Physics

[lostsheep]

I have a question about relativity. I was reading a book about physics for laypersons, and it seemed to be saying that light from our planet in the future could be reaching some other planet in another part of the galaxy, depending on relative motion...or we could be getting light from the future from some other part of the galaxy, or something like that. I'm obviously very confused.

Also, I have another question: if the universe expanded from a central point, then why do we see residual radiation in all directions? Shouldn't it just radiate from the center point?

[PanAtheist]

lostsheep wrote

if the universe expanded from a central point, then why do we see residual radiation in all directions? Shouldn't it just radiate from the center point?

I hear that the universe expanded like the surface of a balloon expands.
It's every point moving away from every other point.
Hence radiation everywhere.
Exactly what that "balloon-like" expansion is in reality, I have no idea.

[lostsheep]

PanAtheist wrote

I hear that the universe expanded like the surface of a balloon expands.
It's every point moving away from every other point.
Hence radiation everywhere.
Exactly what that "balloon-like" expansion is in reality, I have no idea.

That helps, actually....I think. So then, if you look from our earth in every direction, then is the edge of the universe equal distance away in all directions, or is it infinite in all directions...does that even make any sense?

[Choobus]

You have to ask yourself what it means for the universe to be expanding. It's not some 3D object getting bigger with respect to some reference frame. The universe is the reference frame (this is why relativity seems weird, and why the statement about future light from earth is incorrect, or at best improperly defined). As pan asshole says, the expansion of the universe does indeed involve every point in spacetime moving away from every other point (at least on a large enough scale. On a quantum scale it's all over the place).
That's why there is no edge or preferred directionality.

[Choobus]

HEre are some links that explain things better than I can be bothered to


http://cosmology.berkeley.edu/Educat...ng_Primer.html


http://www.cseligman.com/text/galaxies/universe.htm

http://www.grc.nasa.gov/WWW/K-12/Num...e_UNIVERSE.pdf

[lostsheep]

Choobus wrote

HEre are some links that explain things better than I can be bothered to


http://cosmology.berkeley.edu/Educat...ng_Primer.html


http://www.cseligman.com/text/galaxies/universe.htm

http://www.grc.nasa.gov/WWW/K-12/Num...e_UNIVERSE.pdf

Thanks, I am going to check these out.

lostsheep wrote

I have a question about relativity. I was reading a book about physics for laypersons, and it seemed to be saying that light from our planet in the future could be reaching some other planet in another part of the galaxy, depending on relative motion...or we could be getting light from the future from some other part of the galaxy, or something like that. I'm obviously very confused.

Also, I have another question: if the universe expanded from a central point, then why do we see residual radiation in all directions? Shouldn't it just radiate from the center point?

Yes. As of today, if there were intelligent beings located near Proxima Centauri, they would be seeing our planet 4.22 years ago. If today we looked in a telescope and saw a giant "we iz here" sign from a planet next to Proxima Centauri, we would be viewing that sign as having it been shown in March of 2005. If we erected a giant sign that said "we iz here" today, then the inhabitants of said planet wouldn't see it until July of 2013.

lostsheep wrote

That helps, actually....I think. So then, if you look from our earth in every direction, then is the edge of the universe equal distance away in all directions, or is it infinite in all directions...does that even make any sense?

It is infinite in all directions, but that doesn't mean we're at the center of it. Keep in mind that at this very second, if we look at the furthest in distance galaxy from us, we are looking about 46 million years in the past. Between then, and now, the universe has grown an incredible amount.

[lostsheep]

stavinggrace wrote

Yes. As of today, if there were intelligent beings located near Proxima Centauri, they would be seeing our planet 4.22 years ago. If today we looked in a telescope and saw a giant "we iz here" sign from a planet next to Proxima Centauri, we would be viewing that sign as having it been shown in March of 2005. If we erected a giant sign that said "we iz here" today, then the inhabitants of said planet wouldn't see it until July of 2013.

lol (we iz here)

Okay, I get that it takes a while for the light to get here, but the book I am attempting to read seemed to be saying that due to relative motion there were (relative) time shifts, so light that hadn't occurred yet here could be on its way to somewhere else...or something like that. However, Choobus said this was incorrect, or that I just misunderstood. I am going to re-read that section again...then I may ask another question.

[lostsheep]

stavinggrace wrote

It is infinite in all directions, but that doesn't mean we're at the center of it. Keep in mind that at this very second, if we look at the furthest in distance galaxy from us, we are looking about 46 million years in the past. Between then, and now, the universe has grown an incredible amount.

Thanks. I did begin reading the links Choobus sent, and it's helping sort of I think. So, since you seem to understand this stuff, I have a question: is the background radiation that we see the same at every part of the universe then? I mean, if we went to Proxa Centuri or some other galaxy would the background radiation appear the same? I am guessing yes, since we see the big bang all radiation all around us in all directions. So is every part of the universe the center then?

[Choobus]

stavinggrace wrote

It is infinite in all directions, but that doesn't mean we're at the center of it.

Says who?

stavinggrace wrote

Keep in mind that at this very second, if we look at the furthest in distance galaxy from us, we are looking about 46 million years in the past. Between then, and now, the universe has grown an incredible amount.

46 million years? That number still has traces of shit on it, having been pulled right out of your arse.

lostsheep wrote

Thanks. I did begin reading the links Choobus sent, and it's helping sort of I think. So, since you seem to understand this stuff, I have a question: is the background radiation that we see the same at every part of the universe then? I mean, if we went to Proxa Centuri or some other galaxy would the background radiation appear the same? I am guessing yes, since we see the big bang all radiation all around us in all directions. So is every part of the universe the center then?

The "center" of the universe is just relative to where you're standing. No matter what part of the universe you look from, space is expanding outward, in all directions, so you're always at your "relative" center of the universe. The most common argument to this is "well, if everything's expanding outward relative to where you are, then how can the Milky Way possibly collide with Andromeda?"

Answering that question kind of makes it all easier to understand. Our galaxy is going to collide..or really rather..."mix" with Andromeda in about 3 billion years. The space between these two galaxies is constantly expanding, but the gravitational force between these two galaxies is overtaking the expansion of space. The distance between us should be increasing, but gravity is not only not letting that happen, it's doing the opposite.

Just remember that two given stars aren't moving away from eachother, they're not moving away from anything, it's the expansion of space all around them that's creating the change in distance between the two. (And even that is relative to how you measure the distance.) Relativity takes a long time to understand.

Choobus wrote

Says who?

Which part?

Choobus wrote

46 million years? That number still has traces of shit on it, having been pulled right out of your arse.

Apparently my head was entirely up my ass when I wrote that. "Million" should be "billion". The edge of the observable universe is 46 billion light years away. I'm sitting here trying to think of why I would write that the light would be that old...and I don't have a clue. Having your head up your ass can do numbers on your ability to use logic I suppose. Hey, at least I didn't really fuck it all up and say there was a god.

[Philboid Studge]

stavinggrace wrote

Apparently my head was entirely up my ass when I wrote that. "Million" should be "billion". The edge of the observable universe is 46 billion light years away.

Verily the ass you pull facts from is a goatse'd black hole and font of misinformation.

[Choobus]

stavinggrace wrote

Apparently my head was entirely up my ass when I wrote that. "Million" should be "billion".

That's wrong as well since the universe is less than 15 billion years old.

It's almost as if you don't know what the fuck you're talking about.