Not that I understood everything I read, but I believe this disproves your relationship between Time and entropy.
Chaos, entropy and the arrow of time
Something bothers me about this, it doesn’t seem to add up properly.
At the beginning of the universe, 14 billion years ago, wasn’t everything very close together? Nothing was 14 billion light years away from us back then. So how come we are just now receiving light from something 14 billion light years away?
This is something that has bothered me for a while now, but I couldn’t find a way to put it into words before I found this thread. I guess I misunderstand something…
Because space is expanding.
When cosmologists try to explain what happened at the BB, it is astonishing how rapidly everything happened. They construct a timeline showing what’s happening every second or so from the start. In a very short time the universe had expanded by a huge amount. By half a billion years, give or take a few 
, it was immense.
Second, you ask how we “just now receiving the light.” We are not receiving it now, but because of Hubble and other powerful telescopes, we are seeing further and further into space. The pictures of these proto-galazies are taken with hugely long exposures through vast clouds of dust and other space debris, and we’ll actually never see the light of these on Earth without such techincal help.
Lemme see…to illustrate, you can, with dark skies, just see the Andromeda Galexy and other “faint fuzzies” that are millions of light-years away (a light year being close to 3 billion years). Other galaxies can’t be seen with the naked eye a’tall, so actually the light hasn’t reached your eyes. With a good telescope, you can begin to see these deep-space objects, because you are penetrating space (which is the same as going back in time).
As one poster noted, it takes light from the sun 8 minutes to reach us. Therefore, the sun you see now left 8 minutes ago. You are looking back in time 8 minutes. OK, the further you penetrate spece with more powerful telscopes, the further back you are going in time, until you get to these places on the other side of the universe, going back, so far, some 13.5 billion years. Hello “space-time.”
That clear it up? Well, this stuff is supposed to make your brain hurt.
It might very well do so but the subject matter is a couple of yards beyond my level. And I guess it depends upon whether or not the universe is a far-from-equilibrium system and that question is maybe 5 yards by me.
No not really. I understand that the light we see from the sun is 8 minutes old because we are 8 light minutes away from the sun. That part is fine.
But the part that puzzles me is the light we see from objects that are 14 billion light years away. So the light we are seeing left that object 14 billion light years ago, and has travelled 14 billion light years to reach us. But the problem is that surely that object would not have been 14 billion light years away from us 14 billion years ago. So why has it taken 14 billion years for its light to reach us?
Also how did it happen that there is a distance of 14 billion light years between us and these objects? Since at the time of the big bang everything was close together that means that these objects have opened a gap from us of at least 14 billion light years in 14 billion years. In other words they have moved at least at the speed of light.
It is so difficult to put these thoughts into words.
I’ve heard a physicist explain that there was no focal point. The Big Bang did not happen somewhere, it happened everywhere.
As a matter of fact objects near the edge of the observable universe are moving away at virtually the speed of light. I think the edge of the observable universe has always been moving at near the speed of light. In fact, as I understand it that is what defines the edge. There might very well be galxies, etc. beyond our observable edge but they are outside of our light cone and we can never see them.
That helps makes sense of it.
This is… well, I’m pretty sure that this is ultimately circular. There are definitely huge gaps in our understanding of the various “arrows of time”.
Actually it was stated that we could see galaxies 13 billion light years away, not 14 billion. If the age of the universe was 14 billion years old, and we could see matter 14 billion light years away, we would be looking at the big bang. That’s kind of an interesting concept really because assuming space is at least as wide as the time it has existed (meaning it has expanded at an average speed above that of light thus far), we should be able to see the big bang in a way. The light would be infinitely red-shifted so we couldn’t actually see it, but the light would be reaching us. And if space wraps like many scientists believe, meaning if you travelled the diameter of the universe in one direction, you’d end up at your original point, then we can see back to the big bang whether the universe is larger than it is old or not. Isn’t that wild? So theoretically we are limited in how far we can look back in time only by how much we can magnify light and how low of frequency we can detect. That’s according to my understanding of it anyway.
The part that gets me is, I hear the age of the Universe given as 14 billion years (or anywhere from 12 to 15 billion). Then the Earth as 4 or so billion, with our Sun at about halfway through it’s predicted 8 to 10 billion year life span.
Yet the Earth is at least 2nd generation matter, as the heavy elements have to come from a super nova. So there had to be enough time for matter to coalesce into stars, which had to go through their life cycle and go super nova, then the matter to once again coalesce into a star with planets and age to 4 billion years.
So adding all that up, looks like that first stars had to form pretty quickly after the big bang, not live very long, or both, to have time to fit all of this into a 12 to 15 billion year window. If the Earth and our Sun are 4 billion, that leaves 8 to 11 billion for the Universe to cool enough for a stars to form (I’m not sure how long it takes a star to form) and those stars to age to super nova (not sure what the average age of first generation stars was/is), and then still have time to form our Solar system plus 4 billion years.
Seems to be cutting it pretty close.
This looks like a pretty decent discussion of the timing of star formation:
First Stars
-I’ll read it once I get some more coffee in me.
Also
Early Stars Show Universe Grew Up Quickly
The First Stars: Stellar Ashes Reveal Timing of Initial Light
Sooner or later we’ll have to come up with a theory where the timing works out exactly right. You can’t cut it any closer than that.
Note that since the BB happened Right Here (as elsewhere) we can look Right Here and see some remnants of it. This is the Cosmic Microwave Background Radiation. However, it’s only 2.7K so not all that noticable. If you look 10 billion light years away, you’ll see the CMBR from 10 billion years ago, and since the Universe was denser and warmer, the CMBR will be a few degrees higher. Still no big whoop. But if you look even farther away, where the distance corresponds to the near beginning of the Universe, then the CMBR starts getting truly hot and the Physics gets interesting (and even bizarre).
Yes, you can look in the immediate vicinity and see evidence of the BB. In fact, the discovery of the CMBR helped move the BB theory up in stature. A couple Nobels were awarded for it. (I’ve personally heard one of the winners give a lecture, but on computer stuff. He should stick to what he knows.)
We now know that the Universe is 13.7 billion years old, to within plus or minus a percent or so. But this was a very recent measurement; up until a couple of years ago, the best estimate ranged from 10 to 20 billion years, so it’s not surprising if anyone remembers a fuzzier figure.
And the key to stellar generations is that big, hot, bright stars burn out far more quickly than do small, cool, dim ones. The Sun will have a total lifespan of about 10 billion years, but a very massive star might only live for a few million, plenty of time for several generations of massive stars before the Sun. Meanwhile, a very small red dwarf might live for hundreds of billions or even trillions of years.
Right. I think maybe entropy wasn’t a good choice for the job. I’ve always looked at entropy as a bookkeeping device that allows the use of the 1st Law in working out thermodynamic problems. I fail entirely to see any practical difference between energy becoming unavailable and its being destroyed. By using the idea of entropy we can say that the total system energy is constant, which is useful, but that some of it is just “unavailable.”
As to circularity. Sure. I think everything we think we know is ultimately based on a few assumptions that can only be proved in terms of each other. Euclid called them “common notions.” The thing to do is just put your head down and keep going. As a homely similie, it’s like a pig caught under a gate. He just squeals like hell and keeps plowing ahead. It ain’t elegant but it gets him where he wants to go. Just call me a cockeyed pragmatist. We need more Oliver Heavisides.
Actually, entropy is quite a useful idea, and very well-founded once you stop thinking about thermodynamics and start thinking about statistical mechanics. Basically, it measures how “big” a region in the phase space of the system is.
For instance, consider two rooms connected by a hall with N gas molecules between them. Also, throw out all the information but which molecule is in which room. That is, the state of a given molecule is in the set {A,B}, and so the space of states is {A,B}[sup]N[/sup]. Now, since the molecules are all the same, the system is symmetric under the action of S[sub]N[/sub] which permutes the molecules.
The entropy is essentially the logarithm (we’ll use base 2) of the size of each S[sub]N[/sub]-orbit. Say N=4. The state (L,L,L,L) is the only state in its orbit, so the entropy is log(1) = 0. On the other hand, (L,R,L,R) “looks like” five other states, so its entropy is log(6).
um, switch “A,B” for “L,R”.
As an informational aside, Hoyle used the phrase on radio and said it was a visual analogy, not derision. See my post here: http://boards.straightdope.com/sdmb/showthread.php?p=6187777#post6187777
How about “Time is Entropy”
rwj