they say.. (I believe it is from a brief history of time. SH) Time started with the Big bang, the universe expands, it gets to a point where it no longer expands then begins to collapse (yes, I know, just one theory) at this point some claim that Time will reverse, that it will go backwards. (please help me fill in the blanks here) first question is, How can time flow backwards? second: I just watched a movie (Mr. Nobody) which at one point it explained that a cigarette cant be unsmoked, that the carbon molecules cannot go back into the cig and reconstitute the cig. but wait! what happens to that carbon after it leaves the cig? It floats around and gets absorbed back into the ecosystem, which given the right circumstances, could be absorbed back into a tobacco plant, in essence reconstituting the cig. so other than argueing its a bad analogy, time is running in reverse right now..?
This is an improper and unscientific use of the word "theory," but it's the scientists' error, not yours. This should be called a hypothesis. A hypothesis does not get promoted to being a theory until it's been proven true beyond a reasonable doubt. That's a new one for me. Who are these "some" who make this claim??? Quick answer: it can't. Several other features of the universe would have to also be modified or reversed before that could happen. No. On a micro scale, sure, it looks like the carbon atoms are going in a loop. And on a micro scale, they are! But on a macro scale (looking at the entire universe rather than a tiny portion of it on one little planet), there is no loop. Every time the carbon is burned, its atoms combine with oxygen atoms and this releases energy. The movie failed to address the issue of entropy. The system of the cigarette starts out with great organization (all those complicated organic molecules in the tobacco and the paper) but as it burns it becomes simpler (all that matter is reduced to carbon dioxide and water and a few other fairly simple molecules). In order to get that ultra-simple carbon dioxide back into a form that can be smoked, something has to happen that increases the organization of that region of space. That "something" is life, specifically plant life. Plants perform photosynthesis, breaking down simple carbon dioxide and oxygen molecules, and reassembling their elements into much more complicated molecules like proteins and carbohydrates. The only way they can do this is to extract energy from their surroundings and utilize that energy on a micro level to turn small molecules into large ones. This energy comes from the Sun (in our solar system--but other solar systems will be found to work more or less the same way). As the Sun continues to radiate energy, it cools down, and eventually it won't be hot enough to work anymore. At this time (about 5B years from now, so don't lose a lot of sleep over this) it will become a red giant, becoming enormously larger but cooler. Eventually it will burn out completely. When all the stars in the universe burn out completely, the universe will reach a state of maximum entropy and there will no longer be any organization so there will be no more life. And no more cigarettes. Please Register or Log in to view the hidden image! If it were truly possible for time to flow backwards, this would be a violation of the Second Law of Thermodynamics, which tells us that entropy tends to increase over time. Temporary reversals are possible (such as the existence of life) but these are more-than-balanced by an increase of entropy in nearby regions (living things using up a lot of solar energy, making the universe cooler). If the universe could continue to become more organized, this would mean that entropy had been reversed on a macro scale. This is impossible in our universe because our universe dutifully obeys the Second Law of Thermodynamics. There are two possible endings to our universe, depending on how much Dark Matter and Dark Energy it contains. 1. It will continue to expand from the inertia of the Big Bang. This will dissipate all of its energy as the temperature everywhere falls closer and closer to Absolute Zero. 2. It will run out of momentum and begin to contract back in on itself. Eventually all of its matter and anti-matter, energy and anti-energy (forgive me if my terminology isn't quite right) will collapse and combine, forming zero matter and zero energy. At this point whatever is left of the universe will be exactly the same as it was before the Big Bang: just a whole lot of nothing.
Something can cycle back and forth, even with time moving only forward. For example, say I have a large balloon, which I am filling with hot air. This causes the balloon to expand. Once fully expanded, I stop adding hot air and let the hot air cool back to room temperate. The balloons start to shrink. Time only moves forward, via two different events one for expansion and one for collapse. With the big bang, we begin with a rapid event. If and when this reverses back to this small state, the final event will happen slowly, since the original built in mass/energy will have been used up for other purposes, with much of this energy lost into entropy. It may cycle, but not as a mirror image.
You're not looking at the big picture. It takes energy to heat the air. That energy has to come from somewhere. With every hot-air/cool-air cycle, you are losing a little bit of energy and increasing entropy.
#1 seems more logical to me, I can see the universe running out of momentum, but unless acted on by an external force, it couldn't begin to collapse.
If time were going backwards, it would not seem so to the sentient beings or animals involved; it would seem normal and natural. So how do we know we're not in the reverse bang already? And if it seems like forward motion to everyone involved, perhaps then it virtually is forward motion. Perhaps then, forward, backwards, it makes no real difference. It's like the title of that old Clint Eastwood movie, 'Every Which Way But Loose'.
IF, is what we are talking about. personally I don't believe it is possible, but also I think it would make good conversation. if time were to reverse and go backwards it would mean that the law of time has been rewritten, if one law can be rewritten, then its not a stretch to assume others can be rewritten also. so the second law would be entropy DECREASES over time,
I does make good conversation, but so does talking about girls food (just an example, lol). But before we give much play to rewriting the laws of nature, could we at least exhaust the more plausible ways that entropy could be defeated. The unlikely collapse/bang/collapse/bang scenario itself is generally considered to merely push out the timeframe before compete entropy occurs, because it is believed that each cycle would fail to pull back all of the EM released by the previous cycle. Eventually the final crunch would not have enough matter/energy to bang. Would it be easier for you to imagine that type of repeating collapse/bang scenario than to imagine a scenario of an infinite and eternal universe where entropy is defeated by big bangs across the landscape of the greater universe? Just asking, because one plausible alternative to the cyclical universe seems to me to be that of big bang parents (mature expanding galaxy filled arenas that would be common throughout the greater universe) merging to produce a new "infant" big bang, where each mature parent big bang arena contributes part of its galactic material to the new big crunch, instead of the crunch having to reach out and pull in all of the matter and EM that has escaped out into the far reaches.
Not quite true, in that in some scenarios the internal gravitational pull of all the matter will be sufficient to cause the universe to collapse in on itself. This does not need external forces, just internal. If you consider as an example the system of a person standing on a planet, throwing a ball in the air. The system imparts energy into the ball, it moves away from the surface of the planet, eventually losing momentum and falling back down. It needs no external force as, in the example, gravity is internal to the system. In a simplistic form, this is one scenario for the fate of the universe: the Big Crunch.
if you were on a satellite( at the Lagrange point?) and threw the ball into space, it would keep going, granted there is a chance that gravity from other sources could bring it into an orbit, but if there is no source nearby it would keep going unless acted on by an external gravity source, at the end of the universe those sources would be few and far between. the premise of the collapse assumes that gravity doesn't decrease over distance, that there is always a 'connection' between bodies. where is the voyager probe? still going away from us, correct? so the earths gravity no longer has an effect on it, correct?
a ball thrown from a lagrange point would orbit the Sun, or the Earth, or the Moon depending on which lagrange point and the speed of the ball and its direction. it could also crash into any one of them or leave the solar system entirely. gravity works out to "infinity", though would be "infinitely" weak there. the premise of the collapse is that gravity will over time stop the expansion and the universe will then begin to collapse. this premise has gone out of favour with the discovery that the expansion, due to dark energy, is accelerating.
and where has this em escaped to? if this scenario is to be plausible then all the stuff in this universe now will always be there for the next cycle. it can't leave this universe.
a theory is just the model that best fits the data. theories aren't proven and in fact that would exclude them from being theories. and reasonable doubt is ok for the courtroom.
The problem is that each cycle gets longer and longer, in theory, due to the fact that entropy of a closed system continually increases. This is the Wiki: http://en.wikipedia.org/wiki/Cyclic_model There are other cyclical models, and though the hypothesis that I suggested isn't cyclical, it does require an infinite and eternal open universe with infinite energy to hypothetically defeat entropy; its just talk.
Sure, there are examples where one can overcome the local forces such that one is no longer affected by them, but the Big Crunch model suggests that the universe might not one of them, that gravity will eventually pull everything back together. Of course, this is just one proposed model, with the other prominent one being the Big Freeze. The Big Crunch is a recognised model, but of course there are still lots of unknowns, most notably how dense the universe actually is, given that much/most seems to be dark matter or dark energy. If the universe is denser than the critical density threshold then it will collapse in on itself. Otherwise it will remain open, either expanding forever, or at a rate that approaches zero.
This is not actually the case. If the universe has a collection of normal matter and energy in it, then it will collapse if it has above the critical density. If the universe has a strong enough cosmological constant and/or enough dark energy, then the universe can have an arbitrarily high density relative to the critical density and continue expanding forever. The critical density still controls overall geometry.
Cheers... I knew there was something I was missing even as I wrote it, as my explanation wouldn't account for the crunch of an open universe or the continued expansion of a closed one, which are possible alternative scenarios. Please Register or Log in to view the hidden image!
Yeah, the cosmological constant throws a big wrench in the works. I forgot that if it has a high enough negative value, you could get an infinite universe that still collapses.
