# Physics Question

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> Differential manifolds that could be embedded in a higher dimensional space can also exist by and of themselves.

There are no "higher dimensions" in physical space that we can speak of with certainty. We only know that there are the three dimensions our senses give us evidence of. Nor is there such a thing as 'curved space-time' that Dragonfly posted about on another thread.

Dead wrong. Without the space-time manifold we would have no explanation for gravity. The Newtonian force at a distance hypothesis has been falsified for over 150 years. Spacetime is curved by the presence of mass and energy. Gravitation is essentially curvature of the space-time manifold.

The only things that can be curved--acted upon--by mass and energy are mass and energy. Time is a measurement of motion and space of distance and they are only concepts referencing mass and energy which is the only physical stuff of existence. Spacetime is an explanation of something else--not itself. It cannot be curved or bent.

--Brant

Brant,

That's not true. One of the tests of Einstein's theory of general relativity was to check the gravitational lensing of light. The angle of deflection of light is twice what you would expect from a curving of the motion of light with a given energy around a massive object. The remaining effect is due to the curvature of the spacetime manifold.

Jim

Edited by James Heaps-Nelson

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> Differential manifolds that could be embedded in a higher dimensional space can also exist by and of themselves.

There are no "higher dimensions" in physical space that we can speak of with certainty. We only know that there are the three dimensions our senses give us evidence of. Nor is there such a thing as 'curved space-time' that Dragonfly posted about on another thread.

Dead wrong. Without the space-time manifold we would have no explanation for gravity. The Newtonian force at a distance hypothesis has been falsified for over 150 years. Spacetime is curved by the presence of mass and energy. Gravitation is essentially curvature of the space-time manifold.

The only things that can be curved--acted upon--by mass and energy are mass and energy. Time is a measurement of motion and space of distance and they are only concepts referencing mass and energy which is the only physical stuff of existence. Spacetime is an explanation of something else--not itself. It cannot be curved or bent.

--Brant

Brant,

That's not true. One of the tests of Einstein's theory of general relativity was to check the gravitational lensing of light. The angle of deflection of light is twice what you would expect from a curving of the motion of light with a given energy around a massive object. The remaining effect is due to the curvature of the spacetime manifold.

Jim

It seems that all this "spacetime manifold" is, Jim, is an explanation holding place for a better one to come.

--Brant

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> Differential manifolds that could be embedded in a higher dimensional space can also exist by and of themselves.

There are no "higher dimensions" in physical space that we can speak of with certainty. We only know that there are the three dimensions our senses give us evidence of. Nor is there such a thing as 'curved space-time' that Dragonfly posted about on another thread.

Dead wrong. Without the space-time manifold we would have no explanation for gravity. The Newtonian force at a distance hypothesis has been falsified for over 150 years. Spacetime is curved by the presence of mass and energy. Gravitation is essentially curvature of the space-time manifold.

The only things that can be curved--acted upon--by mass and energy are mass and energy. Time is a measurement of motion and space of distance and they are only concepts referencing mass and energy which is the only physical stuff of existence. Spacetime is an explanation of something else--not itself. It cannot be curved or bent.

--Brant

Brant,

That's not true. One of the tests of Einstein's theory of general relativity was to check the gravitational lensing of light. The angle of deflection of light is twice what you would expect from a curving of the motion of light with a given energy around a massive object. The remaining effect is due to the curvature of the spacetime manifold.

Jim

It seems that all this "spacetime manifold" is, Jim, is an explanation holding place for a better one to come.

--Brant

No, it is a description of how spatial dimensions and time are related at different velocities and under different mass and energy densities. In gravity, unlike the other forces we have not yet detected a force carrying particle, we do not yet have a good theory of quantum gravity. Newton's theory was no more exact in this regard. There was no physical mechanism for action at a distance.

Jim

Edited by James Heaps-Nelson

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Jim, aren't scientists looking for gravity waves?

--Brant

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Jim, aren't scientists looking for gravity waves?

--Brant

Still looking. Not yet found.

Ba'al Chatzaf

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Edited by James Heaps-Nelson

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Jim, aren't scientists looking for gravity waves?

--Brant

Still looking. Not yet found.

No direct evidence with measurements on Earth, but there is very strong astronomical evidence. The binary system PSR B1913+16, consisting of a pulsar and a neutron star orbiting each other, shows an orbital decay that is exactly conform the predictions of orbital decay due to the loss of energy by emitting gravitational waves, as predicted by the general theory of relativity. Here is a graph of the observed decay (red dots) and the decay predicted by general relativity (blue line).

Curved space-time at work for you! But of course there are philosophers who "know" that space-time cannot be curved, although they wouldn't know the difference between a Riemann tensor, a Ricci tensor or a Christoffel symbol, but they've decided from their armchairs that this is all nonsense and no doubt they have a theory that can predict that orbital decay much better than such a rationalistic theory as general relativity.

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Yes, I remember the e-mail exchanges, and I wondered if those were "the seed" of your suggestion.

A problem I'm having visualizing is a continuation of the same problem I was having then, which is, that I don't think the appearance of the animations captures what I understand is supposedly proposed in big bang theory. As I understand the supposed "image," from the perspective of any galaxy in the universe, that galaxy would be experienced as itself the "center" of the expansion with basically the same "distribution" being seen as extending in all directions around with quasars and the CMBR appearing as if around a circumference of a surrounding circle. (DF and Ba'al, please comment, if this is your understanding of how the situation is conceived of.)

However, with your animations, what I get in both cases is the image of a center of reference which isn't the vantage point of a particular galaxy but instead is the center of a large spherical shape either from the center of which the galaxies are expanding or by reference to which the perimeters are shrinking. Thus I don't see that from the perspective of any particular galaxy, the distribution seen would be basically the same as from that of any other particular galaxy.

Right. In my animations above, the viewer is outside of the system.

I have this same difficulty with the visualization examples Larry uses. I think the one I described in our exchange several years back was the one of dots on the surface of a balloon being blown up.

I thought that Larry's visualization involved coins glued to a balloon which expands.

Here's what that would look like from outside the system:

And here's what it would look like from the vantage point of any one of the coins (since the balloon is a sphere, you'd have to look through the balloon to see the other coins, and that's what I'm showing here):

As I've said, when viewed from within the system, the coins (galaxies) appear to maintain their position and shrink in size. (And in this animation, they are actually maintaining their size and moving away from the viewer rather than shrinking in size and maintaining their distance from the viewer).

Another he uses is raisins in a bread loaf being baked -- as the dough expands, the distance between raisins increases. But in each case, the "picture" wouldn't be the same from the vantage point of any particular dot or raisin. For example, a raisin near the center of the bread loaf would see raisins all around, but a raisin at the edge wouldn't. There would be a direction -- toward the edge of the loaf -- where there weren't raisins to be seen.

In our earlier discussion, we had addressed the difference between the universe having a dimensional center but its not having an expansional center. My opinion is that a viewer at the edge of the universe wouldn't see anything beyond the edge, just as a raisin at the edge of a loaf wouldn't see raisins all around. But that wouldn't matter. Although someone living at the edge of the universe would be able to recognize that his location was not the dimensional center of the universe, he'd still see his location as appearing to be the expansional center -- his view would be like that from any other point in space in that he would perceive everything else as moving away from him, with farther galaxies moving away proportionally faster than closer ones.

J

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> there are philosophers who "know" that space-time cannot be curved, although they wouldn't know the [mathematics]

That's because while a philosopher may not know the details of some sciences, he can point out that words are not being used in their proper senses. Words have an exact meaning. If saying space is 'curved' is a metaphor, the physicist should not use those terms, but use -exact- terms.

If you get your concepts garbled, all the differential geometry in the world ain't gonna help you.

> they've decided from their armchairs that this is all nonsense.

Brant made a number of good points about what words like "space", "time", and "curvature" mean in post #25. You don't need a degree in physics to tell if the language is being misused. Listen carefully: Curvature only happens in space.

Write that on the blackboard several times, Baal, or turn in your copies of Aristotle's Categories and Metaphysics.

Edited by Philip Coates

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Hey, DF! What kind of chair did Einstein use--or was he standing up? (This is a philosophical discussion board so most discussions of physics will be through philosophical lenses and that is sanctioned by your being here on this thread. Thank you for that.)

--Brant

a boy's just gotta have fun!

Edited by Brant Gaede

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> there are philosophers who "know" that space-time cannot be curved, although they wouldn't know the [mathematics]

That's because while a philosopher may not know the details of some sciences, he can point out that words are not being used in their proper senses. Words have an exact meaning. If saying space is 'curved' is a metaphor, the physicist should not use those terms, but use -exact- terms.

If you get your concepts garbled, all the differential geometry in the world ain't gonna help you.

> they've decided from their armchairs that this is all nonsense.

Brant made a number of good points about what words like "space", "time", and "curvature" mean in post #25. You don't need a degree in physics to tell if the language is being misused. Listen carefully: Curvature only happens in space.

Write that on the blackboard several times, Baal, or turn in your copies of Aristotle's Categories and Metaphysics.

Phil,

When the physicist uses the word curvature in the context of a four dimensional Riemannian space he means: not locally isometric to a Euclidian space. This means the spatial and time dimensions don't stay uniformly orthogonal to each other. How is that different from a curve in two dimensions or three dimensions?

Jim

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> there are philosophers who "know" that space-time cannot be curved, although they wouldn't know the [mathematics]

That's because while a philosopher may not know the details of some sciences, he can point out that words are not being used in their proper senses. Words have an exact meaning. If saying space is 'curved' is a metaphor, the physicist should not use those terms, but use -exact- terms.

If you get your concepts garbled, all the differential geometry in the world ain't gonna help you.

> they've decided from their armchairs that this is all nonsense.

Brant made a number of good points about what words like "space", "time", and "curvature" mean in post #25. You don't need a degree in physics to tell if the language is being misused. Listen carefully: Curvature only happens in space.

Write that on the blackboard several times, Baal, or turn in your copies of Aristotle's Categories and Metaphysics.

Phil,

When the physicist uses the word curvature in the context of a four dimensional Riemannian space he means: not locally isometric to a Euclidian space. This means the spatial and time dimensions don't stay uniformly orthogonal to each other. How is that different from a curve in two dimensions or three dimensions?

Jim

BTW, we use noneuclidean geometry all the time in cartography: the surface of the Earth is curved.

Jim

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> there are philosophers who "know" that space-time cannot be curved, although they wouldn't know the [mathematics]

That's because while a philosopher may not know the details of some sciences, he can point out that words are not being used in their proper senses. Words have an exact meaning. If saying space is 'curved' is a metaphor, the physicist should not use those terms, but use -exact- terms.

If you get your concepts garbled, all the differential geometry in the world ain't gonna help you.

> they've decided from their armchairs that this is all nonsense.

Brant made a number of good points about what words like "space", "time", and "curvature" mean in post #25. You don't need a degree in physics to tell if the language is being misused. Listen carefully: Curvature only happens in space.

Write that on the blackboard several times, Baal, or turn in your copies of Aristotle's Categories and Metaphysics.

The curvature tensors (there are several including the Riemann, the Ricci, the Weyl tensor...) are defined on n-dimensional differentiable manifolds. Curvature can be defined for curves, three dimensional surface, four dimensional manifolds (including the 4-d space-time manifold of physics).

You are a veritable fount of misinformation. Maybe you should learn a thing or two before making pronouncements.

Ba'al Chatzaf

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> Maybe you should learn a thing or two before making pronouncements.

Back at you, pal: I do tutoring but my rates are high.

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Baal, or turn in your copies of Aristotle's Categories and Metaphysics.

I burned mine. Aristotle got just about everything concerning matter and motion wrong.

Dumping Aristotle was like getting rid of my old, no longer used buggy whip. I traded in Aristotle for Boole.

Ba'al Chatzaf

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> there are philosophers who "know" that space-time cannot be curved, although they wouldn't know the [mathematics]

That's because while a philosopher may not know the details of some sciences, he can point out that words are not being used in their proper senses. Words have an exact meaning. If saying space is 'curved' is a metaphor, the physicist should not use those terms, but use -exact- terms.

If you get your concepts garbled, all the differential geometry in the world ain't gonna help you.

> they've decided from their armchairs that this is all nonsense.

Brant made a number of good points about what words like "space", "time", and "curvature" mean in post #25. You don't need a degree in physics to tell if the language is being misused. Listen carefully: Curvature only happens in space.

Write that on the blackboard several times, Baal, or turn in your copies of Aristotle's Categories and Metaphysics.

The curvature tensors (there are several including the Riemann, the Ricci, the Weyl tensor...) are defined on n-dimensional differentiable manifolds. Curvature can be defined for curves, three dimensional surface, four dimensional manifolds (including the 4-d space-time manifold of physics).

You are a veritable fount of misinformation. Maybe you should learn a thing or two before making pronouncements.

Ba'al Chatzaf

Are these "manifolds" artificial mathematical constructs or such constructs only?

--Brant

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> there are philosophers who "know" that space-time cannot be curved, although they wouldn't know the [mathematics]

That's because while a philosopher may not know the details of some sciences, he can point out that words are not being used in their proper senses. Words have an exact meaning. If saying space is 'curved' is a metaphor, the physicist should not use those terms, but use -exact- terms.

If you get your concepts garbled, all the differential geometry in the world ain't gonna help you.

> they've decided from their armchairs that this is all nonsense.

Brant made a number of good points about what words like "space", "time", and "curvature" mean in post #25. You don't need a degree in physics to tell if the language is being misused. Listen carefully: Curvature only happens in space.

Write that on the blackboard several times, Baal, or turn in your copies of Aristotle's Categories and Metaphysics.

The curvature tensors (there are several including the Riemann, the Ricci, the Weyl tensor...) are defined on n-dimensional differentiable manifolds. Curvature can be defined for curves, three dimensional surface, four dimensional manifolds (including the 4-d space-time manifold of physics).

You are a veritable fount of misinformation. Maybe you should learn a thing or two before making pronouncements.

Ba'al Chatzaf

Are these "manifolds" artificial mathematical constructs or such constructs only?

--Brant

They are mathematical objects which underlie physical theories that make correct predictions. They are as real (or unreal) as gravitational fields and electromagnetic fields. Physics is a way to make abstract entities correlate with real observations.

Ba'al Chatzaf

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> there are philosophers who "know" that space-time cannot be curved, although they wouldn't know the [mathematics]

That's because while a philosopher may not know the details of some sciences, he can point out that words are not being used in their proper senses. Words have an exact meaning. If saying space is 'curved' is a metaphor, the physicist should not use those terms, but use -exact- terms.

If you get your concepts garbled, all the differential geometry in the world ain't gonna help you.

> they've decided from their armchairs that this is all nonsense.

Brant made a number of good points about what words like "space", "time", and "curvature" mean in post #25. You don't need a degree in physics to tell if the language is being misused. Listen carefully: Curvature only happens in space.

Write that on the blackboard several times, Baal, or turn in your copies of Aristotle's Categories and Metaphysics.

The curvature tensors (there are several including the Riemann, the Ricci, the Weyl tensor...) are defined on n-dimensional differentiable manifolds. Curvature can be defined for curves, three dimensional surface, four dimensional manifolds (including the 4-d space-time manifold of physics).

You are a veritable fount of misinformation. Maybe you should learn a thing or two before making pronouncements.

Ba'al Chatzaf

Are these "manifolds" artificial mathematical constructs or such constructs only?

--Brant

They are mathematical objects which underlie physical theories that make correct predictions. They are as real (or unreal) as gravitational fields and electromagnetic fields. Physics is a way to make abstract entities correlate with real observations.

Ba'al Chatzaf

Then they are reality bridges that cross ignorance to tentatively acceptable results.

--Brant

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Then they are reality bridges that cross ignorance to tentatively acceptable results.

--Brant

That is a pretty good summary.

Ba'al Chatzaf

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[W]ith your animations, what I get in both cases is the image of a center of reference which isn't the vantage point of a particular galaxy but instead is the center of a large spherical shape either from the center of which the galaxies are expanding or by reference to which the perimeters are shrinking. Thus I don't see that from the perspective of any particular galaxy, the distribution seen would be basically the same as from that of any other particular galaxy.

Right. In my animations above, the viewer is outside of the system.

But the viewer isn't outside of the universe. The point of Larry's visualizations (he isn't the only one who uses those same visualizations; I think they're fairly standard in trying to convey the idea) is to give a visual intuitive sense of what's experienced by the observer within the system looking from a particular galaxy.

I have this same difficulty with the visualization examples Larry uses. I think the one I described in our exchange several years back was the one of dots on the surface of a balloon being blown up.

I thought that Larry's visualization involved coins glued to a balloon which expands.

I think you're right, I did say coins. (The emails are on storage disks from my old laptop and haven't ever been transferred to my current desktop external storage. I'm just going by memory. I don't want to muck around right now trying to find stuff on those old disks.) I think the dots came in from a different illustrative example L and I were messing around with not long ago.

Here's what that would look like from outside the system:

But: halt. No "outside the system." With the universe, there isn't any outside the system, and, repeating, the idea is to convey some sense of what's experienced from within the system.

In the case of the balloon example, the surface film of the balloon is to be thought of as everything there is. Consider it in isolation, abstracting away the air inside and outside the balloon. There's just that surface expanding, nothing else, nothing inside the film of the surface, nothing outside it.

I need to correct something I said about visualizing with the balloon example. I find it less troublesome than the raisins-in-a-loaf image. Suppose you have coins of equal size, and evenly distributed on the film of the balloon, then as the balloon expands, you *can* take any particular coin as the reference center and get the same view of what's happening with the rest of the coins as you'd get taking any other particular coin as the reference center. (You have to ignore the aperture where air is being blown into the balloon, but ignoring that, it's the same view from the vantage point of any coin.) The problem extrapolating to imagining the purported expansion of the universe is that the balloon is just a thin film with the expansion being that only of the film, whereas what one supposedly sees with the universe expanding is everything going away all around as if one were at the center of an expanding sphere.

And here's what it would look like from the vantage point of any one of the coins (since the balloon is a sphere, you'd have to look through the balloon to see the other coins, and that's what I'm showing here):

No looking through the sphere. Only around it.

In our earlier discussion, we had addressed the difference between the universe having a dimensional center but its not having an expansional center.

I'm not recalling that, unless you mean your example of an infinite ruler. (But then no actual ruler is infinite.)

My opinion is that a viewer at the edge of the universe wouldn't see anything beyond the edge, just as a raisin at the edge of a loaf wouldn't see raisins all around. But that wouldn't matter. Although someone living at the edge of the universe would be able to recognize that his location was not the dimensional center of the universe, he'd still see his location as appearing to be the expansional center -- his view would be like that from any other point in space in that he would perceive everything else as moving away from him, with farther galaxies moving away proportionally faster than closer ones.

I don't think that's what's proposed as being seen. Instead that any particular galaxy would experience itself as dimensional center and with basically the same distribution all around as would be experienced from any other galaxy.

Also, aside from visualization issues, you'd need to have some physics reason(s) seriously to propose an alternate theory, and you'd need to be able to address issues which current physics can address. At least ideally you'd need to meet those requirements. Granted, there's an awful lot of just positing models for no good physics reason(s) going on these days, but I don't view this methodology as worthy of emulating.

Ellen

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But the viewer isn't outside of the universe. The point of Larry's visualizations (he isn't the only one who uses those same visualizations; I think they're fairly standard in trying to convey the idea) is to give a visual intuitive sense of what's experienced by the observer within the system looking from a particular galaxy.

I understand. The purpose of my posting the initial clips on this thread was not to illustrate Larry's or anyone else's visualizations from within a proposed model, but to illustrate the issue of alternate perspectives that I've been discussing.

Here's what that would look like from outside the system:

But: halt. No "outside the system." With the universe, there isn't any outside the system, and, repeating, the idea is to convey some sense of what's experienced from within the system.

Again, I understand that, in reality, we can't see the universe from outside the system, and that Larry's visualization is supposed to be from inside the system, which is why the last clip that I posted was from inside the system. I also posted an outside-the-system view to show that my animation model is indeed an expanding system as opposed to a system of contracting individual galaxies as one might think when looking at the final clip. Consider the outside-the-system clips to be supplemental information -- kind of a behind-the-scenes visual aid.

In the case of the balloon example, the surface film of the balloon is to be thought of as everything there is. Consider it in isolation, abstracting away the air inside and outside the balloon. There's just that surface expanding, nothing else, nothing inside the film of the surface, nothing outside it.

Okay, then with those criteria, one would see very little. Because of the curvature of the balloon, you'd see only the edges of the coins that were nearest you, and they'd have to be very close to you. Here's what it would look like:

As I've been saying, the visual effect would be exactly the same as it would if the coins maintained their position and shrank in size, as seen here:

In our earlier discussion, we had addressed the difference between the universe having a dimensional center but its not having an expansional center.

I'm not recalling that, unless you mean your example of an infinite ruler. (But then no actual ruler is infinite.)

Right, we discussed the example of an infinite ruler, but, more importantly, we also discussed a finite one. The relevant effect would be the same with both: If we were standing on either an expanding infinite ruler or one that was, say, 2 by 100 yards, and we and the ruler were the only things that existed, we would not be able to determine an expansional center. Any point that we moved to along the ruler would appear to be its expansional center.

My opinion is that a viewer at the edge of the universe wouldn't see anything beyond the edge, just as a raisin at the edge of a loaf wouldn't see raisins all around. But that wouldn't matter. Although someone living at the edge of the universe would be able to recognize that his location was not the dimensional center of the universe, he'd still see his location as appearing to be the expansional center -- his view would be like that from any other point in space in that he would perceive everything else as moving away from him, with farther galaxies moving away proportionally faster than closer ones.

I don't think that's what's proposed as being seen. Instead that any particular galaxy would experience itself as dimensional center and with basically the same distribution all around as would be experienced from any other galaxy.

I've never heard scientists claiming sameness in distribution, only sameness in proportionality of expansion. I don't think I've ever heard any physicists distinguishing between dimensional and expansional centers when discussing proposed shapes or visualizations of the universe. [Edited to add:] I've always taken them to be talking only about the impossibility of identifying a single expansional center, and not of the impossibility of ever identifying a dimensional center.

Also, aside from visualization issues, you'd need to have some physics reason(s) seriously to propose an alternate theory, and you'd need to be able to address issues which current physics can address.

That's what I've been doing. I've been exploring possibilities and asking questions based on the physics of the simple simulations I've constructed, and I've been doing so while keeping in mind the problems that current physics apparently can't answer. One of the purposes of this thread was to ask if there is a valid reason why we have chosen one unit of measurement as our standard or constant and not another. In other words, if we assume that the distance between the centers of galaxies is constant, rather than expanding, are the consequences inconsistent with our current understanding of the laws of physics?

At least ideally you'd need to meet those requirements. Granted, there's an awful lot of just positing models for no good physics reason(s) going on these days, but I don't view this methodology as worthy of emulating.

I think the only relevant question is can you (or anyone) disprove my proposed alternate model? Can you demonstrate that the laws of physics definitely rule out the idea that the distances between centers of galaxies generally remain constant and that the galaxies are shrinking in size?

J

Edited by Jonathan

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J, I'm answering your post #46 in segments, since trying to read through the whole post at once starts sending my sight swimming.

But the viewer isn't outside of the universe. The point of Larry's visualizations (he isn't the only one who uses those same visualizations; I think they're fairly standard in trying to convey the idea) is to give a visual intuitive sense of what's experienced by the observer within the system looking from a particular galaxy.

I understand. The purpose of my posting the initial clips on this thread was not to illustrate Larry's or anyone else's visualizations from within a proposed model, but to illustrate the issue of alternate perspectives that I've been discussing.

Here's what that would look like from outside the system:

But: halt. No "outside the system." With the universe, there isn't any outside the system, and, repeating, the idea is to convey some sense of what's experienced from within the system.

Again, I understand that, in reality, we can't see the universe from outside the system, and that Larry's visualization is supposed to be from inside the system, which is why the last clip that I posted was from inside the system. I also posted an outside-the-system view to show that my animation model is indeed an expanding system as opposed to a system of contracting individual galaxies as one might think when looking at the final clip. Consider the outside-the-system clips to be supplemental information -- kind of a behind-the-scenes visual aid.

In the case of the balloon example, the surface film of the balloon is to be thought of as everything there is. Consider it in isolation, abstracting away the air inside and outside the balloon. There's just that surface expanding, nothing else, nothing inside the film of the surface, nothing outside it.

Okay, then with those criteria, one would see very little. Because of the curvature of the balloon, you'd see only the edges of the coins that were nearest you, and they'd have to be very close to you. Here's what it would look like:

As I've been saying, the visual effect would be exactly the same as it would if the coins maintained their position and shrank in size, as seen here:

I realize that I misled with these two statements:

[....] The point of [the] visualizations [...] is to give a visual intuitive sense of what's experienced by the observer within the system looking from a particular galaxy.

[...] repeating, the idea is to convey some sense of what's experienced from within the system.

Actually, the point of the visualizations is just to give an initial intuitive sense of what cosmologists are talking about when they say that there was an expansion OF space, what it means for space to expand. A person can easily understand that the balloon expands and so the coins on it get farther apart, likewise that the bread loaf expands and so the raisins get farther apart.

Where visualizing from a particular galaxy's perspective came in was from me -- my attempts to visualize what I've understood the cosmologists to be saying about everything moving away equally from everything else and my attempts to fit this to the heuristics. I can do this more easily with the balloon than with the raisined loaf, since there is the same distribution of coins on the balloon surface from the perspective of any particular coin (ignoring the air aperture). But still, this doesn't convey what I've understood as being described.

Since neither of the visualizations is meant as any sort of accurate model, it isn't useful to push the details in exploring why cosmologists conclude that the universe is expanding.

However, addressing what one would "see" -- IF the balloon were meant as a model -- one would see more than the small area you indicate, since if the film of the balloon were meant as a model of the universe, light would be traveling on paths inside the film, it would be curving and one would see along the curve. It wouldn't be like looking out standing on the surface of the earth, where one's view is bounded by the horizon and one is seeing via incident light waves from a source outside the planet.

(Due to the bending of light, we can see a little ways over the curve of the horizon, but not much. I once saw this startlingly looking out at the Gulf of Mexico with a view where the water was placid and nothing was obstructing. I could plainly see that the horizon was an arc of a circle and that there was a rounding and continuing over the edge.)

Supposing the balloon were a large surface and one was inside one of the coins (which would be embedded in the film, not on top of it, if we're trying for a semblance of accuracy to the universe), I think one wouldn't be able to tell visually if the film was expanding and the other coins being carried farther away or if the other coins were contracting. One might have *other* ways of telling besides visually, but I think there wouldn't be a way to tell just from the appearance.

Ellen

Edited by Ellen Stuttle

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Explanation re expansional center of an expanding ruler noted.

My opinion is that a viewer at the edge of the universe wouldn't see anything beyond the edge, just as a raisin at the edge of a loaf wouldn't see raisins all around. But that wouldn't matter. Although someone living at the edge of the universe would be able to recognize that his location was not the dimensional center of the universe, he'd still see his location as appearing to be the expansional center -- his view would be like that from any other point in space in that he would perceive everything else as moving away from him, with farther galaxies moving away proportionally faster than closer ones.

I don't think that's what's proposed as being seen. Instead that any particular galaxy would experience itself as dimensional center and with basically the same distribution all around as would be experienced from any other galaxy.

I've never heard scientists claiming sameness in distribution, only sameness in proportionality of expansion. I don't think I've ever heard any physicists distinguishing between dimensional and expansional centers when discussing proposed shapes or visualizations of the universe. [Edited to add:] I've always taken them to be talking only about the impossibility of identifying a single expansional center, and not of the impossibility of ever identifying a dimensional center.

I think what's claimed is a basically uniform distribution all around from any vantage point (and realize that what we're seeing in looking out at the universe is backward in time). I'll have to check further to find out if my understanding of the supposed "vista" is correct.

Ellen

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Also, aside from visualization issues, you'd need to have some physics reason(s) seriously to propose an alternate theory, and you'd need to be able to address issues which current physics can address.

That's what I've been doing. I've been exploring possibilities and asking questions based on the physics of the simple simulations I've constructed, and I've been doing so while keeping in mind the problems that current physics apparently can't answer. One of the purposes of this thread was to ask if there is a valid reason why we have chosen one unit of measurement as our standard or constant and not another. In other words, if we assume that the distance between the centers of galaxies is constant, rather than expanding, are the consequences inconsistent with our current understanding of the laws of physics?

I think so. I think you'd have to have general relativity be wrong, but I'm not sure about that. DF (when you resume posting)? Ba'al?

At least ideally you'd need to meet those requirements. Granted, there's an awful lot of just positing models for no good physics reason(s) going on these days, but I don't view this methodology as worthy of emulating.

I think the only relevant question is can you (or anyone) disprove my proposed alternate model? Can you demonstrate that the laws of physics definitely rule out the idea that the distances between centers of galaxies generally remain constant and that the galaxies are shrinking in size?

J

I don't agree that the only relevant question is whether one can disprove a proposed model. Can anyone disprove that the moon orbits the earth because a chain of undetectable gremlins pushes it along an undetectable wire? I think you need some testable predictions.

Ellen

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I think so. I think you'd have to have general relativity be wrong, but I'm not sure about that. DF (when you resume posting)? Ba'al?

Currently Einstein's General Theory of Relativity is the reigning champion theory for gravitation. I have no doubt that conditions in extreme gravitation fields will not be correctly described by the theory, for example the conditions inside of black holes. In fact, it is conceded, that in the near vicinity of a black hole singularity none of the laws of physics are applicable.

I think that our most loved theories will come apart or fray in sufficiently extreme circumstances. It is just a matter of finding these circumstances. If we do we can falsify our best theories.

I do not hold that theories express The Truth. I think they are human intellectual artifacts that describe physical reality to some degree or another. Theories are models, not Revalations of The Truth. The universe is what it is and our theories are our best efforts to understand the universe.

Ba'al Chatzaf

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