Length contraction : Physical or visual?

Length contraction is what is measured. When solar muons have their fixed lifespans in their rest frame, but survive to reach Earth's surface, then Earth's atmosphere *must* be contracted.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ...

Nature does not care about the grief we have when we have to unlearn "crib physics", and retrain our "common sense" on the world of the high speed. She thinks we are food. So since the thinks little of us your question is either:

- nonsense, or

- answers itself.

If light speed is the fastest communications means, like where two ends are to any given observer, what is the difference between "how far apart are the ends, no really, I want to know", "how far apart are the ends visually", and "how far apart or the ends measured to be".

In every case, they must be *measured* to be rest-length / gamma, if rest-lifespan * gamma is observed. You, like the rest of us, will have to fall back on what is logically consistent.

Say I am moving very fast...

You and I agree on *my* speed. You and I agree on the same constant speed of light. So you have to let Nature control what else is seen / measured (which is as close as we can get to "Reality").

I could break out aetherist arguments, and explain how since the size of real objects is maintained by c-moderated forces, requiring 2-way light communications (atomic and molecular bonds). Moving fast, means light has to "run upstream and downstream", which produces length contraction. But then this is a crutch, and aether (even Lorentz aether) does not survive General Relativity, so you'd have to unlearn this crutch too.

[EDIT: "So all agree, the contraction is physical,"

No, it is not "physical", as in "real". It is just what is measured, by any means you might figure to measure it.

"but does this mean? if I am travelling past Earth at .999999% c, will I observe the Earth physically contracted to little more than a vertical line."

A flattened disk or extremely oblate spheroid, yes.

]

[EDIT: "When you say, No, it is not "Physical" are you saying, in the current understanding of the mass of matter that makes the Planet Earth, there is no actual physical / no actual ' Matter ' contraction?"

You keep dancing around trying to get to Truth. Science has no access to Truth, and our sole tool... Measurement, is how we access Reality. All we can know of Reality, is what we can measure. Nature does not want this question answered, which means either it is based on nonsense, or it answers itself with a little thought.

Measurement shows us that every length in the direction of motion is and must be contracted. And yet, they that fly by us, say the exact same thing about us. Physics is the same for both of us, so... is distance / duration any Absolute thing, or is it frame dependent?

You must adjust your journey, if it is taking you places you cannot, will not go...

]

[EDIT: "This question needs answered, the answers everywhere, including wikipedia are grey when considering mass v relative mass etc. You're beginning to sound like a politician who won't give a straight answer."

I have given you the correct answer, however. Maybe I have not been clear enough.

"Question " does matter as we understand it " contract? Yes or No."

We cannot know. Nature does not answer this question. She shows us what is measured. Period.

"PS. With a little thought the question may answer itself, but I am asking for you answer and anyone else's answers and thoughts."

You have mine.

]

It's certainly not visual, since aberration generally makes it *appear* not to have shrunk at all. It is a physical effect. The ruler/rocket is actually measured to be shorter in a frame in which it is in motion.

It's relative. The outside observer sees the contraction and it is physical for him. For the onboard observer, the contraction does not happen to him or his shape but outside objects contract and that's physical for him as well.

Deepest sleep. Also called R.E.M. (rapid eye movement).