Can We Determine the Center of the Universe Using Comet Orbits?

[shivakumar06]

can we find the center of the universe by measuring the deviation from theoretical value of the shape of comet's orbit when compared to real shape of comet's orbit.

 

[phinds]

There is no center to the universe.

The OBSERVABLE universe has a center, and you are it.

EDIT: you would likely find it informative to read the FAQ in the cosmology section

 

[Hetware]

There is no center to the universe.

The OBSERVABLE universe has a center, and you are it.

EDIT: you would likely find it informative to read the FAQ in the cosmology section

Are we moving relative to the observable universe?

 

[phinds]

Are we moving relative to the observable universe?

Wherever you are, you are the center of the observable universe, so no, we are not by definition.

EDIT: you would likely find it informative to read the FAQ in the cosmology section

 

[shivakumar06]

we know that universe was created after big bang occurred. then the universe would have been a point and started expanding in all direction then it have looked like a spherical ball whose surface is expanding a center. so it is meaningful to talk of center of universe isn't it

 

[Jimmy]

we know that big bang occurred. then the universe would have been a point object. so then the universe would have had a center.

Where's the center of a point?

 

[shivakumar06]

Where's the center of a point?

sorry. i have edited my posting now.

 

[phinds]

we know that universe was created after big bang occurred. then the universe would have been a point and started expanding in all direction then it have looked like a spherical ball whose surface is expanding a center. so it is meaningful to talk of center of universe isn't it

Absolutely not. The big bang was most emphatically NOT a point. It happened everwhere and there is no center and no edge.

This is a bit hard to get your head around when you first hear it, but it is the case. You should read more cosmology. Try the FAQ in the cosmology section.

 

[Chronos]

The premise the universe began as an infinitesimal point is illogical on two counts:
1] If the universe is infinite, it was infinite from the beginning. Only the observable universe would be point-like at its inception.
2] Unless the big bang occurred in some kind preexisting space, the size of a point is undefined in the absence of external spatial coordinates.

 

[phinds]

The premise the universe began as an infinitesimal point is illogical on two counts:
1] If the universe is infinite, it was infinite from the beginning. Only the observable universe would be point-like at its inception.2] Unless the big bang occurred in some kind preexisting space, the size of a point is undefined in the absence of external spatial coordinates.

I agree w/ what you are saying, except that I see the bolded statements as mutually contradictory. If the current observable universe started off as a dimensionless point, then it seems to me that so would have the entire universe. The observable universe likely started off REALLY small, but not as a point. Perhaps that's what you intended by "point-like" ?

 

[litup]

Maybe it would help to think of the universe as a big balloon. Right now we think the balloon is about ~50 billion LY 'across'. Now, going back in time, the universe gets progressively smaller and so does the balloon. The thing is, we have to think of ourselves as being on the surface of the balloon so we don't really have a center, do we? But as the universe goes back further in time, at some point in time it was say, 1 cm across. It is still that same balloon and on the surface that same point looks the same as it does if it is 50 billion light years across, the angles all go out at exactly the same angle from a point on the surface, so it doesn't matter if the universe were one micron across or 50 billion LY across, we are still on the surface so there is no center we can find.

The idea of the balloon shows us the universe has a curvature so if we had a spacecraft that could do say a trillion times the speed of light and travel in what we think is a straight line, we would come back to the same place after X amount of time, whatever that is, say at one trillion c, assuming the universe is actually 50 E9 ly across, we would come back to our solar system in about 20 minutes even though we thought we would be traveling in a straight line. Our straight line is really a very slow curve not even noticeable if we only went from here to the closest star, Alpha Centauri or thereabouts.

 

[Hetware]

Wherever you are, you are the center of the observable universe, so no, we are not by definition.

EDIT: you would likely find it informative to read the FAQ in the cosmology section

I had this conversation with John Archibald Wheeler. How would you determine the center of mass of the observable universe, at least approximately?

 

[Chronos]

I agree w/ what you are saying, except that I see the bolded statements as mutually contradictory. If the current observable universe started off as a dimensionless point, then it seems to me that so would have the entire universe. The observable universe likely started off REALLY small, but not as a point. Perhaps that's what you intended by "point-like" ?

That is essentially the issue addressed by my second assertion. An infinite ensemble of infinitesimal points would collectively, and individually, be spatially undefined.

 

[phinds]

That is essentially the issue addressed by my second assertion. An infinite ensemble of infinitesimal points would collectively, and individually, be spatially undefined.

Ah ... an interesting way to look at it. I had not considered it that way before. Thanks for the clarification.

 

[phinds]

I had this conversation with John Archibald Wheeler. How would you determine the center of mass of the observable universe, at least approximately?

The approximate center of mass of the observable universe is wherever you are. Given homogeneity, I'd say the approximation is quite accurate.

 

[Pasha582]

we know that universe was created after big bang occurred. then the universe would have been a point and started expanding in all direction then it have looked like a spherical ball whose surface is expanding a center. so it is meaningful to talk of center of universe isn't it

Not really. You are imagining the universe as an expanding ball, which is probably in error. The Poincare Conjecture yields possible hints about the topology of our universe. You would be better off imagining our universe mapped to the surface of a ball, like the surface of the earth. Some people used to think Vatican City, Rome, was the center of the world. Others thought it was in Ireland. Bad points could be made for either. If the Earth were a perfect sphere, no matter where you were the horizon would appear equidistant in all directions, giving you the illusion you were at the center. But if you were to travel far enough in a straight line, you would return to your starting point.

The topology of our universe is probably much like that. Also, as the sphere expands, objects appear to recede from you--just as they do in our universe at large. No point on the surface of this sphere may rightly be considered the center. But we COULD possibly use the word "center" to describe a point in time, roughly 13.7 billion years ago...

 

[FreeMitya]

This is a good explanation supplemented with a visual example: (Skip to 8:20)https://www.youtube.com/watch?v=3pAnRKD4raY

 

[phinds]

This is a good explanation supplemented with a visual example: (Skip to 8:20)


https://www.youtube.com/watch?v=3pAnRKD4raY

Nicely done video but I am at a complete loss to see how it has ANY bearing on this thread. What am I missing?

 

[FreeMitya]

Nicely done video but I am at a complete loss to see how it has ANY bearing on this thread. What am I missing?

Admittedly, I was responding less to the original post and more to the first post (your post) about how wherever one is in space, one is always at the centre of the universe, and I thought a visual example of the Cosmological principle would be helpful to laymen like myself. Did you skip to 8:20?

 

[phinds]

Admittedly, I was responding less to the original post and more to the first post (your post) about how wherever one is in space, one is always at the centre of the universe, and I thought a visual example of the Cosmological principle would be helpful to laymen like myself. Did you skip to 8:20?

I watched the whole thing, thought the emphasis on black holes made it irrelevant to this thread even though there was some discussion about the center.

 

[FreeMitya]

I watched the whole thing, thought the emphasis on black holes made it irrelevant to this thread even though there was some discussion about the center.

No worries, it's completely understandable.

 

[Thermate]

There is a set of non-intersecting world lines, each one at rest relative to the the observable universe. In an expanding universe these world lines move farther apart. Relative rest with respect to the observable universe can be determined by measuring the Doppler shift of the most distant radiation sources.

If an observer is moving relative to the center of mass of the observable universe he will observe a blue shift in the direction toward which he is moving, and a red shift in the opposite direction.

I originally stated this with respect to the cosmic background radiation. That statement is probably still valid, but there's a little catch, that I'm not certain of.

 

[Thermate]

The approximate center of mass of the observable universe is wherever you are. Given homogeneity, I'd say the approximation is quite accurate.

Isn't the center of mass the sum of the moments divided by the sum of the masses? Surely that location is not following me around. If I step on the gas, the center of mass of the observable universe is not accelerating with me.

 

[phinds]

Isn't the center of mass the sum of the moments divided by the sum of the masses? Surely that location is not following me around. If I step on the gas, the center of mass of the observable universe is not accelerating with me.

Do you really think your mass, or the distance you can travel, makes anything other than an infinitesimal difference, compared to the mass of the observable universe and the distance from you to its edge? I stand by my statement.

 

[Thermate]

Do you really think your mass, or the distance you can travel, makes anything other than an infinitesimal difference, compared to the mass of the observable universe and the distance from you to its edge? I stand by my statement.

So are you, or are you not moving relative the the center of mass of the observable universe?

 

[Drakkith]

So are you, or are you not moving relative the the center of mass of the observable universe?

Of course you are moving with respect to the center of mass of the OBSERVABLE universe. Just keep in mind that your observable universe changes as you move.

 

[phinds]

So are you, or are you not moving relative the the center of mass of the observable universe?

As Drakkith said, yes you are, but I would add that

1) Your observable universe is being constantly redefined due to motion
2) this is far more due to the movement of the earth/sun/galaxy than to anything you personally can do here on Earth
3) the distance to the edge of your observable universe is about 47 billion light years and all of the motion in #1 is trivial by comparison.
4) Even a much faster motion would not change the fact that the center of mass of your observable universe, due to homogeniety, pretty much follows along with you (the light-cone center is always exactly where you are, by definition)

 

[Thermate]

3) the distance to the edge of your observable universe is about 47 billion light years and all of the motion in #1 is trivial by comparison.

Please provide the sound and valid reasoning that concludes that my observable universe is about 47 billion light years. Does that mean I can see back before the big bang?

 

[Drakkith]

Please provide the sound and valid reasoning that concludes that my observable universe is about 47 billion light years. Does that mean I can see back before the big bang?

That is the radius of the observable universe. The universe has expanded over the last 13.7 billion years and is now the observable universe is much bigger than the 13.7 billion light years one might expect.

 

[Thermate]

That is the radius of the observable universe. The universe has expanded over the last 13.7 billion years and is now the observable universe is much bigger than the 13.7 billion light years one might expect.

This may be some kind of gravitational lensing effect. I will grant that the entire concept of time becomes a bit nebulous in this context; nonetheless, one would expect that the observable universe is no larger than the distance light could travel in the age of the universe.

I am aware that there are three 3-planes of simultaneity with respect to the local universal rest frame. Perhaps one of them will account for your ~47 billion year observable scale. I would like to see your sources on this.