The man’s got simple answers for everything, and a perfect record so far.
You might be thinking about the observable universe, which is not the same thing at all as “the universe”. The observable universe is just the part of the universe we can see. We can see things because light has traveled from them to us. If something is more than 13.7 billion light-years away (ignoring general relativistic effects), its light has not had enough time since the beginning of the universe to get to us. The observable universe is indeed a sphere centered on us with a radius of 13.7 billion light years. But that doesn’t mean the whole universe has a radius of 13.7 billion light years, or that it is centered on us.
No. Wrong. Your belief is contradicted by observational evidence.
If there WERE a center then things would be moving at different speeds depending on how far from it they are it. Farther things would be moving faster, because moving faster would be HOW they had gotten farther away.
But when we look at distant galaxies, they’re all moving away from US. So either the center of the Big Bang is very close to us (in which case we’d have no trouble detecting any remnants) or space is expanding uniformly in all directions and there is no center.
Things are further out because that matter came out of the bang first. It can be the same speed. I say the bang lasted a long time. Since there is a remnant in every other kind of cosmic explosion, I am sure there is one here, and isn’t the search for the missing matter in fact all about finding where it is? They know it is there already, has to be, so start looking for the big bang remnant. It may well not be the center, since the explosion is said to be “lumpy” but it is probably close.
Is this where you’re getting some of your information and perspective. If so, you may wish to at least look here (for balance if nothing else).
Not all of them leave remnants at the site of the explosion. Type Ia supernovae don’t. They leave behind a shell of starstuff that is expanding outward from the site of the explosion at a significant fraction of the speed of light.
If the Big Bang was “lumpy”, why is the cosmic microwave background radiation isotropic to one part in 100,000? And why does the Universe look so much the same everywhere we look?
I hope y’all don’t mind it I piggyback a somewhat related question:
I remember something in my old book about Relativity that I got maybe 12 years ago that there might be a way to find a privileged vantage point, at least when it came to velocity. The idea was that one would alter one’s velocity until the background cosmic radiation was equal on all sides, thus meaning it was not red- or blueshifted.
Is this still considered possible? The stuff I’m reading here makes me think it might not be, but I can’t put my finger on why. I’d appreciate any information you can give. (Remember, this book was designed to explain Special and General Relativity to a layman, so, if possible, try to keep it on the same level.)
I think part of the problem with the misconception is this famous diagram. It looks likes the universe is smaller at the beginning, stays constant for a while, and then starts getting bigger again.
For me, the best way to [try to] picture it is to start with the assumption that the universe is infinite (I know we don’t know that), and then imagine the big bang. If the universe is infinite now, it was infinite at the moment of the big bang. So instead of saying it’s expanding, I like to think of it as simply getting less dense over time. That way of thinking about it probably has it’s own problems, but if I were to draw a diagram similar to the one I linked to, I wouldn’t change the size of the cylinder, I’d keep it the same diameter and just show things getting less dense over time (and forming galaxies, etc).
It also wouldn’t have the problem of looking like a giant condom.
There are also a lot of pictures that show the Big Bang as “seen from outside”, like this or this one. That’s very misleading, because it would have been impossible for anyone or anything to stand outside the Big Bang like that.
[moderating]
Silverstreak Wonder, the General Questions forum is where people ask questions with the expectation that they’ll get factual answers from knowledgeable people. Speculation, guesswork, further questioning are marvelous in MPSIMS, IMHO, and other parts of the Straight Dope, but we’d prefer to keep such things to a bare minimum here in GQ.
Thank you.
[/moderating]
We’ve found the big bang remnant. It’s called the cosmic background radiation. And it is everywhere.
The search for the “missing matter” has nothing to do with the big bang. It might not be matter and it might not be missing, either, depending upon what theories you think are most plausible. If it does exist in the way most scientists currently think, your use of the term is incorrect because dark matter is merely matter that does not glow (or does so very weakly) in the electromagnetic spectrum.
But if there is anything in physics that can be agreed upon, it’s that “matter came out of the bang first” is simply wrong. The big bang is defined as a phenomenon of space-time, not of matter.
Sure, you can do that, but it doesn’t invalidate relativity. Fundamentally, it’s no different from using, say, the Earth as a reference point, like we do every day. You’re just measuring your velocity relative to some large, convenient object. Well, when you zero out the redshift of the microwave background, you’re more-or-less considering your velocity relative to the average of all the stuff in the observable Universe. It’s just another big convenient object, just a much bigger one than the Earth. Also note that, although you can find such a reference frame anywhere in the Universe, it won’t be the same reference frame at every point.
So if she were to wait around long enough, my ex-wife’s ass will literally be ten times as big some day?
Sadly, no. The electromagnetic and nuclear forces holding your ex-wife’s ass together are more than strong enough to overcome the gentle tug of the expanding universe.
Sorry to have stepped out of the thread for a couple days. Other duties. Yadda, yadda. I’ve read all the responses since my last post, twice. And have read all the links at least once.
As a thought experiment, take the Big Bang as having taken place at a point. It doesn’t have to have been a point - it could have been a sphere, a torus or a cigar-shape - but compared to the present size of the universe it might as wll have been a point. From this point (or whatever), the universe expanded to what we have now, of which we can observe only a fraction. From our perspective, it appears the universe is expanding away (with us as the center), but this easily can be (almost certainly is) an artifact. As Krauss illustrates in his lecture, for example (linked above), an expanding universe can look like it’s centered on us, even though it isn’t.
OTOH, it doesn’t follow that there isn’t some objective center to the universe. If we take the location of the Big Bang as zero on an x-y-z coordinate system, everything expands outwards from there. That the universe may be flat spatially in a gravitational sense doesn’t enter into it. Stuff still exists in 3-D space, as in up-down, left-right and front-back. A “flat” universe isn’t Flatland.
Continue the thought experiment and take as our starting point Krauss’ illustration (starting at about 10:00 minutes into the lecture). He gives us a stylized matrix of galaxies, six-by-six as I recall. He then increments the matrix, expanding it down and to the right. And shows, by superimposing T2 over T1, how each galaxy could see itself as center. All well and good. But consider this. If the first galaxy (upper left) were objectively centered, corresponding to a zero x-y-z of the Big Bang, it could be simultaneously true that the subjective sense of centeredness of each galaxy is wrong, yet there is an objective center. Why this is wrong, I must confess, I do not see.
This is something that’s always puzzled me. Given that at one time every piece of matter in the universe was at one point, how can something now be so far away as to be unobservable? Surely it would have had to travel away from us faster than the speed of light?
If I understand correctly, the key is to note that space’s expanding is not equivalent to objects within that space accelerating. They change position relative to each other, but not in a way that counts as acceleration for General Relativity purposes.
But I probably got that all wrong.
Space itself can expand at any speed. The Einstein Constant, or C, applies only to matter.
In order for there to be a coordinate system like that, there would have to be a space “outside” the universe that the universe was embedded within.
But there is nothing “outside” the universe. The Big Bang wasn’t an explosion in space. It was an explosion OF space. Any coordinate systems that you use to measure distance inside the universe was created along with the universe in the Big Bang.
Everywhere in the universe was created at the same time (as far as we can tell) so no location can be treated as “the center”.
This thread’s made me wonder – in a closed universe, where you can get back to your starting point by flying in a straight line at a constant speed (think Asteroids) (I guess this would make it a closed, non-accelerating universe) is there a preferred frame of reference?
It would, eventually, if the dark energy is of the ‘phantom’ variety – and then, it would get infinitely big in a finite amount of time (of course, one could hardly think of it as a coherent whole anymore in this case)! Though you might have to wait for some time for this to happen, far longer in any case than the average ass lasts…