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Special relativity (SR) theory has a part called length contraction. There is evidence for it on subatomic scale in particle accelerators, but none that I know of on large scale.(Incoming muons having a longer than expected "lifespan" does not make Earth's atmosphere thinner (contracted), except "for a muon," not actually thinner)SR theorists claim that from a frame of reference flying by Earth at near light speed ('c') Earth's diameter as measured in the direction of the fly-by would be contracted, making Earth a very oblate spheroid rather than the near sphere established by Earth science. Further, they claim that the effect is not just a distortion (appearance only) but that Earth is in fact flattened (like the subatomic particles) "for that frame of reference" and that "there is no preferred frame of reference," so that measurement (flattened shape of earth) is "equally valid."What say you SR experts here?
It actually is defined just the way you doubt As belonging to your 'local clock and ruler'. And that local clock will always fit that local ruler just the same, and the definer of how that come to be is 'c', lights speed in a vacuum. The question then becomes if this contraction is a illusion or a reality. As far as I can see it's a reality, not a illusion. The contraction logically follows from the stipulation that lights speed in a vacuum constantly is the same, no matter from where you measure it. If you assume that 'time' is a illusion you then will have to do the same with 'distance' as they are complementary phenomena, meaning that what A measure for B may be a slower 'time', but from B:s side his time will be the same as always although the distance measured is 'contracted'. So to invalidate it one will have to redefine 'c' as a variable instead of a constant.
From the rest frame of the ship it is completely valid. From the lab on earth we can predict with accuracy what the ship would observe and it matches what the ship's crew do observe.
What I am still confused about however is the difference between the phrases (edited)... "for the ship flying by Earth” (its diameter is contracted) and its actual diameter(s) (polar a bit shorter than equatorial) as well known and documented by Earth science.
1. Definition of lenght between two points of an object: measure the simultaneous position of the two points and make the difference.2. In SR simultaneity is frame-dependent (= if two spatially separated events are simultaneous in a frame, they are not in a frame which is moving with respect to the first).
Does “valid” for the ship mean that ‘flattened’ ( having a contracted diameter) is a valid description of Earth? How can that be?
A ship traveling at near ‘c’ velocity from here to there must, therefore take longer than 4.37 years to get there, even though the onboard clock will have slowed down and recorded much less than 4 years passing. Yet Earth will have orbited the Sun (the "year" standard) much more than 4 times during the ship’s journey to AC. So, even though “for the ship” much less than 4 years will have passed, the distance between Earth and AC will not have contracted to way less than 4 light years. The ship’s journey obviously will not make Earth and AC move closer together.
Do you think there are no natural objects with intrinsic properties or distances between established by gravity as they were formed in space? All the cosmos depends on how it is observed? Is this not relativity's version of classical subjective idealism, with 'frame of reference' as the abstract, virtual "subject."
If we imagine the ship travelling at 86.6% the speed of light, that speed conveniently slows its clocks to half the normal speed and contracts the ship to half its normal length
Lightarrow said:Quote1. Definition of lenght between two points of an object: measure the simultaneous position of the two points and make the difference.2. In SR simultaneity is frame-dependent (= if two spatially separated events are simultaneous in a frame, they are not in a frame which is moving with respect to the first).Regarding #1: This would seem to yield the familiar earth science measurements of earth, say as from in orbit, at rest with Earth.Regarding #2: I don’t understand how the relativity of simultaneity addresses the question of a length contracted Earth diameter or my statement, “Surely SR's length contraction theory is not claiming that earth's atmosphere depth and diameter varies with how they are measured.”
Is there any empirical evidence for large scale length contraction?
...the ship is a solid object. It would require a tremendous force to squeeze the ship to half its normal length, (and it would be crushed in the process), and I am sure that "length contraction" is not claiming to be such a force.
Likewise for the astronomically verified distance between Earth and AC. A ship observing the distance to have contracted is not the same as the two bodies actually becoming closer together in space.
Einstein appears to offer a spacetime in which the contractions are not real - things appear to contract, but they're really just reorienting themselves in spacetime such that they appear shortened from other frames because part of their length is taking up part of the time dimension.... with Einstein's theory there is no real contraction at all, but just the appearance of contraction when viewed from other frames.
Without a preferred frame, the distances between things can be measured accurately within the frame in which they're stationary, and that would arguably be the truest measurement.
If you are still with respect to Earth, every Earth's dimension has a value, in your frame of reference; if you are moving with resperct to Earth, those dimensions are different, as measured in that new frame of reference (because of #).In relativity you *cannot* say: "the lenght is 2 metres", you have to say: "the lenght is 2 metres as measured in this specific frame of reference".
But lightarrow said:QuoteIf you are still with respect to Earth, every Earth's dimension has a value, in your frame of reference; if you are moving with resperct to Earth, those dimensions are different, as measured in that new frame of reference (because of #).In relativity you *cannot* say: "the lenght is 2 metres", you have to say: "the lenght is 2 metres as measured in this specific frame of reference".Does this claim that Earth changes shape as it is measured from different frames of reference? This, of course, is impossible and has never been empirically observed. So the claim seems to be that there are no actual objects with intrinsic properties (or distances between them) independent of how they are observed/measured?
Here is another “reality check” against large scale length contraction:Say an alien probe is discovered heading toward Earth at a significant fraction of light speed. From Earth’s frame it is measured to be ten meters long, length contracted because of its velocity relative to earth. It is decided to go out and intercept/capture it in one of our very high speed space shuttles (of the future.) Our shuttle has a ten meter cargo bay. Will the probe fit into the bay?... A very practical test of “actual length” vs “contracted length.”The answer is “no” because the probe’s “actual length” must be longer than its “contracted length” for it to appear as ten meters long from earth’s frame in this case.