Register to reply

Where is the center of the universe?

by JediSouth
Tags: universe
Share this thread:
Fredrik
#199
Feb16-12, 07:31 AM
Emeritus
Sci Advisor
PF Gold
Fredrik's Avatar
P: 9,279
Quote Quote by phinds View Post
So, you figure that when folks learned how to sail around the world, and could therefore see more of it, it got bigger?

I think you misunderstand the term "observable universe". It is NOT based on what we CAN see, it is based on what we COULD see, and it is at present 13.72billion light years in radius and if we had the most amazingly wonderful telescopes that could possibly be built, and that could see throughout the electormagnitic spectrum, it would STILL be 13.72 light years in radius.
That's the number of years that the oldest light has been traveling towards us, but due to the expansion of the universe, the actual radius in significantly larger. I don't remember exactly, but I think it's about 45 billion light-years.
phinds
#200
Feb16-12, 07:36 AM
PF Gold
phinds's Avatar
P: 6,135
Quote Quote by Fredrik View Post
That's the number of years that the oldest light has been traveling towards us, but due to the expansion of the universe, the actual radius in significantly larger. I don't remember exactly, but I think it's about 45 billion light-years.
Yes, I agree, and I knew that but got sidetracked by the silliness of the concept of the OU getting bigger because of telescopes so I fixated on the photon age, not the current diameter (which of course IS getting bigger, but not because we have better telescopes)
ynot1
#201
Feb16-12, 08:41 AM
P: 90
Quote Quote by Fredrik View Post
That's the number of years that the oldest light has been traveling towards us, but due to the expansion of the universe, the actual radius in significantly larger. I don't remember exactly, but I think it's about 45 billion light-years.
So our telescopes only show us the universe in its past. Wouldn't it be nice if we could see the present? In fact we're building them right now - the gravitational interferometers. But you say even gravitational waves take time to propagate, so we really couldn't see the present even if we wanted to. Yes unfortunately this planet is being accelerated so we can't see anything in the present. However we sure could see a lot more considering all matter created during inflation is now in gravitational communication since the universe was very small at that time. The trick is when objects accelerate the changes in their gravitational fields propagate only at the speed of light. However note static gravitational fields are in instantaneous gravitational communication.
Cosmo Novice
#202
Feb16-12, 10:14 AM
P: 366
Quote Quote by ynot1 View Post
So our telescopes only show us the universe in its past. Wouldn't it be nice if we could see the present? In fact we're building them right now - the gravitational interferometers. But you say even gravitational waves take time to propagate, so we really couldn't see the present even if we wanted to. Yes unfortunately this planet is being accelerated so we can't see anything in the present. However we sure could see a lot more considering all matter created during inflation is now in gravitational communication since the universe was very small at that time. The trick is when objects accelerate the changes in their gravitational fields propagate only at the speed of light. However note static gravitational fields are in instantaneous gravitational communication.
Yes it would be nice if we could see the present but unfortunately we cant, the Universe speed limit forbids it. There is no such thing as instant gravitational communication on a static field, this is more to do with observation than instantaneous propogation, in fact gravity propogates at the speed of light.

Please see a relevant wiki extract:

The consequence of this, is that static fields (either electric or gravitational) always point directly to the actual position of the bodies that they are connected to, without any delay that is due to any "signal" traveling (or propagating) from the charge, over a distance to an observer. This remains true if the charged bodies and their observers are made to "move" (or not), by simply changing reference frames. This fact sometimes causes confusion about the "speed" of such static fields, which sometimes appear to change infinitely quickly when the changes in the field are mere artifacts of the motion of the observer, or of observation.

In such cases, nothing actually changes infinitely quickly, save the point of view of an observer of the field. For example, when an observer begins to move with respect to a static field that already extends over light years, it appears as though "immediately" the entire field, along with its source, has begun moving at the speed of the observer. This, of course, includes the extended parts of the field. However, this "change" in the apparent behavior of the field source, along with its distant field, does not represent any sort of propagation that is faster than light.
ynot1
#203
Feb16-12, 10:32 AM
P: 90
Quote Quote by Cosmo Novice View Post
Yes it would be nice if we could see the present but unfortunately we cant, the Universe speed limit forbids it. There is no such thing as instant gravitational communication on a static field, this is more to do with observation than instantaneous propogation, in fact gravity propogates at the speed of light.

Please see a relevant wiki extract:

The consequence of this, is that static fields (either electric or gravitational) always point directly to the actual position of the bodies that they are connected to, without any delay that is due to any "signal" traveling (or propagating) from the charge, over a distance to an observer. This remains true if the charged bodies and their observers are made to "move" (or not), by simply changing reference frames. This fact sometimes causes confusion about the "speed" of such static fields, which sometimes appear to change infinitely quickly when the changes in the field are mere artifacts of the motion of the observer, or of observation.

In such cases, nothing actually changes infinitely quickly, save the point of view of an observer of the field. For example, when an observer begins to move with respect to a static field that already extends over light years, it appears as though "immediately" the entire field, along with its source, has begun moving at the speed of the observer. This, of course, includes the extended parts of the field. However, this "change" in the apparent behavior of the field source, along with its distant field, does not represent any sort of propagation that is faster than light.
Good quote. Note static gravitational fields do not propagate.
Drakkith
#204
Feb16-12, 08:14 PM
Mentor
Drakkith's Avatar
P: 11,620
Quote Quote by ynot1 View Post
Good quote. Note static gravitational fields do not propagate.
True, but a static field permits no communication either.
ynot1
#205
Feb16-12, 09:16 PM
P: 90
Quote Quote by Drakkith View Post
True, but a static field permits no communication either.
A logical necessity since if you tried to send some type of gravitational signal you would no longer be a static field. However moving static fields allow the precise determination of their position, mass, velocity, and direction of travel, assuming you can track the magnitude of the field at different positions and times. That way you can get out of the way of that big boy before it comes crashing in. It wouldn't do much good to try and communicate with an asteroid anyway. Note the shape of the object from your perspective, even if it passes, could theoretically be calculated. If the object had spin you could even get a 3d profile. I am wondering if the resolution of the measurements would be limited by the zero point energy on the interferometer reflecting surfaces. I believe there is however a logical question if non-symmetrical rotating objects generate a static field.
Drakkith
#206
Feb16-12, 09:40 PM
Mentor
Drakkith's Avatar
P: 11,620
I'm not sure a massive object coming towards you is an example of a static gravitational field.
ynot1
#207
Feb16-12, 09:45 PM
P: 90
Quote Quote by Drakkith View Post
I'm not sure a massive object coming towards you is an example of a static gravitational field.
If it's not accelerating or rotating I think it would have to be. Else you would have to pick a preferred initial frame of reference (namely yours).
bmehmud
#208
Feb17-12, 12:36 AM
P: 6
Some questions do not have logical answers. We should consider the universe is created as it is and expanding rather considering it originated from a center point. Every point in the universe if a creation point and further looking for logical answers would confuse the physical theories itself.
ynot1
#209
Feb17-12, 12:58 AM
P: 90
Quote Quote by bmehmud View Post
Some questions do not have logical answers. We should consider the universe is created as it is and expanding rather considering it originated from a center point. Every point in the universe if a creation point and further looking for logical answers would confuse the physical theories itself.
Don't forget - those who have all the answers also have all the questions. So further looking wouldn't be helpful.
phinds
#210
Feb17-12, 02:59 AM
PF Gold
phinds's Avatar
P: 6,135
Quote Quote by bmehmud View Post
Some questions do not have logical answers. We should consider the universe is created as it is and expanding rather considering it originated from a center point. Every point in the universe if a creation point and further looking for logical answers would confuse the physical theories itself.
Uh ... HUH ?

Is there any physics in whatever it is you just said?
bmehmud
#211
Feb17-12, 03:12 AM
P: 6
Ok. How this big bang originated. I want a logical answer involving the 'physics' what you know.
Drakkith
#212
Feb17-12, 04:21 AM
Mentor
Drakkith's Avatar
P: 11,620
Quote Quote by bmehmud View Post
Ok. How this big bang originated. I want a logical answer involving the 'physics' what you know.
We don't know. Just like we don't know how to make Fusion power work. Or any of a thousand things we know that we don't know.
We CAN say that the universe was once in a very hot very dense state and expanded outward from there. We can extrapolate back in time to a point very close to where the big bang is theorized to have occurred at, but beyond that we cannot say as our model breaks down.
bmehmud
#213
Feb17-12, 04:32 AM
P: 6
That is not a logical answer not physically proved. You are saying that universe 'WAS' once very hot dense state or we may say 'singularity' BUT from where does the singularity came from? who created the 'singularity' and how this 'singularity' got infinite density? what is density by the way? who created the matter? when the matter was created? giving the accurate calculation time of creation of matter? what is time by the ways? who created the time, space, matter and after all the 'physics' and its principals as we say AND the mother of all questions "How this all is created by itself"?
phinds
#214
Feb17-12, 04:55 AM
PF Gold
phinds's Avatar
P: 6,135
Quote Quote by bmehmud View Post
That is not a logical answer not physically proved. You are saying that universe 'WAS' once very hot dense state or we may say 'singularity' BUT from where does the singularity came from? who created the 'singularity' and how this 'singularity' got infinite density? what is density by the way? who created the matter? when the matter was created? giving the accurate calculation time of creation of matter? what is time by the ways? who created the time, space, matter and after all the 'physics' and its principals as we say AND the mother of all questions "How this all is created by itself"?
YOU ARE NOT LISTENING ... as drakkith pointed out, we don't know. Get over it.
Drakkith
#215
Feb17-12, 05:30 AM
Mentor
Drakkith's Avatar
P: 11,620
Quote Quote by bmehmud View Post
That is not a logical answer not physically proved.
I already answered your question on the origin of the universe. We do not know. The state of the early universe is a much different story. Our current model describes it very well. It is both logical and proven according to current observations. It would be illogical to disregard simply because you don't want to believe it or don't know anything about it.
bmehmud
#216
Feb17-12, 01:19 PM
P: 6
Quote Quote by Drakkith View Post
I already answered your question on the origin of the universe. We do not know. The state of the early universe is a much different story. Our current model describes it very well. It is both logical and proven according to current observations. It would be illogical to disregard simply because you don't want to believe it or don't know anything about it.
Yes I am listening that is why I asked the question. Simply quoting "We do not know" is proving my point here. I want to believe if I get a logical answer. If you do not want to answer is another point. Thank you guys.


Register to reply

Related Discussions
Center of the universe Cosmology 62
Center of the Universe Special & General Relativity 7
The Center of the Universe Cosmology 55