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earthman2110
2004-Jan-24, 12:02 AM
Heres another good one for you:
Galaxies travel through space, away from each other, and most galaxies travel at very high speeds. If time slows down to the traveler, or galaxy as it approaches the speed of light, and our galaxy is moving many times faster than another galaxy, would our galaxy be younger, given they were both formed at the same time? Would two people born at the same time, one was born here on earth and one born on a planet in a slower moving galaxy actually be different ages? and how would one determine what the "same time" is here in relation to another galaxy?

rwald
2004-Jan-24, 12:16 AM
That's the problem (well, not real problem, but conceptual problem) with special relativity. If two individuals (let's call them Alice and Bob for simplicity) are traveling away from one another at relativistic speeds, then Alice thinks that Bob's clock is running slowly and that Bob has aged less than her, while Bob thinks the same about Alice. But as you pointed out, they can never actually meet and compare their data. If they want to meet, one or both of them will need to accelerate their ship back in the opposite direction. Because of that acceleration, the two points of view are not equal, and so they'll both agree on who should be older than the other. (If they both accelerate equally back towards the middle, they'll both agree that they should be the same age. So there would be no conflict in that event either.)

Likewise, if we're looking at a galaxy 1 billion light-years away which appears to be just as old as ours, it's really 1 billion years older, because that's how long the light took to get there. Someone in that galaxy would observe our galaxy to be 2 billion light-years younger than their own.

Sam5
2004-Jan-24, 12:42 AM
Heres another good one for you:
Galaxies travel through space, away from each other, and most galaxies travel at very high speeds. If time slows down to the traveler, or galaxy as it approaches the speed of light, and our galaxy is moving many times faster than another galaxy, would our galaxy be younger, given they were both formed at the same time? Would two people born at the same time, one was born here on earth and one born on a planet in a slower moving galaxy actually be different ages? and how would one determine what the "same time" is here in relation to another galaxy?

There is no “time dilation” in galaxies that are moving faster than “c” relative to us. If there was, then their molecular vibration rate would shrink to zero, according to SR theory, and they would be frozen solid. But they aren’t frozen solid, because we can see them glowing.

The “speed limit” and “time dilation” of SR theory was taken from Lorentz theory, and Lorentz based his theory on movement through fields, not just “relative motion”. Just “relative motion” can not slow down any clock or “time” or molecular vibration rate.

Sam5
2004-Jan-24, 12:45 AM
Likewise, if we're looking at a galaxy 1 billion light-years away which appears to be just as old as ours, it's really 1 billion years older, because that's how long the light took to get there. Someone in that galaxy would observe our galaxy to be 2 billion light-years younger than their own.

1 billion years younger than their own. That is classical 1842 Doppler theory.

rwald
2004-Jan-24, 12:49 AM
Well, they would only see our galaxy being born when theirs was 2 billion years old. If they were calculating for distance, they would know that ours was really only 1 billion years younger, not 2, but that's the same as the fact that we "see" them to be the same age, but calculate them to be 1 billion years older.

Now, about your first post. How could a galaxy be moving away from us faster than c? I thought that nothing could move faster than c. I know there are some circumstances under which an object can appear to move faster than c, but I thought those were just illusions set up by odd series of events. Also, I thought that it was relative motion that caused time dialation; if I see you moving at a speed v with respect to me, I think that every one second as measured by your clock is gamma seconds as measured by mine. Where do fields enter into this?

Sam5
2004-Jan-24, 12:54 AM
Well, they would only see our galaxy being born when theirs was 2 billion years old. If they were calculating for distance, they would know that ours was really only 1 billion years younger, not 2, but that's the same as the fact that we "see" them to be the same age, but calculate them to be 1 billion years older.

Ok, I see what you mean.

Sam5
2004-Jan-24, 01:01 AM
Now, about your first post. How could a galaxy be moving away from us faster than c? I thought that nothing could move faster than c. I know there are some circumstances under which an object can appear to move faster than c, but I thought those were just illusions set up by odd series of events. Also, I thought that it was relative motion that caused time dialation; if I see you moving at a speed v with respect to me, I think that every one second as measured by your clock is gamma seconds as measured by mine. Where do fields enter into this?

Well, it’s like this... there is a debate in astronomy about this. Some astronomers say they are NOT moving faster than c relative to us, while some say they ARE moving faster than c relative to us.

I’ve figured out a way they could violate the “c” speed limit.

That speed limit is based on Lorentz’s “motion through fields” idea. So, the speed limit might apply here on earth and inside our galaxy and inside other galaxies, because of all the gravity fields inside galaxies. But, if the most distant galaxies are NOT moving through fields, then there might not be any speed limit at all.

See? Lorentz said it was the fields that put up the resistance to the movement of atoms and masses. That’s why he had atoms and physical things “shrinking” in their direction of motion.

But if the distant galaxies are moving into empty space, free of strong fields, then they might not have a speed limit.

Yes they are moving into the gravity fields of the galaxies that are out ahead of them, but those are the weak parts of the fields, and the fields of the forward galaxies (the ones most further away) might have a “sucking” effect, that pulls on the galaxies behind them.

What started all of this motion, no one knows.

I mean, in terms of physics they don’t know.

rwald
2004-Jan-24, 01:16 AM
Actually, if I recall, Lorentz personally believed that a literal ether existed; it just so happened (according to Lorentz) that the ether would warp space and time using his now-famous equations. So, I'm not sure that the fact that Lorentz originally thought of his equations as applying to "motion through fields" necessarily means much.

Personally, I don't like the idea that distant object could exceed c, even if they're beyond any local gravitational field. If that were true, there could be an observer who were sitting in between the two galaxies who would see neither galaxy moving greater than c (well, if the exact speeds were tweaked properly, etc.). If he sees everyone as moving less than c, then I don't see why the observers in the galaxies should see anything moving faster than c.

Sam5
2004-Jan-24, 01:24 AM
Actually, if I recall, Lorentz personally believed that a literal ether existed; it just so happened (according to Lorentz) that the ether would warp space and time using his now-famous equations. So, I'm not sure that the fact that Lorentz originally thought of his equations as applying to "motion through fields" necessarily means much.

It is quite interesting that his “ether” acted like a “field” and his “fields” acted like an “ether”. That’s why Einstein was able to use his equations.

In Einstein’s 1911 theory, his gravitational fields acted like an “ether”.

Personally, I don't like the idea that distant object could exceed c, even if they're beyond any local gravitational field. If that were true, there could be an observer who were sitting in between the two galaxies who would see neither galaxy moving greater than c (well, if the exact speeds were tweaked properly, etc.). If he sees everyone as moving less than c, then I don't see why the observers in the galaxies should see anything moving faster than c.

The further away they are, the faster they seem to move, relative to any observer.

Newton called this “big bang” theory a “projectile impulse”.

rwald
2004-Jan-24, 01:36 AM
Well, let's say that it appears that some distant galaxy appears to be moving away from us at 1.5c. An observer sitting between the two galaxies would see each receading at some speed less than 1.5c. If this speed is less than c, then when you add together the two velocities, it wouldn't exceed 1c, because of the velocity-sum equations. If the speed is still greater than c, then you could pick another observer between the middle observer and one galaxy, and continue doing so until you get some speed less than c, reducing this down to the first argument. I don't really see how any observer could see another galaxy to be moving away at speeds greater than c.

Sam5
2004-Jan-24, 01:46 AM
Well, let's say....

Well, the estimated speeds are based on their redshifts. Some people think the redshifts are due to distance only, something caused by the Compton Effect.

Look, we’ve got a choice.... either they are all moving apart at rapid speeds, including speeds greater than c, or something is holding them in place, keeping them from collapsing due to all the gravitational pull of all of them. Either way, something unusual is going on, and it’s more than we can understand right now.

This is the same problem that confronted Newton 350 years ago.

Sam5
2004-Jan-24, 01:51 AM
I don't really see how any observer could see another galaxy to be moving away at speeds greater than c.

Here, read this. They tell you how it can happen. The light starts out slow relative to us and it gradually speeds up:

russ_watters
2004-Jan-24, 02:03 AM
Earthman, it isn't really correct to say galaxies are traveling away from each other. The observed motion in the redshift is actually the space between the galaxies expanding. So this isn't a relativity, nor is it a twins paradox issue.

Sam5
2004-Jan-24, 02:11 AM
Earthman, it isn't really correct to say galaxies are traveling away from each other. The observed motion in the redshift is actually the space between the galaxies expanding. So this isn't a relativity, nor is it a twins paradox issue.

“Expanding space” is absurd. Things move. Galaxies move through space. Distance changes.

The idea that the galaxies are “stationary” and the “space between them” expands is a silly superstition. That’s like medieval hocus pocus, magic.

Musashi
2004-Jan-24, 02:16 AM
Thanks for the laugh Sam, honestly.

Sam5
2004-Jan-24, 02:28 AM
Thanks for the laugh Sam, honestly.

Why don’t you tell us what “space” is and how it “expands”. Does it “stretch”, or is “new space” just added to the old space?

Where do we get this “new space”? Who puts it between the distant galaxies?

Oh, and can you link us to a scientific paper that tells us where this “new space” comes from?

Ian Goddard
2004-Jan-24, 02:34 AM
If time slows down to the traveler, or galaxy as it approaches the speed of light, [...]
Keep in mind that time remains constant for any traveler relative to herself. So if I've taken off from the Earth in a rocket and am approaching c, I cannot detect any alteration of my clock. On the other hand, to the folks back on Earth my transmitted voice is becoming increasingly slower. In other words, they detect my clock slowing down... and I detect their clock speeding up.

If I then accelerate back to the Earth I will find once I've returned that I'm younger than my twin. This is call the twin paradox. The key to the aging asymmetry is my nonuniform (or accelerating) motion versus the uniform motion of my twin on Earth (which is accelerating to the extent that circular motion (of the Earth around the Sun) is inherently an acceleration, but for practical purposes of the example is uniform compared to my rocket approaching c). Notice that this is different from the scenario you describe.

Sam5
2004-Jan-24, 02:54 AM
If time slows down to the traveler, or galaxy as it approaches the speed of light, [...]
Keep in mind that time remains constant for any traveler relative to herself. So if I've taken off from the Earth in a rocket and am approaching c, I cannot detect any alteration of my clock.

If you accelerate to near c, I think you would notice some high g forces.

rwald
2004-Jan-24, 03:39 AM
The g forces would only depend on the magnitude of your acceleration. If you accelerated at 32 m/s^2 for years until you were traveling near c, you still would feel just the same as you would on Earth. Of course, if you accelerated to near c very quickly, then the magnitude of the acceleration would be higher, and that would cause you to feel high g forces.

Ian Goddard
2004-Jan-24, 03:42 AM
If time slows down to the traveler, or galaxy as it approaches the speed of light, [...]
Keep in mind that time remains constant for any traveler relative to herself. So if I've taken off from the Earth in a rocket and am approaching c, I cannot detect any alteration of my clock.

If you accelerate to near c, I think you would notice some high g forces.
Yeah, okay... and nothing I said implied otherwise.

russ_watters
2004-Jan-24, 07:59 AM
Thanks for the laugh Sam, honestly. Oy. Sometimes I wonder why we bother with him, but every now and then we get a gem like that. That makes it worthwhile. :lol:

Sam5
2004-Jan-24, 03:48 PM
russ_watters, Musashi,

Question #1:

Here are two questions for you guys. You say that the galaxies “don’t move” but that “the space in between the galaxies expands”. So, question # 1 is, how does the “space expand”? Does the old space “stretch” or is “new space” added to the “old space”? If so, where does the “new space” come from? Give us some science papers that explain how this works.

Question #2:

Here’s the situation. It’s very simple:

An atomic clock ticks slow in a valley and fast on a mountain.

An atomic clock in a valley will measure “c” as the speed of a horizontal beam of light in a valley.

An atomic clock on a mountain will measure “c” as the speed of a horizontal beam of light on a mountain.

This means the speed of the light beam in a valley is moving slower than the speed of the light beam on the mountain.

This means the speed of light is variable at different places in a gravity field, and this is what Einstein said in his 1911 paper and his 1916 book.

So why is this such a big secret in science today?

Normandy6644
2004-Jan-24, 05:06 PM
russ_watters, Musashi,

Question #1:

Here are two questions for you guys. You say that the galaxies “don’t move” but that “the space in between the galaxies expands”. So, question # 1 is, how does the “space expand”? Does the old space “stretch” or is “new space” added to the “old space”? If so, where does the “new space” come from? Give us some science papers that explain how this works.

This is actually a very good question. I think it's more philosophical in asking what space really "is," but either way we still observe expansion and distance between galaxies, so there must be something there.

Question #2:

Here’s the situation. It’s very simple:

An atomic clock ticks slow in a valley and fast on a mountain.

An atomic clock in a valley will measure “c” as the speed of a horizontal beam of light in a valley.

An atomic clock on a mountain will measure “c” as the speed of a horizontal beam of light on a mountain.

This means the speed of the light beam in a valley is moving slower than the speed of the light beam on the mountain.

This means the speed of light is variable at different places in a gravity field, and this is what Einstein said in his 1911 paper and his 1916 book.

So why is this such a big secret in science today?

Sam5
2004-Jan-24, 06:24 PM
russ_watters, Musashi,

Question #1:

Here are two questions for you guys. You say that the galaxies “don’t move” but that “the space in between the galaxies expands”. So, question # 1 is, how does the “space expand”? Does the old space “stretch” or is “new space” added to the “old space”? If so, where does the “new space” come from? Give us some science papers that explain how this works.

This is actually a very good question. I think it's more philosophical in asking what space really "is," but either way we still observe expansion and distance between galaxies, so there must be something there.

Well, thank you very much.

I maintain that the “expansion of space” was just a philosophical term that was pulled out of thin air so as to protect Einstein’s “speed limit of ‘c’” claim in his 1905 paper.

What we actually seem to have is galaxies MOVING THROUGH SPACE at faster than “c”, and if that is the case, that would suggest that Einstein’s 1905 “speed limit” (which was actually Lorentz’s speed limit) was wrong.

So, anyone who claims “space is expanding” should be able to explain exactly “how” space is expanding, in terms of physics, or they should just shut up about it.

If they can’t explain it physically, in terms of physics, then it is nothing more than a belief in either “magic” or “miracles”, with no scientific basis whatsoever.

Sam5
2004-Jan-24, 06:28 PM
This is actually a very good question.

My “belief” is actually a very good scientifically based compromise.

I say the “speed limit” applies to motion of matter through “fields”, but it does not apply to motion of matter in deep space because that motion is not “through fields” but through “empty space”. This is based on Lorentz theory. The reason why Einstein and Lorentz probably didn’t figure this out was because they did not know of any large objects like galaxies that were traveling so fast.

If they were alive today I think they would agree with my point of view, because today they would know about the high redshifts of the distant galaxies. They did not know about such a thing in 1905.

Celestial Mechanic
2004-Jan-25, 05:58 AM
[Snip!]So, anyone who claims “space is expanding” should be able to explain exactly “how” space is expanding, in terms of physics, or they should just shut up about it.

If they can’t explain it physically, in terms of physics, then it is nothing more than a belief in either “magic” or “miracles”, with no scientific basis whatsoever.
The expansion of spacetime was first explained in Einstein's 1917 paper, Cosmological Considerations on the General Theory of Relativity. It makes use of the 1915 paper that you never discuss because the math is so obviously beyond you. The expansion of spacetime is a direct consequence of Einstein's equations.

Suggestion: learn the math, then get Misner, Thorne and Wheeler's Gravitation and read up on cosmology. The book is a little dated because they lean towards a closed and bounded universe. And so it goes...

Sam5
2004-Jan-25, 06:34 AM
The expansion of spacetime was first explained in Einstein's 1917 paper, Cosmological Considerations on the General Theory of Relativity.

His 1917 paper is the one with the cosmological constant in it and curved universal space. He had to withdraw that paper when Hubble discovered the redshifts, and Einstein did that in a paper he wrote with de Sitter in 1932. I’ve got a copy of both papers. Back in 1917 Einstein thought all the distant stars were “fixed” and he doesn’t have an expanding universe or “expanding space” in that paper. When he removed the cosmological constant and the curve space in 1932, the galaxies were free to move through space, which is something he tried to avoid with his 1916 paper.

There is no such thing as “expanding space”.

He said in 1932:

“There is no direct observational evidence for the curvature, the only directly observed data being the mean density and the expansion, which latter proves that the actual universe corresponds to the non-statical case. It is therefore clear that from the direct data of observation we can derive neither the sign nor the value of the curvature, and the question arises whether it is possible to represent the observed facts without introducing a curvature at all.”

“Although, therefore, the density corresponding to the assumption of zero curvature and to the coefficient of expansion may perhaps be on the high side, it certainly is of the correct order of magnitude, and we must conclude that at the present time it is possible to represent the facts without assuming a curvature of three-dimensional space. The curvature is, however, essentially determinable, and an increase in the precision of the data derived from observations will enable us in the future to fix its sign and to determine its value.”

And in the 1932 paper he has the galaxies moving apart by means of motion, with no “expansion of space”. He gives the formula of the motion of the galaxies to be:

h = 500 km./sec. per 10^6 parsecs.

And of course Hubble’s own calculations have the galaxies moving through too.

I’ve got a 1959 University astronomy book that has the galaxies moving through space.

The “expansion of space” idea only started being promoted when the high-z galaxies were discovered in the 1960s-‘90s, and that indicated they were moving faster than “c” relative to the earth. So, in the continuing effort to try to salvage Einstein’s 1905 “speed limit” prediction, all of a sudden we started hearing about “the expansion of space”, with the galaxies “not moving” at all! But nobody can give any scientific explanation of it, because it’s nonsense. It’s one of the greatest con-jobs of modern cosmology.

Diamond
2004-Jan-26, 09:42 AM
Heres another good one for you:
Galaxies travel through space, away from each other, and most galaxies travel at very high speeds. If time slows down to the traveler, or galaxy as it approaches the speed of light, and our galaxy is moving many times faster than another galaxy, would our galaxy be younger, given they were both formed at the same time? Would two people born at the same time, one was born here on earth and one born on a planet in a slower moving galaxy actually be different ages? and how would one determine what the "same time" is here in relation to another galaxy?

There is no “time dilation” in galaxies that are moving faster than “c” relative to us. If there was, then their molecular vibration rate would shrink to zero, according to SR theory, and they would be frozen solid. But they aren’t frozen solid, because we can see them glowing.

The “speed limit” and “time dilation” of SR theory was taken from Lorentz theory, and Lorentz based his theory on movement through fields, not just “relative motion”. Just “relative motion” can not slow down any clock or “time” or molecular vibration rate.

Drivel. [-X

Andreas
2004-Jan-26, 03:41 PM
There is no “time dilation” in galaxies that are moving faster than “c” relative to us. If there was, then their molecular vibration rate would shrink to zero, according to SR theory, and they would be frozen solid. But they aren’t frozen solid, because we can see them glowing.
Um, we wouldn't be able to see a galaxy that recedes at superluminal speed because its light never reaches us. Thus we can't "see them glowing."

And for something different:

If you accelerated at 32 m/s^2 for years until you were traveling near c, you still would feel just the same as you would on Earth.
The numbers are wrong, Earth surface gravity is 9.81 m/s^2 (or 35.30 km/h/s).

milli360
2004-Jan-26, 04:03 PM
And for something different:

If you accelerated at 32 m/s^2 for years until you were traveling near c, you still would feel just the same as you would on Earth.
The numbers are wrong, Earth surface gravity is 9.81 m/s^2 (or 35.30 km/h/s).
I'm sure he meant 32 feet /s^2. :)

Sam5
2004-Jan-26, 04:09 PM
Um, we wouldn't be able to see a galaxy that recedes at superluminal speed because its light never reaches us. Thus we can't "see them glowing."

This was a common belief among some astronomers before Davis and Lineweaver wrote their famous paper three years ago. But they provided an explanation of the physical mechanism of how a photon from a superluminal galaxy can reach us. From their point of view, the light speeds up while on the way to the earth, as it passes through different areas of “comoving space” that are closer to the earth and that are not moving away from the earth as fast as the “comoving space” of the galaxy that emitted the light.

Using the basic 1911 Einstein theory, I say the “comoving space” of galaxies are merely the “local gravitational fields” of the galaxies, and those fields regulate the speed of light locally, at and near those galaxies. Our collective gravitational fields within our galaxy regulate the speed of light inside our galaxy. Our fields are what modern cosmologists tend to call our local “comoving space”. Here is the Davis-Lineweaver paper. This is new, but it is mainstream astronomy and cosmology now:

Sam5
2004-Jan-26, 04:14 PM
Milli, what do you think about what I have said about Einstein changing the reason for the 1905 clock slow-down from “relative motion” to a physical force caused by a “gravitational field” in 1918?

milli360
2004-Jan-26, 04:22 PM
Milli, what do you think about what I have said about Einstein changing the reason for the 1905 clock slow-down from “relative motion” to a physical force caused by a “gravitational field” in 1918?
As near I as I can tell, you have misinterpreted it. It's not "physical force," that is the culprit. As we've discussed, two clocks can experience the same force, but be at different rates, according to GR.

At a certain point, our intuition fails us, and we have to resort to the original formulation of the theory.

Sam5
2004-Jan-26, 05:56 PM
As near I as I can tell, you have misinterpreted it. It's not "physical force," that is the culprit. As we've discussed, two clocks can experience the same force, but be at different rates, according to GR.

Could you point out that claim in any of the original GR theorys? give me the exact wording in the original papers, and then we can discuss it.

milli360
2004-Jan-26, 07:29 PM
Could you point out that claim in any of the original GR theorys? give me the exact wording in the original papers, and then we can discuss it.
I thought you agreed that clocks on the equipotential surface of the Earth were at the same rate, according to GR?

Sam5
2004-Jan-26, 07:43 PM
It's not "physical force," that is the culprit. As we've discussed, two clocks can experience the same force, but be at different rates, according to GR.

Please show us a reference from the original GR theory papers.

milli360
2004-Jan-26, 08:18 PM
Please show us a reference from the original GR theory papers.
I don't have them. My copies are at the library. :)

Do you disagree with that then?

Chip
2004-Jan-27, 08:00 AM
For reference:

Copy of Einstein's 1905 "Theory of Special Relativity" in the original edition and language: "Zur Elektrodynamik bewegter Körper." (Some of the posters here are from Germany - and some other folks read German. Perhaps for reference, it would be nice to have access to the original paper in German from 1905.) (Note that in 1905 "v" stood for the speed of light.)

Here is the 1923 English translation: (Note that "c" is now used for the speed of light by the translator. See also the "Editor's Notes" at the end of the paper which describe corrections of erroneous incorrect translations and errors found in the 1923 translation.)

http://www.fourmilab.ch/etexts/einstein/specrel/www/

Einstein's follow-up paper also from 1905:

http://www.fourmilab.ch/etexts/einstein/E_mc2/www/

russ_watters
2004-Jan-27, 04:42 PM
There is no such thing as “expanding space”.

I’ve got a 1959 University astronomy book that has the galaxies moving through space.

The “expansion of space” idea only started being promoted when the high-z galaxies were discovered in the 1960s-‘90s, and that indicated they were moving faster than “c” relative to the earth. So, in the continuing effort to try to salvage Einstein’s 1905 “speed limit” prediction, all of a sudden we started hearing about “the expansion of space”, with the galaxies “not moving” at all! But nobody can give any scientific explanation of it, because it’s nonsense. It’s one of the greatest con-jobs of modern cosmology. So your view is that galaxies are moving away from each other but space itself is not expanding? Ok - so you're saying that there is a finite number of galaxies and an infinite empty space into which they are moving? Am I understanding your position correctly?

The question then becomes: why can't we see a variation in the density of galaxies (or the CMBR) which shows us where the edge is? Why can't we determine the direction to the center by observing the motion of the galaxies around us?

Data, Sam, does not support your position.

Sam5
2004-Jan-27, 05:19 PM
There is no such thing as “expanding space”.

I’ve got a 1959 University astronomy book that has the galaxies moving through space.

The “expansion of space” idea only started being promoted when the high-z galaxies were discovered in the 1960s-‘90s, and that indicated they were moving faster than “c” relative to the earth. So, in the continuing effort to try to salvage Einstein’s 1905 “speed limit” prediction, all of a sudden we started hearing about “the expansion of space”, with the galaxies “not moving” at all! But nobody can give any scientific explanation of it, because it’s nonsense. It’s one of the greatest con-jobs of modern cosmology. So your view is that galaxies are moving away from each other but space itself is not expanding? Ok - so you're saying that there is a finite number of galaxies and an infinite empty space into which they are moving? Am I understanding your position correctly?

Yes. But, that “finite” number is super large. Maybe many times more than what we can currently see. Every time we build a bigger telescope, we see more distant galaxies. But just because there are a whole lot of them, that doesn’t mean there are an infinite number of them.

The question then becomes: why can't we see a variation in the density of galaxies (or the CMBR) which shows us where the edge is? Why can't we determine the direction to the center by observing the motion of the galaxies around us?

If you are on a particle inside a spherical explosion, and if the center and the outer edge are far enough away, you won’t be able to see either. You’ll see the other particles separating all around you, but you won’t know where you are within the expanding sphere.

If the universe is large enough, we’ll never see the “outer edge”, and we might not ever know if there is one.

We’re still stuck in the same situation we’ve always been stuck in. The further we look, there are galaxies all around us, so we don’t know where the “edge” is or even if there is one. The universe is pretty big, and about all we know is that we’re somewhere inside it. But that’s the same as what we knew 5,000 years ago.

Sam5
2004-Jan-27, 05:29 PM
Data, Sam,

I watched this thing about “expanding space” come about in the science media during the ‘80s and ‘90s. It was talked about more and more, the more superluminal galaxies were discovered. It is used only to try to keep nature from violating Einstein’s “c speed limit” rule. That’s all it is used for. I’ve seen some astronomers say, “the galaxies are stationary and not moving, but they are being carried along by expanding space.” This is just plain nuts.

There are no physics papers that explain how “space expands” or how it could “expand”. This is just a slogan, a nonsense slogan designed to keep nature from “violating” one of “Einstein’s Laws”. This is just plain nuts too. It’s as if some astronomers think of Einstein as “God”, and they claim nature “can not violate God’s laws”, which “God” wrote in the form of science papers in 1905 and 1916. This is crazy.

Taibak
2004-Jan-27, 09:02 PM
Data, Sam,

I watched this thing about “expanding space” come about in the science media during the ‘80s and ‘90s. It was talked about more and more, the more superluminal galaxies were discovered. It is used only to try to keep nature from violating Einstein’s “c speed limit” rule. That’s all it is used for. I’ve seen some astronomers say, “the galaxies are stationary and not moving, but they are being carried along by expanding space.” This is just plain nuts.

Why is it nuts? It's a perfectly good explanation for the fact that almost every observed galaxy is moving away from us and for why those that aren't (Andromeda and the Magellanic Clouds, for instance) are gravitationally bound to us. That would mean that either our galaxy is at the center of the universe, which is impossible, or that spacetime is expanding.

Incidentally, would you care to actually cite a specific, *current* reference that argues for superluminal galaxies? Twenty-year old documentaries aren't exactly great sources, espescially for a field like cosmology that's changed a lot over the last six years.

There are no physics papers that explain how “space expands” or how it could “expand”.

You mean besides the fact that it pops right out of Einstein's General Theory of Relativity? Einstein himself realised this possibility. Granted he thought it was wrong and introduced the Cosmological Constant to eliminate it, but, like a good scientist, changed his mind when Hubble proved that the universe was in fact expanding.

This is just a slogan, a nonsense slogan designed to keep nature from “violating” one of “Einstein’s Laws”. This is just plain nuts too. It’s as if some astronomers think of Einstein as “God”, and they claim nature “can not violate God’s laws”, which “God” wrote in the form of science papers in 1905 and 1916. This is crazy.

You need to brush up on both your science and your history here. Like I mentioned, Einstein's original theory argued for a static universe and *that* was proved wrong very quickly. Moreover, as any physicist will tell you General Relativity is flawed simply because it's incompatible with quantum mechanics. Not that Heisenberg and Plank were gods either, since quantum needs refinement to accomidate gravitation. Einstein's theories will eventually be replaced, just like Newton's were.

As for it being a slogan, let's look at the evidence:

In general, every galaxy in the universe is moving away from us. Those that aren't are gravitationally bound to the Milky Way.

If galaxies drifted aimlessly, we should see roughly equal numbers of galaxies moving towards us as away from us. We don't.

We can see the light from supposedly 'superluminal' galaxies, implying that they are travelling slower than the speed of light.

The Earth is not the center of the universe. Otherwise, we would only see young objects as we look deeper into space, not the oldest objects known to man.

To date, repeated experiments have shown that it is impossible to get *electrons* to travel at the speed of light without expending an *infinite* amount of energy. Thus, it should take a *lot* more energy to get even a small *galaxy* close to the speed of light.

Put these all together. The Earth can't be at the center of the universe, which means that we can't be at the source of the Big Bang. Therefore, there's no special reason why galaxies should be moving away from us and there's no evidence that galaxies move randomly. Also, experiments in particle accelerators have, for decades, all seem to say that it's impossible to accelerate even a low-mass object, like an electron, to the speed of light, simply because the acceleration decreases as the particle's speed approaches the speed of light. If you think about it, the basic laws of momentum make it equally impossible for a galaxies, which are much more massive than electrons, to acheive speeds even close to the speed of light from a simple explosion like you argue the Big Bang was.

The only possibilities that I can see here are that either the laws of inertia don't apply to galaxies *or* that space itself is expanding. Since I can't think of any good reason why large masses should behave differently than small masses, it must be space expanding.

Perhaps continental drift would provide a good analogy. Instead of galaxies, think about Eurasia and the Americas. They're not randomly drifting away from each other. The *Atlantic* is expanding, pushing them away from each other. Why can't something analogous be happening in space? Why can't the Big Bang be the beginning of that expansion rather than a literal explosion?

Sam5
2004-Jan-27, 09:21 PM
Why is it nuts? It's a perfectly good explanation for the fact that almost every observed galaxy is moving away from us and for why those that aren't (Andromeda and the Magellanic Clouds, for instance) are gravitationally bound to us.

That's fine. What you just said is NOT "nuts".

What is “nuts” about it is this is, one theoretical physicist told me what the galaxies are doing is “a change in distance without movement.”, and I think that is nuts.

Some of these guys claim “the galaxies aren’t moving, it is space that is expanding.”

Well, even if “space expands”, the galaxies are “moving”.

What you just said is NOT nuts, because you said, “almost every observed galaxy is moving away from us”, and that IS correct. But “a change in distance without motion” is NOT correct.

Taibak
2004-Jan-28, 03:40 AM
Why is it nuts? It's a perfectly good explanation for the fact that almost every observed galaxy is moving away from us and for why those that aren't (Andromeda and the Magellanic Clouds, for instance) are gravitationally bound to us.

That's fine. What you just said is NOT "nuts".

What is “nuts” about it is this is, one theoretical physicist told me what the galaxies are doing is “a change in distance without movement.”, and I think that is nuts.

Some of these guys claim “the galaxies aren’t moving, it is space that is expanding.”

Well, even if “space expands”, the galaxies are “moving”.

What you just said is NOT nuts, because you said, “almost every observed galaxy is moving away from us”, and that IS correct. But “a change in distance without motion” is NOT correct.

Well actually it all depends on how you define 'movement.' If you define it as a change in position relative to another source, then yes galaxies are moving away from us and you're right that the expansion of space drives this movement. That's certainly one way of looking at it, but not the only way.

The catch is that observers in any galaxy will get the same result we will - that galaxies are generally moving away from them. That can't happen without spacetime expanding. As such, it's not wrong to say that the galaxies aren't 'moving' - that they are not and were not being propelled by some force in the same sense that a kick propells a soccer ball or rockets propel the space shuttle. They're just being dragged along by space and time. It's the difference between saying that an object is changing its distance from another object and saying that the distance between two objects is changing itself and, consequently, the relative positions of the two objects. This is why the raisins-in-bread analgy or the spots-on-a-balloon analogy work fine.

On a related note, anyone know if it's theoretically possible for two galaxies to be at rest relative to each other? If I understand this right, they'd have to be gravitationally bound to compensate for the effects of spacetime expansion. However, that seems like it would in practice require them to either be orbiting each other, like binary stars, or gradually pull them towards each other. It seems like, in theory, that it should be possible for two galaxies to be travelling in the same direction relative to some distant object, but have their gravities pulling on each other with *exactly* the force needed to keep their relative distance constant as the intervening spacetime tried to expand.

Even so, I can't shake the feeling that the acceleration due to gravity should be much greater than the acceleration of spacetime at close distances and at long distances the effects of exansion would be much more pronounced than the effects of gravity. It would seem prohibitively difficult to get even a metastable relationship here. Am I totally off base here?

Sam5
2004-Jan-28, 04:04 AM
As such, it's not wrong to say that the galaxies aren't 'moving' - that they are not and were not being propelled by some force in the same sense that a kick propells a soccer ball....

You can’t say that. You’ve got absolutely no idea what started them to move in the first place, and no one does. We just built a big telescope one day and there they were already moving. No one knows why.

freddo
2004-Jan-28, 04:07 AM
As such, it's not wrong to say that the galaxies aren't 'moving' - that they are not and were not being propelled by some force in the same sense that a kick propells a soccer ball....

You can’t say that. You’ve got absolutely no idea what started them to move in the first place, and no one does. We just built a big telescope one day and there they were already moving. No one knows why.

So now you dispute the conclusions of our observations. We know more than you think Sam5...

Sam5
2004-Jan-28, 04:08 AM
This is why the raisins-in-bread analgy or the spots-on-a-balloon analogy work fine.

The center raisin doesn’t move and it’s at the center of the “expansion” of all the other raisins. That is a good analogy. So is Lamaitre’s “fireworks” analogy and Newton’s “projectile force” idea.

Sam5
2004-Jan-28, 04:09 AM
As such, it's not wrong to say that the galaxies aren't 'moving' - that they are not and were not being propelled by some force in the same sense that a kick propells a soccer ball....

You can’t say that. You’ve got absolutely no idea what started them to move in the first place, and no one does. We just built a big telescope one day and there they were already moving. No one knows why.

So now you dispute the conclusions of our observations. We know more than you think Sam5...

Ok, if you know why they are moving, then you tell us why. Is it some kind of secret?

The last book I read about it said it was due to some kind of “big bang”, with the universe expanding from a “dot” or a “point”. Has that idea changed? This is essentially Lamaitre’s 1927 “fireworks” theory and Newton’s “projectile force”.

freddo
2004-Jan-28, 04:17 AM
Ok, if you know why they are moving, then you tell us why. Is it some kind of secret?

Irellevant.. You said it was wrong to claim they're "not and were not being propelled by some force in the same sense that a kick propells a soccer ball...." In the absence of knowing whether a force existed or not - how can you possibly assert that this is wrong to say?

Sam5
2004-Jan-28, 04:24 AM
Ok, if you know why they are moving, then you tell us why. Is it some kind of secret?

Irellevant.. You said it was wrong to claim they're "not and were not being propelled by some force in the same sense that a kick propells a soccer ball...." In the absence of knowing whether a force existed or not - how can you possibly assert that this is wrong to say?

You said, “So now you dispute the conclusions of our observations. We know more than you think Sam5...”

Or were you just making that up?

I suspect, just like everyone else, you don't know why they are moving.

freddo
2004-Jan-28, 04:27 AM
I suspect, just like everyone else, you don't know why they are moving.
As I said, the why is beside the point. We have a pretty good idea on the how..

Taibak
2004-Jan-28, 04:29 AM
This is why the raisins-in-bread analgy or the spots-on-a-balloon analogy work fine.

The center raisin doesn’t move and it’s at the center of the “expansion” of all the other raisins. That is a good analogy. So is Lamaitre’s “fireworks” analogy and Newton’s “projectile force” idea.

Fair point about there being a raisin at the center of the loaf. I admit that's where the analogy breaks down. Still, it's salvageable simply because it's a good way to get one's brain around the idea of intervening space (the bread) expanding. However, the other two simply do not work with the Big Bang. The Big Bang was not an explosion, no matter what its name implies, so there is no projectile force. It was just the beginning of spacetime expansion.

The fireworks analogy doesn't work well because it uses different geometry than the universe. If you use the *entire* sphere, you have yourself a finite, three-dimensional object with a center. Tthat's a problem since the universe has neither a finite edge nor a center - it uses a very different method of expansion. Moreover, with a firework it's quite clear that an explosive force is pushing the sparks outward - there seems to be no such force driving the expansion of the universe. If you restrict yourself to the *surface* of the sphere, well, you're better off using the balloon for the sake of clarity. You're still dealing with what's clearly an explosive force rather than an expanding intervening distance. More importantly, you don't have a clearly defined surface. That's a problem because if GR is right, the universe *is* an infinite four-dimensional surface. Why model it with something that lacks such an important feature of the theory?

Tensor
2004-Jan-28, 04:35 AM
On a related note, anyone know if it's theoretically possible for two galaxies to be at rest relative to each other? If I understand this right,

...

relative to some distant object, but have their gravities pulling on each other with *exactly* the force needed to keep their relative distance constant as the intervening spacetime tried to expand.

I don't see any theoretical reason why the expansion can't be balanced by gravity.

Even so, I can't shake the feeling that the acceleration due to gravity should be much greater than the acceleration of spacetime at close distances and at long distances the effects of exansion would be much more pronounced than the effects of gravity.

Relative to whom? If your looking out very far, yes, spacetime expansion would appear much greater. But, remember, if the galaxies are close enough, the galaxie's movement due to expansion, from our point of view, would be about the same. It doesn't matter if the galaxies are close to us or at z=5, the expansion is still increasing at 50-100 kp/s/Mpc. Move out Andromeda another million light years and it would be about 1 Mpc away. It should be moving away at 50-100 km/s/Mpc due to expansion, but it would still probably be moving toward us, due to gravity (since is currently is moving toward us at 100 kps). I can see the distance between us and Andromeda, if moved a bit farther out, being at some point equal to the expansion value and therefore at rest to us.

It would seem prohibitively difficult to get even a metastable relationship here. Am I totally off base here?

I wouldn't guarentee how long it would stay that way, but I don't think you're off base here. It just don't think it would be a stable, long term, type relationship, IMHO.

Sam5
2004-Jan-28, 04:37 AM
This is why the raisins-in-bread analgy or the spots-on-a-balloon analogy work fine.

The center raisin doesn’t move and it’s at the center of the “expansion” of all the other raisins. That is a good analogy. So is Lamaitre’s “fireworks” analogy and Newton’s “projectile force” idea.

Fair point about there being a raisin at the center of the loaf. I admit that's where the analogy breaks down. Still, it's salvageable simply because it's a good way to get one's brain around the idea of intervening space (the bread) expanding. However, the other two simply do not work with the Big Bang. The Big Bang was not an explosion, no matter what its name implies, so there is no projectile force. It was just the beginning of spacetime expansion.

I think the bread expands because of some kind of gas, maybe CO2. Are you suggesting that there is some kind of yeast in space that is releasing CO2 gas that is causing the galaxies to move apart?

What happened to the “big bang” theory and the big explosion from that little point? That theory was taught for about 65 years.

Have they changed it to the "big poof"?

I think Astronomy magazine had a big contest a few years ago, wanting people to give it a new name. I guess astronomy theory is now up to holding contests about it in Astronomy magazine.

russ_watters
2004-Jan-28, 04:39 AM
I think the bread expands because of some kind of gas, maybe CO2. Are you suggesting that there is some kind of yeast in space that is releasing CO2 gas that is causing the galaxies to move apart? Sam, you need to look up the word "analogy" in the dictionary.

By the way - the way it applies to the theory isn't that just the center rasin isn't moving: none of the rasins are moving. The bread is expanding between the rasins, which makes it appear to every rasin that every other rasin is moving away from it.

Also - The Sam5 Model of the Universe has a pretty big flaw: even in your model, we can calculate an age. And when we start looking at objects that are far enough away that they are close to that age, we should start seeing the structure you propose. But we don't.

Taibak
2004-Jan-28, 04:43 AM
The last book I read about it said it was due to some kind of “big bang”, with the universe expanding from a “dot” or a “point”. Has that idea changed? This is essentially Lamaitre’s 1927 “fireworks” theory and Newton’s “projectile force”.

No, the idea is still that the universe still expanded out of a point-like singularity. What has changed, however, is the idea that the singularity just contained matter and energy which became unstable and exploded. I think it's more accurate to say that over the past seven or so decades, physicists have realised that GR allows for spacetime itself to expand and that this expansion would have had to have started with the Big Bang. As such, that original point-like singularity contained space and time as well as matter and energy.

We don't know what started the expansion or what was outside that singularity. There are a lot of theories that seek to explain these things, but so far none of them have been proven. None of them include any kind of explosive force or 'projectile force' though.

Sam5
2004-Jan-28, 04:45 AM
I think the bread expands because of some kind of gas, maybe CO2. Are you suggesting that there is some kind of yeast in space that is releasing CO2 gas that is causing the galaxies to move apart? Sam, you need to look up the word "analogy" in the dictionary.

I think Lemaitre’s fireworks analogy, which lasted for 65 years, is much better than the cosmic muffin analogy.

freddo
2004-Jan-28, 04:46 AM
I think the bread expands because of some kind of gas, maybe CO2. Are you suggesting that there is some kind of yeast in space that is releasing CO2 gas that is causing the galaxies to move apart?
http://dictionary.reference.com/search?q=analogy

Sam5
2004-Jan-28, 04:47 AM
The last book I read about it said it was due to some kind of “big bang”, with the universe expanding from a “dot” or a “point”. Has that idea changed? This is essentially Lamaitre’s 1927 “fireworks” theory and Newton’s “projectile force”.

No, the idea is still that the universe still expanded out of a point-like singularity. What has changed, however, is the idea that the singularity just contained matter and energy which became unstable and exploded. I think it's more accurate to say that over the past seven or so decades, physicists have realised that GR allows for spacetime itself to expand and that this expansion would have had to have started with the Big Bang.

What do you mean “GR allows”? You mean GR didn’t allow it 10 and 20 years ago? Does GR change with time?

Jobe
2004-Jan-28, 04:55 AM
As such, it's not wrong to say that the galaxies aren't 'moving' - that they are not and were not being propelled by some force in the same sense that a kick propells a soccer ball....

You can’t say that. You’ve got absolutely no idea what started them to move in the first place, and no one does. We just built a big telescope one day and there they were already moving. No one knows why.

So now you dispute the conclusions of our observations. We know more than you think Sam5...

Ok, if you know why they are moving, then you tell us why. Is it some kind of secret?

The last book I read about it said it was due to some kind of “big bang”, with the universe expanding from a “dot” or a “point”. Has that idea changed? This is essentially Lamaitre’s 1927 “fireworks” theory and Newton’s “projectile force”.

You believe in the steady state universe? :rollseyes: Figures.

How do you explain CMB radiation?

Sam5
2004-Jan-28, 04:57 AM
As such, it's not wrong to say that the galaxies aren't 'moving' - that they are not and were not being propelled by some force in the same sense that a kick propells a soccer ball....

You can’t say that. You’ve got absolutely no idea what started them to move in the first place, and no one does. We just built a big telescope one day and there they were already moving. No one knows why.

So now you dispute the conclusions of our observations. We know more than you think Sam5...

Ok, if you know why they are moving, then you tell us why. Is it some kind of secret?

The last book I read about it said it was due to some kind of “big bang”, with the universe expanding from a “dot” or a “point”. Has that idea changed? This is essentially Lamaitre’s 1927 “fireworks” theory and Newton’s “projectile force”.

You believe in the steady state universe? :rollseyes: Figures.

How did you get that out of what I said?

Taibak
2004-Jan-28, 05:09 AM
Even so, I can't shake the feeling that the acceleration due to gravity should be much greater than the acceleration of spacetime at close distances and at long distances the effects of exansion would be much more pronounced than the effects of gravity.

Relative to whom? If your looking out very far, yes, spacetime expansion would appear much greater. But, remember, if the galaxies are close enough, the galaxie's movement due to expansion, from our point of view, would be about the same. It doesn't matter if the galaxies are close to us or at z=5, the expansion is still increasing at 50-100 kp/s/Mpc. Move out Andromeda another million light years and it would be about 1 Mpc away. It should be moving away at 50-100 km/s/Mpc due to expansion, but it would still probably be moving toward us, due to gravity (since is currently is moving toward us at 100 kps). I can see the distance between us and Andromeda, if moved a bit farther out, being at some point equal to the expansion value and therefore at rest to us.

Well, that's sort of what I'm asking about. For the sake of simplicity, say the galaxies are 1 Mpc apart. Let's assume also that the intervening spacetime expands at 100 km/s/Mpc. As such, an observer in one galaxy would see the other galaxy receding at 100 km/s if you ignore the effects of gravity. However, when you turn the gravity back on, it will cause the galaxies to accelerate towards each other, regardless of whether or not you model gravity as a force or as curvature. Given enough time, our observer will measure that the other galaxy is approaching hers. Ergo, gravity wins out over expansion. On the other hand, she might measure that the galaxy is receding, implying that expansion should win.

I agree with your basic argument that we're talking only about two objects that are temporarily at rest relative to each other. This would be necessarily unstable, given enough time. But taking this a step further, this would imply that if the net gravitational pull of the two galaxies caused them to move towards each other at 100 km/s *and* the changes in that speed were *exactly* offset by the accelerating rate of expansion you should be able to make this stable indefinitely. What I'm still not sure about is how time - which should be expanding along with space - factors into this, if it does at all.

Granted, the presence of other sources of gravity in the universe should make this ideal situation almost impossible to acheive, but that's the fun of theory. :-)

Taibak
2004-Jan-28, 05:29 AM
What do you mean “GR allows”? You mean GR didn’t allow it 10 and 20 years ago? Does GR change with time?

Well, the underlying physics don't change, but our understanding of the physics sure as heck does. I mean, Einstein didn't just write down the theory and *wham* the entire population of the Earth understood general relativity and all of its consequences. Black holes are a good example. Karl Schwarzschild first solved Einstein's Equations during World War I - in the trenches no less - but he did so only for a sphereically symmetric, electrically neutral, non-rotating object in otherwise empty space. Out of this came the first theoretical predictions of black holes. Even so, it was *decades* before the first observational evidence for the existence of black holes was found (amongst other things, artificial satellites and X-Ray astronomy needed to be invented). Since WWI, more solutions to Einstein's Equations have been found (slowly rotating objects, electrically charged objects, etc.) and each time a new solution is found, our understanding of general relativity and the physics of black holes advances. On the observational side, you'll find books written as late as the 1960's that treat black holes as purely theoretical. You'll also find books written as late as 1980's that have no idea what quasars are. It's only been comparatively recently that we've figured out that they're the matter jets streaming out of black holes. Granted we still have no idea what causes these jets, but we're working on it.

Taibak

PS: Quasars are great here for another reason. They're the same type of objects as blazars and Seyfert galaxies and only their orientation relative to the Earth is different. But they have three different names because they were originally believed to be three different types of objects.

Tensor
2004-Jan-28, 11:21 AM
Well, that's sort of what I'm asking about. For the sake of simplicity, say the galaxies are 1 Mpc apart. Let's assume also that the intervening spacetime expands at 100 km/s/Mpc. As such, an observer in one galaxy would see the other galaxy receding at 100 km/s if you ignore the effects of gravity. However, when you turn the gravity back on, it will cause the galaxies to accelerate towards each other, regardless of whether or not you model gravity as a force or as curvature. Given enough time, our observer will measure that the other galaxy is approaching hers.

I'd say that would depend on the masses of the galaxies. If they were close to the same size and about the right mass to balance the expansion. They may not approach each other, they may stay balanced.

Ergo, gravity wins out over expansion. On the other hand, she might measure that the galaxy is receding, implying that expansion should win.

I agree with your basic argument that we're talking only about two objects that are temporarily at rest relative to each other. This would be necessarily unstable, given enough time. But taking this a step further, this would imply that if the net gravitational pull of the two galaxies caused them to move towards each other at 100 km/s *and* the changes in that speed were *exactly* offset by the accelerating rate of expansion you should be able to make this stable indefinitely.

If, as you point out below, you ignore any other gravitational influences. I didn't make that clear in my post, but other galaxies would eventually cause it to be unstable. Thanks for pointing that out.

What I'm still not sure about is how time - which should be expanding along with space - factors into this, if it does at all.

I'd have to go back in and look, but I don't think time expands in the same sense as the spatial dimensions, since it enters the equations with a different sign.

Granted, the presence of other sources of gravity in the universe should make this ideal situation almost impossible to acheive, but that's the fun of theory. :-)

Noted and thanks.