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IAN STINE
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When I accelerate my object it shrinks lengthwise: 1.nose moves back closer to tail OR 2.tail moves forward closer to nose OR 3.both ends move closer to middle OR 4.none of the above ?
This is not true. The shrinking of the object is part of the squashing of space in the direction of motion which allows you to travel large distances in as short a time as you like even though you never exceed the relative speed of light.DrGreg said:Your object doesn't really shrink in any physically measurable sense. From a "static" observer's point of view, his or her calculation of the length has shrunk.
Absolutely incorrect. The phenomena you are talking about (which accounts for the time it takes light to reach the observer) is called the aberration of light. This is a completely different distortion of what you see, and the effect is to make things appear to be stretched out, rotated and far in front of you. See http://www.fourmilab.ch/cship/aberration.html or my simulator at http://www.relspace.astahost.comDrGreg said:The calculation is made from observations and must account for the fact that it takes time for light to travel from the object to the observer.
It is true that the shrinking of the object must be calculated because the aberration of light means that you see something completely different. But this calculation represents where things really are in relationship to you, rather than just what you see. It is the truth behind the illusion. But it is a relative truth because from the objects point of view (to an observer residing on the object) it is you who are squashed not it. This seems like a contradiction but it isn't because of the relativity of simultaneity. Both you and the (observer on the) object "see" (in an interpretive sense) different parts of each other at different times. If there are clocks on the object, which to the (observer on the) object are sychronized, then you "see"DrGreg said:Different observers perform the calculation using different assumptions and so they get different answers.
If, instead, your object remains "static" and the observer accelerates, the observer will still calculate that the length of the object has shrunk, even though nothing has happened to the object at all.
To come back to the original post in this thread, the reason IAN STINE's object shrinks isn't because the object itself has undergone some physical change, it is because the convention for measuring distance differs between the object's rest frame and some external observer. (You can call that "squashing of space" if you like, although I prefer not to.)
DrGreg said:To mitchellmckain:
This is an excellent assumption to make - the basis for all Relativity theory. Under that assumption you can successfully predict the results of any meaningful and relevant experiment you may care to do (in the context of this thread, at least). Nevertheless, it is an assumption and not a fact. (If you believe it is a fact, see this thread: Einstein's Clock Synchronization Convention. It is possible - but painful - to make alternative assumptions and still get the right answer.)
To come back to the original post in this thread, the reason IAN STINE's object shrinks isn't because the object itself has undergone some physical change, it is because the convention for measuring distance differs between the object's rest frame and some external observer. (You can call that "squashing of space" if you like, although I prefer not to.)
I am perhaps guilty of being pedantic in my choice of language over what is "real" or "physical".selfAdjoint said:This argument that Lorentz dilation is just a "convention for measurement" ignores that the muon's relativistically extended lifetime really does permit it to reach the surface and be detected from where it is produced in the upper atmosphere, where as its proper lifetime (which you somehow regard as more real) would have it decay before it had moved a few feet in the Earth frame. Lorentz dilation is real, it is physical and it is different for differently moving observers.
I agree wholeheartedly.selfAdjoint said:You cannot apply your intuitions gained from the slow moving conditions of human life to physics at relativistic speeds.
Actually I wasn't thinking of GR -- my knowledge in that area isn't very deep either.mitchellmckain said:I think I get what you are saying. In fact I think you are approaching this from the standpoint of general relativity as compared to my very exclusively special relativity oriented explanation.
DrGreg said:Actually I wasn't thinking of GR -- my knowledge in that area isn't very deep either.
I was thinking of Lorenz ether theory. In my opinion this isn't a very good theory but, if properly formulated, it isn't actually wrong, in the sense that the results it predicts are identical to those of SR. I believe (correct me if I'm wrong, anybody) you can justify the theory using the mathematics of GR -- you have to use a non-orthogonal coordinate system with a non-diagonal metric tensor.
The point is you can "leisurely walk over" only if you are traveling at the same speed as the object you are measuring. If the object is moving at high speed relative to you, or you are moving at high speed relative to object (which means the same), you cannot measure both ends of the object at the same time yourself -- you cannot be in two places at once -- so you need an assistant to measure the other end. Both of you need to have a way of synchronising your clocks so you can agree what is "at the same time".IAN STINE said:... the "ground state" whereby I leisurely walk over to a circumstance and lazily put my tape measure on things and obtain lengths which I and any bystanders would agree are the "real physical" information about sizes versus the "extreme state" wherein very rapid motion causes optical illusions because different lengths of lines of sight make photons originating from an object's real physical front and real physical rear reach my eye at substantially different times.
Relativistic contraction, also known as Lorentz contraction, occurs when an object moves at a high speed relative to an observer. This causes the object to appear shorter in the direction of motion due to the effects of time dilation.
Yes, relativistic contraction is only significant at speeds close to the speed of light. At slower speeds, the effects of time dilation and length contraction are negligible.
Relativistic contraction is a real phenomenon that has been experimentally observed and verified. It is a fundamental aspect of special relativity and is essential for understanding the behavior of objects at high speeds.
The direction of motion does not affect relativistic contraction. The amount of contraction is solely dependent on the speed of the object relative to the observer. However, the direction of motion does affect the direction in which the object appears shorter.
No, relativistic contraction cannot be reversed. It is a result of the fundamental principles of special relativity and cannot be overcome or reversed by any physical means.