My favourite relativity paradox

[bunny]

A recent post made me remember studying relativity and a bunch of supposed "paradoxes" they always throw at undergraduates to make them think about it. This one often doesnt make the standard lists and some people here may enjoy trying to figure it out:

A man puts a 30m pole vault on his shoulder and stands in a 20m long barn with doors open at each end. Surprise, surprise the pole sticks out on either side. Then he runs off, leaving you to stay by the barn. He then comes running back at a speed very close to the speed of light (say 99% of the speed of light or something) and zooms through the barn. Because you have studied relativity, you know that objects get shorter as they move faster and so in that precise instant that he is in the middle of the barn, you operate a machine which slams the doors shut, then opens them again while he is inside (the length of his pole is easily less than 20m at this speed) he then zooms off into the distance and you think "Wow, this relativity stuff really works - I shut the door".

Then he comes back and you tell him what happened. His response is that this is impossible as relative to his frame of reference, the barn was speeding towards him at very close to the speed of light and had therefore contracted and was nowhere near 20m long (let alone 30m long which it would need to be to accomodate his pole). Thus, he says, you couldnt possibly have closed the doors while I was inside.

What's the resolution to the paradox?

[Borodog]

The doors don't close at the same time for him.

[PokerPadawan]

Actually, the answer to this paradox is that the pole is not perfectly rigid. The information that the pole has hit the closed doors cannot propagate backward down the pole faster than the speed of light. This causes the pole to compress, making it short enough to fit inside the barn at the instant that the back doors close. After that, it will be held squeezed inside the barn (assuming infinite strength doors, of course).

[Borodog]

[ QUOTE ]
Actually, the answer to this paradox is that the pole is not perfectly rigid. The information that the pole has hit the closed doors cannot propagate backward down the pole faster than the speed of light. This causes the pole to compress, making it short enough to fit inside the barn at the instant that the back doors close. After that, it will be held squeezed inside the barn (assuming infinite strength doors, of course).

[/ QUOTE ]

That's not the scenario described. The scenario described is that the doors, which are on both sides of the barn, are closed with the pole entirely in the barn and then reopened before it strikes the back doors, thus exiting the barn without ever having touched the doors.

[Matt R.]

[ QUOTE ]
Actually, the answer to this paradox is that the pole is not perfectly rigid. The information that the pole has hit the closed doors cannot propagate backward down the pole faster than the speed of light. This causes the pole to compress, making it short enough to fit inside the barn at the instant that the back doors close. After that, it will be held squeezed inside the barn (assuming infinite strength doors, of course).

[/ QUOTE ]

Borodog is right. The pole contracts from your point of view -- but the barn contracts from the perspective of the man moving at .99c. The pole doesn't contract according to the man moving at .99c -- it is at its rest length.

If you use the Lorentz tranformation for the time coordinate of the man moving at .99c, you see that the 2nd door the man passes through closes before the first door. The question states that the doors re-open before the pole touches the doors. So, the 2nd door re-opens with enough time for the man to pass through from his perspective, and the 1st door remains open while the 2nd door is shut (leaving him with enough room to fit the pole in the barn).

Edit -- Oops... what Borodog said.

[PokerPadawan]

Oops, I didn't see the part about it opening again. That's the lame version. I like the version where the doors are kept shut, since it requires a little outside of the box thinking. And of course you shouldn't say that the pole is entirely in the barn, because it never is.

[bunny]

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Oops, I didn't see the part about it opening again. That's the lame version. I like the version where the doors are kept shut, since it requires a little outside of the box thinking. And of course you shouldn't say that the pole is entirely in the barn, because it never is.

[/ QUOTE ]

It is entirely inside the barn according to observers outside - they see the doors both shut with the man and the pole contained inside for an instant.

[PokerPadawan]

That's just because the only information about the pole they can receive is the light from it. That doesn't mean it really was inside the barn. The whole point of this aspect of the paradox is that information that an observer sees is tainted by the fact that light can only move at a fixed, finite velocity.

[bunny]

[ QUOTE ]
That's just because the only information about the pole they can receive is the light from it. That doesn't mean it really was inside the barn. The whole point of this aspect of the paradox is that information that an observer sees is tainted by the fact that light can only move at a fixed, finite velocity.

[/ QUOTE ]

No. The point is that there is no such concept as whether it "really is" in the barn or not. There is no absolute frame of reference. For some people it is, for some people it isnt. The barn, for example, has a frame of reference in which both doors are closed and the runner and pole are within the barn's limits.

[PokerPadawan]

I'm not going to argue this any longer. This is mostly just a semantic issue. We are arguing what "really" means. The pole was never in the barn because it was never compressed for real, just *visually* length contracted. You can attach some sort of "compression" monitor to the pole and confirm this after the experiment. Just understand that the pole is never really compressed. You absolutely know this because there is no force to cause the compression. The object is merely moving fast, so it *looks* weird. But don't worry about it too much. Just say whatever your prof says. /images/graemlins/grin.gif

If a star goes supernova today, but it is 100,000 light years away, we will think it is still there for the next 100,000 years. That doesn't mean it really is.

[PokerPadawan]

I should also say that you can put a large display on the compression monitor and read it from a distance after it comes out of the barn. You don't need to be in the pole's frame to read it.

[PokerPadawan]

I've seen more of your posts and now realize how keen you are on the concept of no absolute frame of reference. I'm not contradicting that idea here. This paradox is not a very good example of that. My astronomy training has taught me that it is arrogant to think that observing something from a distance gives you the full story.

[Borodog]

Lorentz contraction is not a "trick of the light" so to speak. The contraction of the ladder is not due to forces exerted on it, but rather to the relativity of simultaneity. From Rindler:

"The most striking feature of the Lorentz transformation is the transformation of time, which exhibits the relativity of simultaneity: events with equal t [the time coordinate in one inertial frame] do not necessarily correspond to events with equal t' [the time coordinate in a different inertial frame]." -- Wolfgang Rindler, Introduction to Special Relativity, 2nd Ed. p.16

And,

". . . the length L of a body in the direction of its motion with uniform velocity v is reduced by a factor (1-v^2/c^2)^(1/2)." -- p.25

This is where I think you are becoming confused:

"This length contraction is a kind of velocity perspective effect (in Weyl's phrase)--analogous to the visual foreshortening of a stationary rod that is viewed from a direction not orthogonal to the rod. For our world-map of the moving rod we pick what in the rod's frame are later events at its back than at its front, so that the back appears closer to the front. But of course, nothing at all has happened to the rod itself. Just as the proper length of the stationary rod can be restored by bringing our eye into a suitable position relative to it, so that of the moving rod can be retored by moving our eye along with it.

Nevertheless, relativistic length contraction is no 'illusion': it is real and, in principle, usable. For example, just as a slanting rod can be placed in the space between two parallel planes, which it would not fit perpendicularly, so a moving rod can be momentarily confined in a space which it would not fit when at rest." -- p.25 (Emphasis added.)

[PokerPadawan]

I have no confusion -- the issue is simple if you just draw it on a space-time diagram. Your quote in bold is very misleading, since it is ignoring those very same simultaneity issues that cause this effect.

[PokerPadawan]

Just so I don't sound like such a jerk, here is the solution to what you are talking about.

Say you have a pole moving at velocity v, with x- and y-components v_x and v_y, toward a hole in a wall that is smaller than the pole. Now say that the wall is flat along the x-axis, so that the rate at which the pole is moving toward the wall is just v_y. You might think it will pass through because the pole is physically length contracted. This is incorrect. The wall, according the pole's frame, has tilted, by an angle theta = v_x v_y / sqrt(1 - v_x^2). (I'm using velocities in units of c.) This is due purely to simultaneity and can be verified with appropriate Lorentz tranformations. The pole will actually pass through the hole front first, instead of sideways, like you might think.

Length contraction is purely a conceptual tool that helps humans do these sorts of tranformations in their heads. /images/graemlins/wink.gif

[Borodog]

I'm not sure why you changed the situation. The original situation is quite clear. Just to elaborate, I am sitting at rest in front of a large measuring stick with a superduper high speed camera. A rod of length 1m is fired from the left to the right at relativistic speeds. The rest length of the rod is illustrated on the left, and my camera image on the right:

rest length |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
-------- <font color="white"> ........................... </font> ----

Furhtermore, I have arranged to have two timed superduper hgih speed actuators fire two plates simultaneously _in my frame_ at two particular locations along the meter stick, less than 1 meter apart. Now my camera records this:

rest length |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
-------- <font color="white"> ........................... </font> | ---- |

In other words, the rod is entirely contained in a space less than 1 meter in length. I cannot do this by any trick of the light. I can do this because simultaneity is relative; time is different for me and the rod.

When you say that "Of course the ladder is never really in the barn" you are assigning a preferential reference frame to the ladder, implying that it's frame is somehow more "real" than the barn's frame. It is not. That's the entire point.

[Trantor]

Nonsense! It is not semantics it is how the real world is....and it is not as you think it is.The pole reeally is in the barn between 2 closed doors in one frame and really passes through a shorter barn in the pole carrier's frame.

[PokerPadawan]

OK, then, I'm done with this thread. There is a basic lack of deeper understanding of physics here, which I can't remedy apparently. Think whatever the hell you want. There is often a preferred reference frame for problems. The idea that there isn't applies only under certain circumstances. I just can't fight your dogma. I've had three courses in relativity, including a graduate course at Harvard, and done astrophysics research for 6 years now. I absolutely know how to think about physical problems.

[Borodog]

Dude, chill. The problem is a straightforward problem in special relativity. There is no preferred reference frame here. The ladder is in the barn with both doors closed while I'm looking at it. Go ask the instructors of your three courses in relativity, including the graduate course at Harvard, whether or not the ladder is actually in the barn in the barn's rest frame.

I have a Ph.D. in astrophysics too. It is not a dick measuring party, and there is no need to get all pissy.

[PokerPadawan]

I'm not pissy, just disheartened.

[Borodog]

Because you can't demonstrate why I'm wrong, and I won't knuckle under to your assertions and appeal to authority?

[PokerPadawan]

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Because I can't understand why I'm wrong, and I won't open my mind to your explanation?

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FYP

[Borodog]

What explanation? All you presented was handwaving, and incorrect handwaving at that.

Why don't you write the authors and the publishers of every special relativity text in existence and explain to them how they're all wrong?

If I'm so wrong, it should be relatively easy for you to illustrate why it's impossible for me to close the doors of the barn while an object that is clearly shorter than the barn is inside. I'm waiting.

It should also be a trivial matter for you to email your former professors and have them put me in my place. Why don't you do that?

[TomCollins]

I hope you went to MIT, Borodog.

[Borodog]

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I hope you went to MIT, Borodog.

[/ QUOTE ]

Nope. I went to humble NC State. But I know how to put a relativistic ladder in a barn.

[PokerPadawan]

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It should also be a trivial matter for you to email your former professors and have them put me in my place. Why don't you do that?


[/ QUOTE ]

That would be an appeal to authority.

[Borodog]

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It should also be a trivial matter for you to email your former professors and have them put me in my place. Why don't you do that?


[/ QUOTE ]

That would be an appeal to authority.

[/ QUOTE ]

So you don't want to hear their response.

[PokerPadawan]

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I hope you went to MIT, Borodog.

[/ QUOTE ]

At least then I'd understand his antagonism. /images/graemlins/wink.gif

[PokerPadawan]

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[ QUOTE ]
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It should also be a trivial matter for you to email your former professors and have them put me in my place. Why don't you do that?


[/ QUOTE ]

That would be an appeal to authority.

[/ QUOTE ]

So you don't want to hear their response.

[/ QUOTE ]

It's a joke .... /images/graemlins/confused.gif

[Borodog]

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I hope you went to MIT, Borodog.

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At least then I'd understand his antagonism. /images/graemlins/wink.gif

[/ QUOTE ]

Lol. Read the thread. Who has the antagonism again?

[PokerPadawan]

OK, let me try one last thing. I believe you are being too arrogant in your definition of reality. You are misapplying the principle of no preferred frame to this problem. If you were observing the pole go through the barn, all you could say was that it *looks* like it was shut inside for a few nanoseconds. You wouldn't normally presume to *know* that it was.

Now, any scientist worth his/her salt would say, "OK, I know that pole was moving very nearly at c, so I should do an inverse Lorentz tranformation to figure out the exact sequence of events." After doing this, they would find that the doors didn't close simutaneously. Why would the scientist do that? Because they would know that relativistic travel distorts things.

Here is another example, using what I'm talking about, but with time dilation. Your body is being bathed in muons right now, originating from nuclear reactions due to cosmic rays hitting the atmosphere. The normal lifetime of a muon is about 2.2 microsecs. But it takes much longer than this to get to the ground. Now a scientist wouldn't see all these muons and assume that they came from 2.2 light-microsecs away. No, they know that they are traveling at near c, and so correct for the time dilation to find that they come from the upper atmosphere. You can't just say that there is no preferred frame every time. Science often prefers the moving frame, not the lab frame. In this case, scientists absolutely know that the muon lifetime in 2.2 us, so they when they see a muon live much longer, they know it was traveling near c, not that this was a freak muon with different physics.

The pole/barn is similar in that we know that the pole is not a freak of physics. It can't physically fit in the barn, thus the scientist would naturally inverse tranform the sequence of events.

Note that none of this is to be confused with general relativity, in which the physical size of things can actually change due to the flexing of spacetime underneath it, but without actual compression or stretching. (See gravity waves, for example.)

So is the pole in the barn or isn't it? You can say it is, just because it appears that way in the lab frame. But no one who isn't argumentative and who knows relativity would say that it *really* is any more than you would say that the lifetime of the muon is *really* 3 ms if it is traveling near c. Or any more than you would say that we know for sure that a star is still alive and not gone supernova, if it is 100,000 light years away.

[PokerPadawan]

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I hope you went to MIT, Borodog.

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At least then I'd understand his antagonism. /images/graemlins/wink.gif

[/ QUOTE ]

Lol. Read the thread. Who has the antagonism again?

[/ QUOTE ]

I'm frustrated because I can't seem to explain this, not because I have an overwhelming desire to prove someone wrong. I really couldn't care less who is right. I just want you to understand what I'm trying to say. You just can't seem to get it. You keep making irrelevant statements, repeating the same misapplied generalities, and being generally mocking in your tone, as if you are hoping to prove that you are right and that I'm a moron for not understanding basic relativity. You remind me of the engineers who used to take my upper-level physics classes for fun. They would mock the teacher about some inane detail and totally miss the point, such as mockingly pointing out that the prof missed a subscript somewhere. Or conversely they would get into philosophical discussions in the middle of class and not shut up about it until class had ended and the prof had gotten nothing done. They annoyed the crap out of us physics students, who needed to learn the stuff to move on to the next class.

If you think you know physics so well, why did you quit doing astrophysics?

[Matt R.]

I have no Ph.D. in astrophysics. I have only taken one course over special relativity.

That being said, everything that I have learned regarding special relativity contradicts what you've posted in this thread. The professor for my SR class actually would make it a point to drill the "misconceptions" about relativity which you are arguing for out of our heads. Maybe you have a deeper understanding about special relativity that I won't get to until graduate level courses. But, I don't understand why textbooks and my professor would argue the opposite -- only to flip-flop in more advanced texts/classes saying "guess what, lorentz contraction doesn't *really* happen."

[bunny]

[ QUOTE ]
The pole/barn is similar in that we know that the pole is not a freak of physics. It can't physically fit in the barn...

[/ QUOTE ]

This statement goes to the core of where I disagree with you. My understanding of relativity (also from 2 undergraduate and 1 postgraduate course) says that this is an incorrect statement.

The correct statement is "It can't physically fit in the barn when at rest."

In other words - there is no answer to the question "How long is the pole?" Our language and everyday experience suggests that length is an inherent physical property - in actuality it isnt. Objective reality is stranger than that - the pole has no fundamental or "real" length.

[PokerPadawan]

[ QUOTE ]
But, I don't understand why textbooks and my professor would argue the opposite -- only to flip-flop in more advanced texts/classes saying "guess what, lorentz contraction doesn't *really* happen."

[/ QUOTE ]

Grrrrr, that's not what I'm saying at all. Of course contraction is real, but it is apparent, not intrinsic. The problem is, we can only get information from objects at lightspeed, so we have no way of not seeing the contraction. I think basic textbook relativity must encourage overly simplistic thinking. Similar to when you are taught that the acceleration of body in a gravitational field of a point mass is a = Gm/r^2. This equation does not have to be true in general; it just so happens to be to within a very high experimental accuracy. But the textbooks don't say anything about this. You have to just learn a lot of physics before you realize it is a coincidence that inertial mass equals gravitational mass.

[PokerPadawan]

[ QUOTE ]
[ QUOTE ]
The pole/barn is similar in that we know that the pole is not a freak of physics. It can't physically fit in the barn...

[/ QUOTE ]

This statement goes to the core of where I disagree with you. My understanding of relativity (also from 2 undergraduate and 1 postgraduate course) says that this is an incorrect statement.

The correct statement is "It can't physically fit in the barn when at rest."

In other words - there is no answer to the question "How long is the pole?" Our language and everyday experience suggests that length is an inherent physical property - in actuality it isnt. Objective reality is stranger than that - the pole has no fundamental or "real" length.

[/ QUOTE ]

This I agree with, mostly. My statement was misleading.

[Matt R.]

You keep saying the pole is only "visually" length contracted in your posts. I have very recently answered several problems for my special relativity class (&lt; 1 month ago) regarding what an extended object looks like to a single observer. I'm actually looking at an old homework problem right now which deals with this.

After doing the calculations you see that a lorentz contracted pole moving at you looks *longer* than the transformed length. This is due to (as you mentioned earlier) the propagation of light to the observer -- the light from the "back" end of the pole travels a longer distance and is emitted before the light from the front end.

BUT, once you take this difference into account -- the propagation of information at light speed toward the observer -- you see that the TRUE length from the reference frame of the observer is the lorentz contracted length.

I have the proof sitting right here in front of me (graded and all -- so unless the prof graded it incorrectly it is correct). This proof *specifically* takes into account the propagation of information to the observer. I think, without rereading all of your posts, that this is what you were arguing, that the contraction is purely due to these visual distortions. The math I'm looking at now shows otherwise.

[PokerPadawan]

Are you making the distinction between a pole moving sideways across your field of view and a pole moving toward you? The effects are different. I'm imagining the pole moving sideways.

[Metric]

I don't know if this thread needs another point of view, but perhaps I can clarify something: The laws of physics are Lorentz invariant (ignoring the subtle details of GR for the moment). That is, if I ask a Lorentz invariant question, relativity gives me a Lorentz invariant answer. The difficulty raised by the question "is the pole ever fully in the barn" is that it is not a Lorentz invariant question, and thus you should not expect a Lorentz invariant answer. This is what Borodog and others are saying. To answer the question without ambiguity you must break Lorentz invariance by specifying a reference frame. You are claiming that there is a "natural" reference frame to do this -- but of course this depends on your preference for what is natural! With regards to your muon example -- this is another case of picking one frame of reference that appears "natural" to the problem, but nevertheless it is still merely convention. If for some reason I wanted to re-define all particle half-lives in the frame of reference in which the particles are moving at 1/2 c because it was "natural" for some other purpose, nothing would stop me -- it would be equally valid, but perhaps cumbersome to think about and perform calculations with.

Hope this helps...

[Matt R.]

[ QUOTE ]
Are you making the distinction between a pole moving sideways across your field of view and a pole moving toward you? The effects are different. I'm imagining the pole moving sideways.

[/ QUOTE ]

The question from the homework has the pole moving sideways across the observer's field of view (not directly at him/her).

[Borodog]

[ QUOTE ]
OK, let me try one last thing. I believe you are being too arrogant in your definition of reality. You are misapplying the principle of no preferred frame to this problem. If you were observing the pole go through the barn, all you could say was that it *looks* like it was shut inside for a few nanoseconds. You wouldn't normally presume to *know* that it was.

Now, any scientist worth his/her salt would say, "OK, I know that pole was moving very nearly at c, so I should do an inverse Lorentz tranformation to figure out the exact sequence of events." After doing this, they would find that the doors didn't close simutaneously. Why would the scientist do that? Because they would know that relativistic travel distorts things.

Here is another example, using what I'm talking about, but with time dilation. Your body is being bathed in muons right now, originating from nuclear reactions due to cosmic rays hitting the atmosphere. The normal lifetime of a muon is about 2.2 microsecs. But it takes much longer than this to get to the ground. Now a scientist wouldn't see all these muons and assume that they came from 2.2 light-microsecs away. No, they know that they are traveling at near c, and so correct for the time dilation to find that they come from the upper atmosphere. You can't just say that there is no preferred frame every time. Science often prefers the moving frame, not the lab frame. In this case, scientists absolutely know that the muon lifetime in 2.2 us, so they when they see a muon live much longer, they know it was traveling near c, not that this was a freak muon with different physics.

The pole/barn is similar in that we know that the pole is not a freak of physics. It can't physically fit in the barn, thus the scientist would naturally inverse tranform the sequence of events.

Note that none of this is to be confused with general relativity, in which the physical size of things can actually change due to the flexing of spacetime underneath it, but without actual compression or stretching. (See gravity waves, for example.)

So is the pole in the barn or isn't it? You can say it is, just because it appears that way in the lab frame. But no one who isn't argumentative and who knows relativity would say that it *really* is any more than you would say that the lifetime of the muon is *really* 3 ms if it is traveling near c. Or any more than you would say that we know for sure that a star is still alive and not gone supernova, if it is 100,000 light years away.

[/ QUOTE ]

Me arrogant in my definition of reality? Pot? Kettle?

Now you are really starting to piss me off. This post is the most profoundly incorrect piece of claptrap I have seen in quite some time. Relativity provides a profoundly different view of the world. Time and distance are different in different inertial frames. That is the POINT of the Lorentz transformation. And if the distance between two points is different in two frames, then by God the length of a frigging ladder or rod with ends located at those points is different in those two frames. It's not a trick of light travel time. Simultaneous events in my frame are not simultaneous in your frame. In the ladder frame the rear doors of the barn close and then open before the front doors do. The rear doors close while the front of the ladder is in the barn and then open, allowing you and the ladder to pass through, and then the front doors close and then open while the rear of the ladder is in the barn. But in my reference frame these two events are simultaneous. The doors close simultaneously with the ladder entirely contained, momentarily, within the barn.

"Nevertheless, relativistic length contraction is no 'illusion': it is real and, in principle, usable. For example, just as a slanting rod can be placed in the space between two parallel plates which it would not fit perpendicularly, so a moving rod can be momentarily confined in a space which it would fit when at rest. Apart from the practical difficulties involved, we could verify length contraction as follows. A yard stick Y is at rest in a frame S" relative to which two identical rods PQ and P'Q' traveling at equal speeds in opposite directions (see Fig. 5). It is not difficult to imagine a device which leaves a mark on Y where the left end-points P and P' meet, and also one where the right end-points Q and Q' meet. The distance between these marks would be found to be less than the proper length of the rods. Note that, whereas in S' the coincidences (P,P') and (Q,Q') occur simultaneously, by symmetry, in the rest frame S of PQ the coincidence (P,P') occurs before (Q,Q'), and conversely in S', the rest frame of P'Q'. This is an obvious criterion for P'Q' to be shorter than PQ in S, and of the converse in S'. Thus our example illustrates not only the reality and the symmetry of length contraction, but also its relation to the relativity of simultaneity."

<font color="white">=======</font>P'<font color="white">======</font>Q'
<font color="white">=======</font>========----&gt;<font color="white">======</font>P<font color="white">=======</font>Q
<font color="white">=====================</font>&lt;----=========
|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_ |_|_|_| Y

<font color="white">===================</font>Fig. 5

Wolfgang Rindler, Introduction to Special Relativity, 2nd. Ed. p. 25

[Borodog]

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I hope you went to MIT, Borodog.

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At least then I'd understand his antagonism. /images/graemlins/wink.gif

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Lol. Read the thread. Who has the antagonism again?

[/ QUOTE ]

I'm frustrated because I can't seem to explain this, not because I have an overwhelming desire to prove someone wrong. I really couldn't care less who is right. I just want you to understand what I'm trying to say. You just can't seem to get it. You keep making irrelevant statements, repeating the same misapplied generalities, and being generally mocking in your tone, as if you are hoping to prove that you are right and that I'm a moron for not understanding basic relativity. You remind me of the engineers who used to take my upper-level physics classes for fun. They would mock the teacher about some inane detail and totally miss the point, such as mockingly pointing out that the prof missed a subscript somewhere. Or conversely they would get into philosophical discussions in the middle of class and not shut up about it until class had ended and the prof had gotten nothing done. They annoyed the crap out of us physics students, who needed to learn the stuff to move on to the next class.

If you think you know physics so well, why did you quit doing astrophysics?

[/ QUOTE ]

You sir, are an insulting jerk, who it would seem indeed does NOT understand basic relativity. I am not the one who was mocking anyone in this thread. I have carefully explained my thinking several times, which you have always asserted is wrong, but without showing why. I even asked you to check with your professors, all three of them, yet you refuse. I can only speculate about the reason. Your behavior has been atrocious, and indeed it is you who reminds me of the student who believes he has has a deeper understanding of the concepts than others, but has in reality missed something truly profound.

I left astrophysics because it's impossible to get a job in astrophysics without taking taxpayer money, which I have become morally opposed to. It would appear that your excuse will eventually be incompetence coupled with an inability to collaborate well with others.

[PokerPadawan]

Thank you, Metric. This makes a lot of sense to me. I can see that a lot of my statements have an inherent bias toward certain reference frames. It actually sickens me that I've wasted so much time arguing about this. I don't really even like the question of whether the pole is inside the barn or not, purely because of its non-invariant (relative) nature. It feels more like the argument, "What is truth?" Or the other arguments in this forum about theist vs. atheist.

[gumpzilla]

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Lorentz contraction is not a "trick of the light" so to speak. The contraction of the ladder is not due to forces exerted on it

[/ QUOTE ]

Really? The electric field of a charge moving at relativistic velocities gets foreshortened. I'm pretty sure that Lorentz noticed this and then correctly proposed Lorentz contraction as a fix to explain the Michelson-Morley result. This is probably a bit of an oversimplification, but I don't think it's incorrect to think that there are forces on the ladder causing it to shorten.

In fact, this brings to mind an example J.S.Bell gives in one of the talks collected in Speakable and unspeakable in quantum mechanics. Consider two spacecraft A and B. The nose of B is attached to the tail of A by a taut string. The two craft then accelerate in tandem, preserving the distance between them. What happens to the string?

[bunny]

[ QUOTE ]
[ QUOTE ]
Lorentz contraction is not a "trick of the light" so to speak. The contraction of the ladder is not due to forces exerted on it

[/ QUOTE ]

Really? The electric field of a charge moving at relativistic velocities gets foreshortened. I'm pretty sure that Lorentz noticed this and then correctly proposed Lorentz contraction as a fix to explain the Michelson-Morley result. This is probably a bit of an oversimplification, but I don't think it's incorrect to think that there are forces on the ladder causing it to shorten.

In fact, this brings to mind an example J.S.Bell gives in one of the talks collected in Speakable and unspeakable in quantum mechanics. Consider two spacecraft A and B. The nose of B is attached to the tail of A by a taut string. The two craft then accelerate in tandem, preserving the distance between them. What happens to the string?

[/ QUOTE ]

They think it remains taught and at the same length. An observer watching them whizz past thinks the string is shorter (and that both spaceships are shorter).

[Borodog]

[ QUOTE ]
Really? The electric field of a charge moving at relativistic velocities gets foreshortened. I'm pretty sure that Lorentz noticed this and then correctly proposed Lorentz contraction as a fix to explain the Michelson-Morley result. This is probably a bit of an oversimplification, but I don't think it's incorrect to think that there are forces on the ladder causing it to shorten.

[/ QUOTE ]

Yes, I think it would be incorrect to view it that way. There are no internal stresses associated with the Lorentz contraction of the ladder in the barn's rest frame. The ladder is not "squunched" by forces exerted on it, so to speak; rather space and time are different in different inertial frames. Intervals of time, lengths of objects, and measures of angles all change depending on which frame you are in. Consider the barn from the ladder's frame. It is clear that moving the ladder near the speed of light cannot exert forces on the barn to make it contract, can it?

[gumpzilla]

Well, what do you think of the spaceships and string example?

[Borodog]

[ QUOTE ]
Well, what do you think of the spaceships and string example?

[/ QUOTE ]

Bunny answered you correctly there. Because the ships accelerate in lockstep, they are motionless with respect to each other, and do not view any change in the distance between the ships, and the string will remain intact (although if the acceleration is high enough the string may snap due to its own inertia).

Since "Does the string snap?" is a Lorentz invariant question, it either does or does not, regardless of frame, it cannot snap in the frame of any observer. The entire ship-string-ship system will Lorentz contract in the direction of motion.

&gt;&gt;====&gt;&gt;----&gt;&gt;====&gt;&gt; becomes &gt;==&gt;--&gt;==&gt;

[gumpzilla]

[ QUOTE ]

Bunny answered you correctly there. Because the ships accelerate in lockstep, they are motionless with respect to each other

[/ QUOTE ]

Ah, but in which frame? You're suggesting it is the frame of the ships. I say it is the frame of the Earthbound observer. Keep in mind that the frame of the spaceships is accelerating, and it's going to be hard to apply special relativistic precepts in that case unless you're quite careful.

Because the string should be trying to Lorentz contract, it being constrained to remain the same length keeps it from doing so and puts it under stress. So it snaps, eventually. And you're right, it does so in both frames; in the rocket's frame, the rocket in front is seen to be pulling away and stretching the string, if we are to believe Bell. Sorry about the argument from authority, but I'm feeling a little too lazy to actually try doing the Lorentz transforms here at the moment.

[Borodog]

Oh, no, I'm not going to argue. I just assumed that the ships were trying to stay the same distance apart in their frame. The other interpretation makes more sense; if the two ships begin to accelerate at the same rate simultaneously from the frame in which they are initially at rest, you are absolutely correct. They will stay the same distance apart in that frame and the string will snap. This is clearly the better interpretation of what you wrote.

P.S. And I'm not going to argue with J.S. Bell. /images/graemlins/wink.gif

[bunny]

[ QUOTE ]
Oh, no, I'm not going to argue. I just assumed that the ships were trying to stay the same distance apart in their frame. The other interpretation makes more sense; if the two ships begin to accelerate at the same rate simultaneously from the frame in which they are initially at rest, you are absolutely correct. They will stay the same distance apart in that frame and the string will snap. This is clearly the better interpretation of what you wrote.

P.S. And I'm not going to argue with J.S. Bell. /images/graemlins/wink.gif

[/ QUOTE ]

ditto - I misunderstood your scenario /images/graemlins/frown.gif

[PokerPadawan]

OK, I slept on it, let my brain process everything everyone is trying to say, and tried to figure out where this train derailed.

First, Borodog, if I've insulted you, I'm sorry. I honestly am not trying to sound like an "insulting jerk". Maybe I should've used smileys. In any case, I thought your comments about my future failure as a scientist were out of line. None of my research has anything to do with the pole/barn paradox, and the problem I have conceptually (explained below) in no way affects my ability to solve problems.

Second, the original point I was trying to make is that I believe this problem has a preferred frame of reference. This is debatable endlessly. I agree that SR says that we shouldn't prefer one, but I also contend that this problem can be thought about in different ways and still arrive at the same answer. I see now I have an inherent bias toward the stationary pole frame. I could argue that you can do this because the pole was initially at reast and then accelerated, allowing us to distinguish between the two frames. That works in this case.

If, however, you changed the problem to be in vacuum with the 'pole' and 'barn' already in motion and just passing by each other, you couldn't distinguish the frames. I agree with this.

I'm not sure at what point I picked up this sort of observer's bias, but I agree that there is no physical reason to prefer one frame over another, just that it makes things easier sometimes. Please understand that when I say preferred, I mean lessen the workload on scientists, not that the physics are correct only in that frame. I think my years of astrophysics, where things are much more applied, has given me a knee-jerk applied reasoning about things, whereas I used to have a more conceptual, theoretical reasoning.

I hope you all can forgive my blindness to my bias. Wow, I can't believe how it distorted how I perceived your arguments. Pretty scary stuff. In my defense, though, I haven't even thought about special relativity since I was a second-year undergrad. My other relativity classes were all general relativity, which I'm pretty sure I understand a bit better.

[Borodog]

[ QUOTE ]
I thought your comments about my future failure as a scientist were out of line.

[/ QUOTE ]

I think the bulk of your behavior in this thread has been out of line. I couldn't care less if you were "blind to your bias". All physicists occasionally make misinterpretations and mistakes (see just a few posts above where *I* assumed the wrong frame to answer a question; I immediately recognized it and didn't try to insult my way out of it).

What I have a problem with is things like this:

"There is a basic lack of deeper understanding of physics here, which I can't remedy apparently. Think whatever the hell you want . . . I just can't fight your dogma." (in response to me)

"'Because I can't understand why I'm wrong, and I won't open my mind to your explanation?' FYP"

"I believe you are being too arrogant in your definition of reality. You are misapplying the principle of no preferred frame to this problem."

"Now, any scientist worth his salt . . . " (implying I am not worth my salt)

"But no one who isn't argumentative . . . " (implying that I am just being argumentative)

" . . . You just can't seem to get it. You keep making irrelevant statements, repeating the same misapplied generalities, and being generally mocking in your tone, as if you are hoping to prove that you are right and that I'm a moron for not understanding basic relativity. You remind me of the engineers who used to take my upper-level physics classes for fun. They would mock the teacher about some inane detail and totally miss the point, such as mockingly pointing out that the prof missed a subscript somewhere. Or conversely they would get into philosophical discussions in the middle of class and not shut up about it until class had ended and the prof had gotten nothing done. They annoyed the crap out of us physics students, who needed to learn the stuff to move on to the next class.

If you think you know physics so well, why did you quit doing astrophysics?"

In short, you have been an insulting jerk.

FURTHERMORE, I suggest you really sit down and reread your special relativity texts, because dude, some of the stuff you have said in this thread is profoundly wrong. It doesn't have to do with "preferred frame bias".

These:

"And of course you shouldn't say that the pole is entirely in the barn, because it never is."

"That's just because the only information about the pole they can receive is the light from it. That doesn't mean it really was inside the barn. The whole point of this aspect of the paradox is that information that an observer sees is tainted by the fact that light can only move at a fixed, finite velocity."

"The pole was never in the barn because it was never compressed for real, just *visually* length contracted."

"Length contraction is purely a conceptual tool that helps humans do these sorts of tranformations in their heads."

"I have no confusion -- the issue is simple if you just draw it on a space-time diagram. Your quote in bold is very misleading, since it is ignoring those very same simultaneity issues that cause this effect."

"Now, any scientist worth his/her salt would say, "OK, I know that pole was moving very nearly at c, so I should do an inverse Lorentz tranformation to figure out the exact sequence of events." After doing this, they would find that the doors didn't close simutaneously. Why would the scientist do that? Because they would know that relativistic travel distorts things."

In fact, the entirety of Post #4734481.

"Of course contraction is real, but it is apparent, not intrinsic. The problem is, we can only get information from objects at lightspeed, so we have no way of not seeing the contraction. I think basic textbook relativity must encourage overly simplistic thinking."

are all catastrophically wrong in their underlying interpretations of the fundamental implications of special relativity, the Lorentz transformation, and the relativity of simultaneity.

Now, having said what I feel I had to say, I make mistakes all the time, and am often an insulting jerk. So I hope there are no hard feelings. Good luck on your dissertation. I am sure you will have a long and successful career.

[PokerPadawan]

The amount of work that you put into this post, soley to disparage me, is frankly frightening. I've already admitted that I was wrong, and I know why. This verbal teabagging is just immature and unnecessary.

I understand relatively as deeply as anyone who has a physics degree, but I never thought it was that big of a deal. It's just another model for how the world works. I was just stuck in a dead-end line of thinking about this particular problem. I had never thought about this until this topic came up, but the idea that SR can't exert a force started making me think that the pole can't change length. The problem is I forgot that length is a largely irrelevant quantity. I still think it's interesting that no force can arise due to SR, but I can't think of a way of determining that the pole is not being subjected to a force. Even the internal energy is distorted due to time dilation, I bet.

[Borodog]

[ QUOTE ]
The amount of work that you put into this post, soley to disparage me, is frankly frightening. I've already admitted that I was wrong, and I know why. This verbal teabagging is just immature and unnecessary.

[/ QUOTE ]

Pot, kettle. Perhaps you should read your quotes again.

[PokerPadawan]

Let me translate, since you seem to think everything is directed at you.

"There is a basic lack of deeper understanding of physics
here, which I can't remedy apparently. Think whatever the hell you want . . . I just can't fight your dogma."

I'm giving up in desperation. This has nothing to do with you personally. Your is plural.

"'Because I can't understand why I'm wrong, and I won't open my mind to your explanation?' FYP"

OK, that was mean.

"I believe you are being too arrogant in your definition of reality. You are misapplying the principle of no preferred frame to this problem."

You can be too arrogant about something. Like thinking that all life in the universe is carbon-based. Does that make this an insult? No, of course not.

"Now, any scientist worth his salt . . . " (implying I am not worth my salt)

No, you are egotistically thinking I'm referring to you.

'"But no one who isn't argumentative . . . " (implying that I am just being argumentative)'

Why is being argumentative an insult?

" . . . You just can't seem to get it. You keep making irrelevant statements, repeating the same misapplied generalities, and being generally mocking in your tone, as if you are hoping to prove that you are right and that I'm a moron for not understanding basic relativity. You remind me of the engineers who used to take my upper-level physics classes for fun. They would mock the teacher about some inane detail and totally miss the point, such as mockingly pointing out that the prof missed a subscript somewhere. Or conversely they would get into philosophical discussions in the middle of class and not shut up about it until class had ended and the prof had gotten nothing done. They annoyed the crap out of us physics students, who needed to learn the stuff to move on to the next class. "

I'm explaining why you're basically hurting my feelings, and you insensitively and egotistically think I'm insulting you.

"If you think you know physics so well, why did you quit doing astrophysics?"

An honest question. You seem to enjoy arguing about science on the forum, so it seems you liked it. Most people I know who quit science didn't like it.

"In short, you have been an insulting jerk."

Only if you are so self-centered that you interpret every little statement like this to be about you. You are borderline paranoid. Seriously.

[ QUOTE ]
Now, having said what I feel I had to say, I make mistakes all the time, and am often an insulting jerk. So I hope there are no hard feelings. Good luck on your dissertation. I am sure you will have a long and successful career.

[/ QUOTE ]

Is this a joke? You write a post, of which 90% is directly insulting to me, then you pretend to be all nicey nice? LMFAO.

Time for me to get back to spending your tax dollars.

[Borodog]

Grow up.

[Gobgogbog]

You aren't exactly exhibiting the most grown up behavior here either, Borodogo /images/graemlins/frown.gif This has been a really disappointing thread to read, but I've read it anyway because in between the bickering is some pretty neat stuff for someone who hasn't done any relativity

[Matt R.]

[ QUOTE ]
You aren't exactly exhibiting the most grown up behavior here either, Borodogo /images/graemlins/frown.gif This has been a really disappointing thread to read, but I've read it anyway because in between the bickering is some pretty neat stuff for someone who hasn't done any relativity

[/ QUOTE ]

FWIW Borodog did not start bickering until he was insulted numerous times. He clearly felt the need to defend himself (especially because he was right).

[Gobgogbog]

[ QUOTE ]
[ QUOTE ]
You aren't exactly exhibiting the most grown up behavior here either, Borodogo /images/graemlins/frown.gif This has been a really disappointing thread to read, but I've read it anyway because in between the bickering is some pretty neat stuff for someone who hasn't done any relativity

[/ QUOTE ]

FWIW Borodog did not start bickering until he was insulted numerous times. He clearly felt the need to defend himself (especially because he was right).

[/ QUOTE ]

That's why I didn't mention that it was bothering me until it continued so long :/

[Sharkey]

Here is a suggested change to the setup:

When a predetermined part of the pole reaches the midpoint of the barn, a device at that location sends two radio signals in opposite directions parallel to the path of the pole. The signals each go to a mechanism at either end of the barn that immediately shuts the door.

Since the speed of radio signals is the same for all observers, there is no disagreement about the doors closing together.

[bunny]

[ QUOTE ]
Here is a suggested change to the setup:

When a predetermined part of the pole reaches the midpoint of the barn, a device at that location is triggered to send two radio signals in opposite directions parallel to the path of the pole. The signals each go to a mechanism on either end of the barn that immediately shuts the door.

Since the speed of radio signals is the same for all observers, there is no disagreement about the doors closing together.

[/ QUOTE ]

You are right that all observers measure the speed of radio signals as the same - but the same speed relative to their frame of reference.

For instance, from outside the barn, I see the pole-vaulter running at .9c and the radio wave propagating down the pole at c and racing away from him at c. So from my perspective the front tip of his pole is only just behind the radio wave. In contrast, the rear of his pole catches it very fast as the distance between them is decreasing at a rate of 1.9c. The barn is stationary relative to me and I see the wave take equally long to reach both ends of the barn.

His perspective is different though. He sees a radio wave expanding away from him at c and propagating along the pole at c. However, the barn is racing towards him at .9c. This means the gap between radio wave and barn in front of him is closing at 1.9c and the gap between the radio wave and the back door is closing at only 0.1c.

In other words, he observes the radio wave hit the front door before it hits the back door.

[Sharkey]

That sounds right.

How about, instead of two radio signals, there is an actual physical mechanism attached to the doors. When the front of the pole passes the midpoint of the barn, it pushes a lever connected to both doors.

How would relativity produce an asymmetry in this case?

[TomCollins]

[ QUOTE ]
That sounds right.

How about, instead of two radio signals, there is an actual physical mechanism attached to the doors. When the front of the pole passes the midpoint of the barn, it pushes a lever connected to both doors.

How would relativity produce an asymmetry in this case?

[/ QUOTE ]

If you can figure out how to make a physical entity move faster than the speed of light, a Nobel Prize awaits you!

Good luck sir!

[Sharkey]

If I read the problem correctly, the physical device need only work faster than the pole.

[bunny]

[ QUOTE ]
If I read the problem correctly, the physical device need only work faster than the pole.

[/ QUOTE ]

Imagine two bullets are fired, say at the speed .99c. From outside - no problem they reach the barn doors simultaneously and the doors close at the same time.

From the runners' perspective? The forward bullet is travelling at .09c and the barn is racing towards us at .9c (they are closing at .99c). How about the bullet travelling backwards though? If the world was non-relativistic it would be racing behind us at 1.89c. We know nothing travels faster than light though, right? The lorentz transformation gives an answer - we will see it receeding at .999c or something. The rear of the barn is also receeding at .9c so they are closing at .099c.

Thus, from the runner's perspective the front bullet will hit the barn before the back bullet does.

[Sharkey]

[ QUOTE ]
Imagine two bullets are fired, say at the speed .99c. From outside - no problem they reach the barn doors simultaneously and the doors close at the same time.

From the runners' perspective? The forward bullet is travelling at .09c and the barn is racing towards us at .9c (they are closing at .99c). How about the bullet travelling backwards though? If the world was non-relativistic it would be racing behind us at 1.89c. We know nothing travels faster than light though, right? The lorentz transformation gives an answer - we will see it receeding at .999c or something. The rear of the barn is also receeding at .9c so they are closing at .099c.

Thus, from the runner's perspective the front bullet will hit the barn before the back bullet does.

[/ QUOTE ]

There’s a physical mechanism directly connecting a lever at the center of the barn to both of the doors. When the pole passes by, it pushes the lever.

What would account for a difference in timing under those circumstances?

[bunny]

[ QUOTE ]
There’s a physical mechanism directly connecting a lever at the center of the barn to both of the doors. When the pole passes by, it pushes the lever.

What would account for a difference in timing under those circumstances?

[/ QUOTE ]

When you push one end of an object - like the lever in your example, the other end doesnt move immediately. The molecules you move at your end bump into the molecules next to them, they bump into the next lot, etc, etc...imagine a line of dominoes knocking each other over.

Basically a wave propagates down the lever at a very fast (but slower than lightspeed) velocity. These waves will travel at different speeds and the forwards one will hit the barn first.

[Sharkey]

[ QUOTE ]
When you push one end of an object - like the lever in your example, the other end doesnt move immediately. The molecules you move at your end bump into the molecules next to them, they bump into the next lot, etc, etc...imagine a line of dominoes knocking each other over.

Basically a wave propagates down the lever at a very fast (but slower than lightspeed) velocity. These waves will travel at different speeds and the forwards one will hit the barn first.

[/ QUOTE ]

What would account for the difference in speeds?

[bunny]

I think it's due to the little "bumps" between molecules all being subjected to their own relativistic effects (ie ultimately, it is electromagnetic interactions - billions of them that tell the far end of the lever to move. So it is really just "adding up" a number of separate events similar to your radio wave example).

I have to confess this thread has got close to exhausting my knowledge of special relativity though - it's been over 10 years since my last physics course! /images/graemlins/tongue.gif

Suffice it to say - I know there is an answer to this but I'm afraid I cant remember it in anything but the vaguest way.

[Sharkey]

Thanks for your answers. It’s a tough subject, no doubt.

Incidentally, the mechanism I’m referring to is made of the famous “rigid rods”.

[Mik1w]

Yep.. the second door closes and opens before the first one does as observed by the man with the pole... the events are at different spacial coordinates and not simultaneous, this can be shown using the lorentz transformations.

another itneresting one is this: you have a brick of length L and you push it along a surface with a speed v. The surface then has a rectangular hole with length L-a. A stationary observer sees the the brick is contracted and can fit in the hole, but the brick sees that the hole is even shorter and so it won't fall in. Does the brick fall in?

[Sharkey]

[ QUOTE ]
Yep.. the second door closes and opens before the first one does as observed by the man with the pole... the events are at different spacial coordinates and not simultaneous, this can be shown using the lorentz transformations.

[/ QUOTE ]

Of course the events happen separately according to their spacetime coordinates. But whether that system of representing reality can be made consistent with other known knowns is the issue.

[oneeye13]

i did the experiment

it fit

[bunny]

[ QUOTE ]
[ QUOTE ]
When you push one end of an object - like the lever in your example, the other end doesnt move immediately. The molecules you move at your end bump into the molecules next to them, they bump into the next lot, etc, etc...imagine a line of dominoes knocking each other over.

Basically a wave propagates down the lever at a very fast (but slower than lightspeed) velocity. These waves will travel at different speeds and the forwards one will hit the barn first.

[/ QUOTE ]

What would account for the difference in speeds?

[/ QUOTE ]

When you move an object (like a rigid rod) the whole thing doesnt move as one. You push your end and the molecules near you have to bump into the molecules next to them, who have to bump into the next lot, etc etc until the molecules on the far end get bumped and the whole thing has moved.

Imagining two rigid rods moving away to operate the door mechanism you would observe the one in front of you move as per usual, the rod pointing behind you though would move much slower. This is because each of the little interactions is slower in your reference frame than in the frame of the barn.

Wiggling one end of an object doesnt cause instantaneous wiggling at the other end - the message to wiggle can't propagate any faster than the speed of light (same as everything else).

[Sharkey]

Okay. The "signaler" at the center of the barn is a very massive object that vibrates when activated. The device at either barn door senses this "tidal" stress and shuts the door.

[Borodog]

[ QUOTE ]
Okay. The "signaler" at the center of the barn is a very massive object that vibrates when activated. The device at either barn door senses this "tidal" stress and shuts the door.

[/ QUOTE ]

Gravity doesn't travel faster than the speed of light either.

[Sharkey]

[ QUOTE ]
[ QUOTE ]
Okay. The "signaler" at the center of the barn is a very massive object that vibrates when activated. The device at either barn door senses this "tidal" stress and shuts the door.

[/ QUOTE ]

Gravity doesn't travel faster than the speed of light either.

[/ QUOTE ]

So, then how does it cross the event horizon?

[Borodog]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
Okay. The "signaler" at the center of the barn is a very massive object that vibrates when activated. The device at either barn door senses this "tidal" stress and shuts the door.

[/ QUOTE ]

Gravity doesn't travel faster than the speed of light either.

[/ QUOTE ]

So, then how does it cross the event horizon?

[/ QUOTE ]

It doesn't. For the outside observer, mass falling into a black hole never actually crosses the event horizon.

[Sharkey]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
Okay. The "signaler" at the center of the barn is a very massive object that vibrates when activated. The device at either barn door senses this "tidal" stress and shuts the door.

[/ QUOTE ]

Gravity doesn't travel faster than the speed of light either.

[/ QUOTE ]

So, then how does it cross the event horizon?

[/ QUOTE ]

It doesn't. For the outside observer, mass falling into a black hole never actually crosses the event horizon.

[/ QUOTE ]

Well, then it must at least be very attenuated from causes like those responsible for the red shift of light under the same circumstances. This would follow from a finite propagation speed, if I recall my spacetime correctly.

[bunny]

[ QUOTE ]
Well, then it must at least be very attenuated from causes like those responsible for the red shift of light under the same circumstances. This would follow from a finite propagation speed, if I recall my spacetime correctly.

[/ QUOTE ]
I dont understand what you mean by this. Gravity is also bound to travel slower than light - so the same arguments apply in this case also. What do you mean by attenuated?

[Sharkey]

[ QUOTE ]
[ QUOTE ]
Well, then it must at least be very attenuated from causes like those responsible for the red shift of light under the same circumstances. This would follow from a finite propagation speed, if I recall my spacetime correctly.

[/ QUOTE ]
I dont understand what you mean by this. Gravity is also bound to travel slower than light - so the same arguments apply in this case also. What do you mean by attenuated?

[/ QUOTE ]

I’m referring to the dilation of space in the gravity well of a black hole, which makes electric field strength appear weaker to a distant observer.

The same effect should apply.