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width of the universe
Posted on: Sun, 2006-11-26 21:25
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width of the universe
dose anyone know the width of the universe in light years and by that i meen the 2 furthest things with any matter. Rational Squad Alerts |
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Constantly expanding. We don't even know how far away the farthest object is, cuz we can't see that far.
If current estimates are correct, the universe is about 12 billion years old. This puts the greatest distance between two photons at 24 billion lightyears.
We don't know how fast matter was expanding from the big bang, or for how long the current redshift has lasted and to what degrees. Without this information, it's going to be pretty hard to calculate how wide the universe is.
plus it would change by anywhere up to 6x10^8 every second :)
But basically, it's impossible to calculate, A) because it's constantly expanding at a rapid rate, and B) because we can't actually SEE the farthest objects, or even detect their existence.
Well if we can find a way to detect low-energy tachyons we might be able to detect the existence of objects we can't even see.
Edit: Then, again, if you count low-energy tachyons as matter, the size of the universe is potentially infinite.
Low energy Tachyons? You mean the things that go faster when they lose energy? How would they help us determine the size of the universe? And don't they go back in time at a low enough energy?
Well, the entirety of the universe is definitely finite, it's just... increasing at a large speed, so any determination we could make would A) change immediately and B) be millions of years behind by the time we saw it.
Any detection would take a distinct amount of time, given the long distance.
[quote=JoshHickman]Low energy Tachyons? You mean the things that go faster when they lose energy? How would they help us determine the size of the universe? And don't they go back in time at a low enough energy?[/quote]
No, they don't go back in time at a low enough energy.
They would help us determine the size of the universe because if we could detect them, any tachyon-causing events at the outer reaches of the universe could send some our way. Using the velocity and vector, we could plot a series of rays in space as using the detector as the origin. With a large enough collection of such points, we'd eventually find a point beyond which no tachyons originated, it might appear to form a kind of fuzzy wall of points. From that we could determine the diameter of the "wall" and thus, a rough estimate of the diamater of the universe.
[quote=AgnosticAtheist1]Well, the entirety of the universe is definitely finite, it's just... increasing at a large speed, so any determination we could make would A) change immediately and B) be millions of years behind by the time we saw it.
Any detection would take a distinct amount of time, given the long distance.[/quote]
Which is the reason for low-energy tachyons. They travel faster than light, so with the low enough energies, you'd get almost instantaneous travel. You'd obviously have to factor the energy of the tachyons into the equation to determine how old the data might be, and discard the higher-energy, slower-moving tachyon data and use the low-energy high-velocity tachyon data.
yeah I guess that would work. Except, then you'd have to recalculate it later(unless you propose to find a way to figure out the second derivative of the universes width.
The universe will not be expanding quickly enough to cause a noticable change in the fuzzy wall. Maybe take a new measurement every 2 million years or so and you might see a noticable change...but really...
heh, the question that baffles me is what does that end of the universe look like? And is it a physical barrier?
You just said that when a photon travels somewhere, it expands the universe. There may be a limit to where matter from the big bang has expanded to so far, but there could never be a 'boundary', per se, and it could never be physical.
This seems like Captain Obvious could answer that question!
Well just outside the edge of the universe it's absolutely black, 0 degrees kelvin, density is 0 amus/cubic lightyear...there's just nothing there at all.
Just inside the edge of the universe you'd be able to watch the big bang's first moments, assuming you had sensitive enough equipment and knew where to point it.
On the edge of the universe, you'd see the exact moment the big bang occured.
and if you moved just outside, the very first molecules you moved out would lose all their kinetic energy and heat :), and you'd die Of course, you'd probably be at like 2 K anyways and everything else including yourself and your equipment would be practically dead anyways.
[quote=AgnosticAtheist1]and if you moved just outside, the very first molecules you moved out would lose all their kinetic energy and heat :), and you'd die Of course, you'd probably be at like 2 K anyways and everything else including yourself and your equipment would be practically dead anyways. [/quote]
If you moved just outside the universe...well, you just expanded the universe and changed the rules a little bit. As long as you have a spacecraft to keep you pressurized, you won't lose all your kinetic energy and heat, and you'd still be alive.
How you managed to travel 12 billion lightyears, that's another story.
You would have to do it going faster than the speed of light to catch up to the edge. Also, if tachyons can go faster than the speed of light, then the universe would be bigger than the pulse of light from the Big Bang.
Well, you're operating under a slightly false presumption. It's not that matter is filling up emptiness that was already there and is being filled up through the big bang. The very fabric of space is expanding.
I know it's impossible for me to have gone so far. That's why it's a hypothetical. You take a situation, change one variable, look at the effect, and know the variable did the changing, and nothing else.
Restricting all variables include time. I guess another way would be simply to have the object at the very edge, moving faster than the universal expansion, and that way you avoid the utter weirdness of time-stopping.
[quote=JoshHickman]You would have to do it going faster than the speed of light to catch up to the edge. Also, if tachyons can go faster than the speed of light, then the universe would be bigger than the pulse of light from the Big Bang.[/quote]
I was aware of the former and pointed out the latter in my second post.
[quote=AgnosticAtheist1]Well, you're operating under a slightly false presumption. It's not that matter is filling up emptiness that was already there and is being filled up through the big bang. The very fabric of space is expanding.[/quote]
I thought we were talking about the diameter of the universe, not the expansion of space.
you cannot speak of one without touching the other, as the diameter of the universe/space is not fixed, and thus its expansion is important
Space and the universe are two different things. If you mean a movement of the fabric of spacetime outward from the origin of the big bang, I haven't heard of that. If you're just talking about matter and energy and whatnot moving farther and farther away from the origin, you seem to be making a distiction where none is necessary.
I meant the former. It's not so much that the matter is expanding to fill space, but that the nature of space is expanding. Or at least, that's wha my astronomy book seems to suggest... As I can not observe it in any way, I will trust this authority's view until I can gain better information.
Do you mean that force it is that's pushing the galaxies apart? What exactly does your astronomy book say?
It said
a common misconception about the Big Bang is that matter, cast outward, is expanding to fill the emptiness of space. However, it is more true to say that the very nature of space is expanding.
Or something to that extent.
You'd think they would have mentioned something like that on at least a few of the dozen or so Discovery Channel things I've seen about spacetime and astrophysics.
What is the difference, exactly? We won't stumble upon another universe if we keep expanding. How could you ever tell?
[quote=JoshHickman]What is the difference, exactly? We won't stumble upon another universe if we keep expanding. How could you ever tell?[/quote]
That would be quite interesting if there were two big bangs, far apart, and eventually... boom. Heh, but yeah, I don't see that there is much of a difference outside of semantics. And I'm not quite so sure I believe it.
[quote=Zhwazi]You'd think they would have mentioned something like that on at least a few of the dozen or so Discovery Channel things I've seen about spacetime and astrophysics.[/quote]
yup. I don't actually believe it, at the moment, I'm suspending judgement simply because I know very little of the matter. Plus, it's entirely semantic...
[quote=AgnosticAtheist1]Constantly expanding. We don't even know how far away the farthest object is, cuz we can't see that far.[/quote]
absolutly, there is no fixed size