I am not against the mainstream beliefs (I support them). I am starting this thread because several mainstream supporters seem to be claiming that a moving object does not contract in the direction of motion. I believe this actually goes against mainstream beliefs.
So the point of this thread is: For mainstream supporters on this site to come to a consensus on the predictions of SR regarding length contraction so that there is no confusion in the future. (The discussion may also serve as a learning tool for those watching that are still having trouble with relativity.)
As such, please do not post in this thread unless you feel you support special relativity.
I have already been accused of "strawman arguements" by clj4. So let me show why I feel there is non consensus.
Tim Thompson wrote:
As for the misleading part, in real, 3D space, there is never a contraction of any real 3D object, nor has the mainstream ever held that there was. The contraction you are thinking of is a teaching tool meant to simplify the problem and reveal fundamental physics, and is valid in one and only one dimension. (link to post)
When discussing the predictions according to an observer moving relative to a sub, MacM stated that this observer would see the sub contracted and therefore denser.
No, this is not correct. Objects moving at very high speeds do not contract
and then contradicted himself in the same post saying
...they appear contracted when viewed from other frames of reference...
(link to post)
To help make this discussion on the predictions straight forward, let me attempt to focus the discussion as much as possible.
We are discussing: does a moving object contract in the direction of motion according to special relativity?
And here are three comments on the matter in case there are questions of ambiguity:
1] By definition an object is not moving in its rest frame. So of course an observer in its rest frame does not see it contracted, because it is not a moving object in this frame.
2] The "terrell rotation" is what "appears" to an observer in the direct sense of what he sees. In other words, before correcting for the fact that light from different parts of the object take different amounts of time to reach the observer. So this is just an optical effect, and we need to account for the finite speed of light to obtain the object's orientation and size in this frame.
3] A well known relativity thought experiment to help us focus this discussion:
Let's take two small rockets (I'll just treat them as points, if you really want to be picky the points I am referring to are their center of masses) and an observer. All three are initially at rest with respect to each other.
Initially have the rockets laying horizontally some distance d apart. To be even more unambiguous, have the observer set up a coordinate system according to Einsteins conventions. Now, program the rockets to launch simultaneously according to the observer and use constant thrust for a set amount of time. Will the distance between the rockets decrease according to the observer? Do the calculations, blah blah, and the answer is no.
Okay, now let's take this farther. Put an elastic string between the two rockets (initially straight / no slack but also no tension). Give them extra strong thrusters so that they can maintain their correct path no matter what (basically, make sure the string's effect on the rockets' trajectory is negligible). Same thing, launch simultaneously. Now again the distance between the rockets does not change according to the observer. But, will there be tension in the string? Do the calculations, blah blah, and the answer is yes.
At what length would there be no tension in the string? It's at the normal length contracted distance.
In short, if an object WASN'T length contracted in the direction of motion, there would be tension trying to bring it into the now shorter equilibrium length.
Some (not all) mainstream followers at this site seem to be claiming otherwise.
Maybe we are actually in agreement but using different meanings in our phrases (which is fine, I would just like to make sure this is the case and then we can be aware of it).
Comments are appreciated.