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

[phinds]

This may be some kind of gravitational lensing effect.

HUH? I'd say you don't understand gravitational lensing. Certainly it has nothing to do with this discussion.

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.

If the universe were totally static, you would be rigth, but it isn't, so you are wrong. It's expanding.

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.

I have no idea what you mean by this. As for a reference of the 47 billion years, get any Cosmology 101 text.

 

[Thermate]

HUH? I'd say you don't understand gravitational lensing. Certainly it has nothing to do with this discussion.


If the universe were totally static, you would be rigth, but it isn't, so you are wrong. It's expanding.


I have no idea what you mean by this. As for a reference of the 47 billion years, get any Cosmology 101 text.

Please provide a specific reference. ISBN and page number.

 

[Thermate]

OK. I see cosmology has finally caught up with what I was saying decades ago. You are talking about the Universe as treated as simultaneous with the local center of mass of the observable universe. Congratulations to the scientific community! You finally caught up with a high school dropout. As I said, this is a "lensing" effect. One plane of simultaneity is the time that all observers will agree upon when they look at their watches and measure their own time lines relative to the big bang.

 

[Thermate]

HUH? I'd say you don't understand gravitational lensing. Certainly it has nothing to do with this discussion.

Really? Has the global curvature of the universe changed in the past 13 billion years?

If the universe were totally static, you would be rigth, but it isn't, so you are wrong. It's expanding.


I have no idea what you mean by this. As for a reference of the 47 billion years, get any Cosmology 101 text.

Another second plane of simultaneity is what actually hit's our eyes. The further back in space you look. the further back in time you see.


Those are the easy ones. Sorry. I can't give you a reference on this, because I only have it as an immediate thought. I don't know that it is written down anywhere.

 

[marcus]

Please provide a specific reference. ISBN and page number.

Offhand you could google "Lineweaver expanding confusion"
or google "Lineweaver inflation cosmic microwave background".

You will get some links that say "arxiv". this is a free archive of scientific articles. Lineweaver is a top cosmologist and a good writer. He explains things clearly. I think
Figure 1 in either of those papers would show the particle horizon to be around 46 billion LY.
this is how far away TODAY the most distant matter is that we could in principle be getting a signal from.
this is normally what people mean by the radius of the observable region.

Of course that matter was much closer when it emitted the light, and the light has had to contend with expansion so it has taken some 13 billion years to get to us. But the matter which emitted the light is NOW about 46 billion LY away, because of expansion.

So that is the present distance of the most distant stuff we can see, and it is the radius of the observable. the figures here are estimates. Something around 46, maybe 47, as was said earlier. Can't be too exact.

I have figure 1 from one of Lineweaver's articles in my signature. You could check the figure without even having to go fetch the article from arxiv. If you want.

You can see where the lightcone touches down, around 46 Gly (billion ly). You can see in the figure how it touches down a little over halfway between the 40 Gly mark and the tick for 50 Gly. So it is roughly 46. Also this is where the particle horizon line crosses the level marking present time.

Googling you get the arxiv copies of both articles and both have the same figure 1 in them. It is basic.

 

[Thermate]

OK. I see cosmology has finally caught up with what I was saying decades ago. You are talking about the Universe as treated as simultaneous with the local center of mass of the observable universe. Congratulations to the scientific community! You finally caught up with a high school dropout. As I said, this is a "lensing" effect. One plane of simultaneity is the time that all observers will agree upon when they look at their watches and measure their own time lines relative to the big bang.

But you really CAN'T see that far, because you only see the past for that timeline that is 47 billion light years away. So it is NOT observable.

 

[Drakkith]

But you really CAN'T see that far, because you only see the past for that timeline that is 47 billion light years away. So it is NOT observable.

What isn't observable?

 

[marcus]

But you really CAN'T see that far, because you only see the past for that timeline that is 47 billion light years away. So it is NOT observable.

You see we are just quibbling about words. We see distant matter as it WAS, not as it is today. But we nevertheless OBSERVE that matter TODAY. So it consitutes what we call the observable portion of the universe. that is how cosmologists use the word. You seem to want them to speak differently. 46 Gly is the distance today of matter we are observing today (as it was along time ago)

They have a different word for the present day distance to the farthest galaxy that we will eventually see as it is TODAY. That distance is called the CEH (cosmic event horizon). It is about 16 billion ly. 16 Gly is the distance today of matter which we WILL in our far distant future be able to observe (as that matter is today.)

This is also shown in figure 1.

 

[Thermate]

You see we are just quibbling about words. We see distant matter as it WAS, not as it is today. But we nevertheless OBSERVE that matter. So it consitutes what we call the observable portion of the universe. that is how cosmologists use the word. You seem to want them to speak differently.

They have a different word for the present day distance to the farthest galaxy that we will eventually see as it is TODAY. That distance is called the CEH (cosmic event horizon). It is about 16 billion ly.

This is also shown in figure 1.

Do observables cross the CEH at less than light speed? Wheeler told me that I needed to tell my teacher David Layzer that he should revisit his calculations. IIRC, Wheeler was wrong.

 

[Thermate]

What isn't observable?

The universe 47 billion light years away according to the center of mass plane of natural simultaneity. IOW wristwatch time since the big bang.

 

[Drakkith]

The universe 47 billion light years away according to the center of mass plane of natural simultaneity. IOW wristwatch time since the big bang.

Well, nothing is. Everything is observed as it was in the past.

 

[soothsayer]

You observe your keyboard as it was in the past...

Really? Has the global curvature of the universe changed in the past 13 billion years?

No, it hasn't, not so far as we can tell. Ω = 1 which means Ω has always equaled one, unless maybe you believe inflation.

The distance to the edge of your observable universe is 47 billion years, the universe is 13.7 billion years old. This is not a paradox: space has expanded. Objects at the edge of our observable universe are moving faster than light. That is ok, because no information is actually traveling faster than light.

Considering the "observable universe", no matter how big it is, is a perfect sphere around you, based on the distance you can see in all directions due to the finite speed of light, then the observable universe is always centered on you, and every point in the universe has a different observable universe. The ENTIRE universe is infinite, and has always been infinite, even at the big bang. Imagine you had an infinite plane expanding arbitrarily quickly for points separated by an arbitrarily large distance. What is the center of mass of this unverse? There is none, and never was.

 

[soothsayer]

Do observables cross the CEH at less than light speed?

Essentially, yes. What it's really saying is that this is the boundary at which space is expanding faster than light, such that light emitted from objects RIGHT NOW at this boundary will never reach us, just as light emitted inside a black hole event horizon will never reach us. Anything outside of this CEH (ones that we will eventually see as they are today) are necessarily moving slower than light. I think this horizon is about 12 billion light years away, if I'm not mistaken?

 

[Chronos]

Please provide a specific reference. ISBN and page number.

"Today the diameter of the observable universe is estimated at about 28 billion parsecs (93 billion light-years). This diameter is increasing by 1.96 million km/s, which is about 6.5 times faster than the speed of light in empty space." Extra Dimensions in Space and Time, Bars & Teming, ISBN 978-0-387-77637-8, p27

 

[phinds]

Please provide a specific reference. ISBN and page number.

There is this really nifty thing on the internet called "Google Search". You should learn how to use it.

Try this

http://en.wikipedia.org/wiki/Observable_universe

Which includes the following:

The age of the universe is about 13.75 billion years, but due to the expansion of space humans are observing objects that were originally much closer but are now considerably farther away (as defined in terms of cosmological proper distance, which is equal to the comoving distance at the present time) than a static 13.75 billion light-years distance.[2] The diameter of the observable universe is estimated at about 28 billion parsecs (93 billion light-years),[3] putting the edge of the observable universe at about 46–47 billion light-years away.[4][5]


OOPS ... I see that I missed an entire page of responses on this thread, so this really wasn't necessary.

 

[Thermate]

You observe your keyboard as it was in the past...



No, it hasn't, not so far as we can tell. Ω = 1 which means Ω has always equaled one, unless maybe you believe inflation.

The distance to the edge of your observable universe is 47 billion years, the universe is 13.7 billion years old. This is not a paradox: space has expanded. Objects at the edge of our observable universe are moving faster than light. That is ok, because no information is actually traveling faster than light.

Considering the "observable universe", no matter how big it is, is a perfect sphere around you, based on the distance you can see in all directions due to the finite speed of light, then the observable universe is always centered on you, and every point in the universe has a different observable universe. The ENTIRE universe is infinite, and has always been infinite, even at the big bang. Imagine you had an infinite plane expanding arbitrarily quickly for points separated by an arbitrarily large distance. What is the center of mass of this unverse? There is none, and never was.

It's been well over a decade since I seriously thought about cosmology, so I'm a bit rusty. Something, however, seems wrong with the idea that the curvature is effectively zero.

I'm not saying you are wrong. But consider this. If we draw geodesics on a Euclidean plane, parallels remain at a constant mutual distance. Now the world lines^* of the local universal rest frames are geodesics which are growing further apart in an expanding universe. If space-time were "flat" I would expect geodesics to remain at constant mutual distance.

*I mistakenly used the term "time lines" in a previous post.

 

[Thermate]

"Today the diameter of the observable universe is estimated at about 28 billion parsecs (93 billion light-years). This diameter is increasing by 1.96 million km/s, which is about 6.5 times faster than the speed of light in empty space." Extra Dimensions in Space and Time, Bars & Teming, ISBN 978-0-387-77637-8, p27

I guess this really begs the meaning of "observable". To my way of thinking something that is observable is something that I can observe, IOW "see". What is being called "observable" in the above is really conjecture. It may be reasonable conjecture, but it is a poor choice of wording to call objects which were not 47 billion light years away when they emitted what we can currently observe as "observable" at 47 billion light years.

 

[marcus]

Essentially, yes. What it's really saying is that this is the boundary at which space is expanding faster than light, such that light emitted from objects RIGHT NOW at this boundary will never reach us, just as light emitted inside a black hole event horizon will never reach us. Anything outside of this CEH (ones that we will eventually see as they are today) are necessarily moving slower than light. I think this horizon is about 12 billion light years away, if I'm not mistaken?

If a galaxy is NOW at distance 14 Gly, then the distance to it is now increasing at rate c.
It is a common misconception that this means that light emitted today by anything farther than that will never reach us.

Lineweaver and Davis explained in a SciAm article ("charley" link in my sig) how light can reach us even if emitted from a galaxy the distance to which is increasing somewhat faster than c. It's just a minor point but might interest you.

The distance which is currently increasing at exactly c is called the Hubble radius, commonly estimated to be about 14 Gly.

The Hubble radius is smaller than the CEH, commonly estimated at about 16 Gly. You might be interested in a cosmology calculator (constructed by a PF member, Jorrie) which is online here"
http://www.einsteins-theory-of-relativity-4engineers.com/CosmoLean_A25.html

The row of the table labeled S=1 is the present. The precise numbers depend on what parameter values, like present Hubble expansion rate, you plug in and they are measured only to some finite accuracy, so in conversation one rounds off and says "about". The calculator does not round off for you. It uses recent values of the model parameters.

It says the Hubble radius (distance which is expanding at c) is 13.9 Gly or about 14 Gly.
It says the CEH is currently about 15.9 or 16 Gly.

 

[Drakkith]

I guess this really begs the meaning of "observable". To my way of thinking something that is observable is something that I can observe, IOW "see". What is being called "observable" in the above is really conjecture. It may be reasonable conjecture, but it is a poor choice of wording to call objects which were not 47 billion light years away when they emitted what we can currently observe as "observable" at 47 billion light years.

What makes this different than everything else you see? If a car is moving past you it is actually very slightly further along its path than you see it due to the finite speed of light. The only difference I see is the magnitude of the difference.

 

[phinds]

What makes this different than everything else you see? If a car is moving past you it is actually very slightly further along its path than you see it due to the finite speed of light. The only difference I see is the magnitude of the difference.

I see you keep on doing the same old thing ... being reasonable to people who don't want to be reasonable. Don't you ever get tired of it?

 

[Thermate]

What makes this different than everything else you see? If a car is moving past you it is actually very slightly further along its path than you see it due to the finite speed of light. The only difference I see is the magnitude of the difference.

I agree with that. The reason that it becomes significant in terms of such huge time and distance scales is because the current state of that part of the universe has no effect on our part, and will not for billions of years. Only events billions of years in the past have any bearing on our current state.

 

[phinds]

Only events billions of years in the past have any bearing on our current state.

Now there's a point of view you don't see very often.

 

[Chronos]

Distance is a very messy thing in cosmology. Figuring out where things are at in the universe relative to one another can be very confusing. For example, the most distant observable thing in the universe is the CMB at z~1100. When those photons were emitted, the source of the CMB was a mere 42 million light years from our current position in the universe. At the same time, photons from a galaxy at z~3 were 5.7 BILLION light years distant when emitted by that galaxy. At seems rather illogical that a foreground galaxy at z~3 can emit photons at better than 10 times the distance of the background CMB, but, that is the way it is with expansion. It also provides us with seemingly exotic concepts like luminosity distance and angular diameter distance. If all this does not confuse you, I've done a poor job explaining it.

 

[soothsayer]

It's been well over a decade since I seriously thought about cosmology, so I'm a bit rusty. Something, however, seems wrong with the idea that the curvature is effectively zero.

I'm not saying you are wrong. But consider this. If we draw geodesics on a Euclidean plane, parallels remain at a constant mutual distance. Now the world lines^* of the local universal rest frames are geodesics which are growing further apart in an expanding universe. If space-time were "flat" I would expect geodesics to remain at constant mutual distance.

*I mistakenly used the term "time lines" in a previous post.

The lines separate but remain forever non-intersecting, which means the geometry is always Euclidean. If you take a plane and expand it, the geometry is still Euclidean, even during the expansion. The metric for describing spacetime intervals does not change. This is because the expansion is not due to an "open" cosmic geometry, but due to dark energy. If the universe were open, Ω < 1, or closed, Ω > 1, then the value for Ω would actually change over time, thus the geometry would change over time, but Ω = 1 is constant in time.

 

[Thermate]

The lines separate but remain forever non-intersecting, which means the geometry is always Euclidean.

There are non-Euclidean geometries in which parallel geodesics don't intersect.

 

[soothsayer]

There are non-Euclidean geometries in which parallel geodesics don't intersect.

Here is the deal with these geometries and parallel lines.

Ω > 1, Closed => Elliptical space: parallel lines intersect, the value of Ω changes, but is always > 1. Space contracts, leading to "Big Crunch"

Ω = 1, Flat => Euclidean space: Parellel lines do not intersect, and parallel lines only come in unique pairs. Geometry does not change. Space expands, but decelerates, so that space is constant after an infinite amount of time.

Ω < 1, Open => Hyperbolic space: Parallel lines do not intersect, but to contrast with Euclidean geometry, there are infinitely many unique, parallel, non intersecting lines. I believe all parallel lines diverge. Geometry changes, space expands at an increasing rate forever.

We live in Ω = 1 with Dark Energy. The difference between this and an Ω<1 universe is that there are not infinitely many unique parallel lines ones can draw in a moment in time, even with expansion due to D.E.

 

[soothsayer]

By "unique" parallel lines, I mean this: In Euclidean geometry, we can draw many lines that are parallel to one another, but they are simply translations of one another, which doesn't mean much. If we took a eucliden geodesic and rotated it by ANY angle theta, it will intersect once, at some point. In Hyperbolic geometry, if we have two geodesics of some finite separation, we can rotate one of those geodesics by some finite angle theta such that the lines STILL do not even intersect. In fact, there are infinitely many such lines, as you can easily see, which are all UNIQUE lines. This is the difference between flat space with dark energy and open space--both have expanding geodesics through time, but geodesics also diverge in slices of constant time in a hyperbolic universe.

Inflation complicates the picture. In the typical description of inflation, the universe started as a point, of Ω > 1, and as it expanded, instead of quickly reaching a maximum and re-collapsing, it reached a point where Dark Energy was 27 orders of magnitude stronger than it is today, and rapidly pushed the universe to be flat, that is, Ω is so close to one, we don't notice any difference, and after that very early inflationary period, the geometry of space has not changed any measurable amount. I don't know what effect this would have on the horizon of the observable universe.

 

[TheTechNoir]

I respond frequently to questions that are covered in the FAQ. Any way I apologize I derailed the thread here. And there is a sub-forum for your new ideas that might change the world.

 

[russ_watters]

Starting off in a new forum by criticizing the way they do things is not a good way to start, but there is a bigger problem here:

I Hate it when people use the term " we know" or "the fact that" when citing theories, as long as they are still theories, we don't know anything ( sorta)

This post reflects a severe misunderstanding of how science works. You say "still theories" as if there is something better an idea could be in science. There isn't. Theories are as good as ideas get and when something is solid enough to be a theory it means we do know an awful lot about it.

 

[russ_watters]

Also not to worry, you didn't sound hostile at all.

This is true. Biting off more than you can chew, yes. Hostile/aggressive, no.