness to complete light and fullness.
[QUOTE]
Actually, just the opposite. Any conscieousness still around would notice that the universe is unbeliveable dark, cold, and empty. And it would be like that into eternity. Kind of depressing, except that it would happen so far in the future that my mind can’t even grasp the concept.
I have no idea. Based on what the article said:
“occasionally, electrons would meet and form atoms larger than the universe is today”.
I kind of assumed that EVERYTHING was expanding. The big bang isn’t like a chemical explosion that spit matter and energy into the universe like grenade shrapnel. The actual universe and everything in it expanded out from it.
So in other words, its not like pool balls moving away from each other after the break. Its like the pool balls are moving away from each other, while the table gets bigger, and the balls get bigger. (I guess. I could be wrong)
But as we know, the balls (galaxies, etc) don’t all move away from each other. If that were the case, galaxies and stars would never collide, and we know they do.
I’m still trying to get my mind around this ‘dark matter’ and ‘dark energy’ stuff. Could someone explain this to me?
My understanding was that the pool table got larger but the balls stayed the same size.
Chronos:
Precisely correct. That is why when I read the TIME article and whenever I read articles or books about the universe I can see only one truth. WE DON’T ACTUALLY KNOW!
Discussing Photons, electrons, and neutrinoes is all fine and well. And research as a whole on the subject says wonderful things about a hominid’s capable intellect. But when I sit outside and look up at the galaxy, and see all the stars and all the space between those stars, my imagination takes over at the very end of my capable intellect. And living in a world with lines, and bounderies it is hard to IMAGINE something without any bounderies, no solid end, ever…infinite…just is…far out!
I’m surprised that DrMatrix and Chronos haven’t jumped on this yet! 
The universe is expanding but the “stuff” does not. This is because the expansion of the universe is “weak” in that it is only significant over vast distances. The expansion is measured on scales of millions of trillions of miles. Forces such as gravity, atomic bonds, etc. can overcome the expansion of space and keep stuff together. So an atom does not expand with space. Neither do people, planets, stars, solar systems, galaxies, or galaxy clusters. The expansion of space occurs in the vast empty spaces between galaxies/galaxy clusters.
No…what Chronos said.
Quoth Phlosphr:
Well, yes, but only in the sense that we don’t actually KNOW anything. Do I know, for instance, that I have brown hair? Maybe my mirror is actually a complicated TV screen, showing somebody else’s image. Maybe I’m hallucinating. Maybe the aliens are controlling my sensory systems in some sort of weird experiment. However, based on the available evidence, the simplest and most likely explanation is that my hair really is brown.
Similarly, we can make all sorts of observations of nature, and from those observations, deduce the simplest and most likely laws which govern nature. Admittedly, there’s a lot more evidence for my hair color than there is for, say, proton decay, or the various models of the Big Bang, but there’s no qualitative difference between the deductions made.
Meanwhile, we had a great discussion of the expansion of the Universe a while back in this forum: An expanding universe? Am I expanding?
There’s only light if there’s something to perceive (as in, reflect, refract, absorb, infer, understand, any of the above) the light. With an empty Universe there is nothing to perceive the light except itself. So it can be as bright as it wants, but it’s still gonna be dark, which means that at that point there becomes no distinction between light and dark… right?
So, dark, cold, empty… kinda like the Universe (for lack of a better term) before the Big Bang. But it’s not going to go KABLOOIE! this time, huh? Says who? The same perturbations in the field (what field? Hell if I know. There can’t be a field if there’s nothing to construct or regulate that field) that caused the Big Bang could conceivably reoccur once conditions are returned to the original state. Something from nothing… ? In a totally static system, the slightest, tiniest, littlest change echoes throughout the entire field, like ripples in a still pond. While the pond thrashing about with waves and crashing breakers, these changes mean nothing. But let it get still, and the smallest whisper of air disrupts the whole system. Add one to one? Shit! You just doubled it! Add one to twelve quadrillion… big damn deal. “1” is not a large number, but it has dramatic changes depending on the size of the system in relation to the size of the number. Everything is relative.
Sorry guys, but seeing as how everything else seems to be cyclical in nature, I have a hard time accepting that the Universe isn’t either.
For lack of a better analogy, think of the wavelength of light… we can start at a wavelength of planck length, the smallest wavelength possible, right? Even if I’m wrong, the true smallest wavelength is inconsequential, so keep with me here. The wavelength gets larger and larger and larger until it’s length is so great that it is indistinguishable from a straight line (whether it curves to gravity is inconsequential for the analogy, also). At this point, this wavelength has grown so massive that it ceases to exist as a wavelength, and any tiny perturbation in it becomes the reality of the wavelength. Cyclical.
Burn me down, smarties. I’ve said it before and I’ll say it again: I don’t know what’s right until I know what’s wrong. And I like to know what’s right.
–Tim
Homer, I like your last couple of lines, you sound like a person who is quite a philosopher, someone who exhibits a rare equanimiity.
Do I have proof of the Big Bang? nope
Does Steven Hawking have proof of the big bang? nope
No one truely knows WHAT happened, or is happening. Yet our intellect has enabled certain people to understand the laws of the universe better than others. And Humans as a whole, the primate Hominid has exhibited amazing leaps when it comes to understanding the structure of the universe as we perceive it. From inventing machines that can see millions of miles past our little planet in this little gallexy in this universe, to seeing miniscule microbes that make up a bacterium. Infinitely small and infinitely vast, can we truly understand a universe with no boundery? none.
We have to right? I like to know whats right as well. but this is a aspect of existance I’m not completely sure we can understand. I know we can infer…but can we truly understand whats right when it comes to the universe.
I thought I had read somehwere that the Big Bang alternative was a quantum bubble, and that Hawking (IIRC) had shown that a quantum bubble like this would have no singularity at the begging (hence no big bang) nor one at the end.
Was this just playing with figures but ignoring facts?
Not sure. But if an atom a trillion trillion trillion trillion trillion years from now is the size of the current known universe, then the balls must be expanding too.
Maybe someone who really knows quantum physics or astrophysics or something can put this one to rest.
Homer - Your ‘if theres a light in the universe and no one is there to see it’ post raises an interesting point. But take it a step further. If an empty void of a universe is there and there is no consciousness there to percieve it, does it even exist?
Although since the universe presumably existed before sentience, I don’t know if that reasoning is sound.
Any expansion must be measurable. If universe is expanding and everything in it is expanding at the same rate this would not be measurable. Something that cannot be measured does not exist. “An expansion which cannot be measured” is a meaningless expression.
I’m surprised no-one’s pointed out the discussion of this very point we had in this thread: Obscure sci-fi story: ‘Is there a way to reverse entropy?’