Is a length contraction just a visual thing?

[exchemist]

SCNR means "sorry, could not resist".

Aha, thanks. If I'd known what that stood for, I'd have got your meaning first time

 

[Billy T]

... In the 45 minutes or so of nice classical music and particle trails, you can see trails that can't have been made by particles from the sample. {pitchblende} ...

Yes some are linear lines of condensed vapor, which do NOT extend back thru the pitchblende, so did not come directly from it. Possibly they were made by gamma rays which are also emitted by pitchblende. The gamma ray would not leave a condensation track so its path from the pitchblende is not seen. If it interacts with mater, perhaps by Compton scattering, the recoil energy left in the scattering particle, for example a previously bound election, can be ejected only in the same plane as the initial gamma ray and the slightly lower energy scattered gamma ray. The path of that scattered charged particle will (or can) make a condensation trail that seem to start from some point in space, not the pitchblende location.

Other trails not pointing back at the pitchblende do seem to be a bend of the alpha particle tracks. They most probably result from a near nuclear collision of the alpha with some air or vapor molecule in the chamber. Most commonly, I think, are the scattered alpha particle, if the bend is near the end of the linear track back to the pitchblende as the alpha has lost most of its energy and is easy to scatter thru a substantial angle. Probably there are some tracks not extending back thru the pitchblende that have their "bends" close to the pitchblende that are also results of collisions with more energetic alpha that break up the nucleus of a gas atom. I did not see any, but photo graphs may show a single track that splits at the bend into two or more tracks.

 

[arfa brane]

Yes some are linear lines of condensed vapor, which do NOT extend back thru the pitchblende, so did not come directly from it. Possibly they were made by gamma rays which are also emitted by pitchblende.

Possibly, but it is hard to reconcile the tracks that appear to move towards the sample from outside the chamber, with particles emitted by the sample.

And it's harder to reconcile the tracks that appear when there is no sample present, as in the first DIY video.

Further, there is an online lecture somewhere (I'll try to relocate it), in which the lecturer demonstrates the presence of muons with a glass, some brandy, some dry ice and a torch. There are plenty of references online about how to make your own cloud chamber (cooling is required, but need not be dry ice which is expensive and hard to find these days), and what kinds of tracks muons make (some are linear, some are curled).

 

[arfa brane]

I should correct something. Muons make linear tracks, the curly tracks are made by electrons or positrons.

If you build a could chamber as in the two examples, it will detect muons moving roughly parallel to the earth's surface. This is why muon tracks are relatively rare events in either case.

 

[DaveC426913]

You are asking whether this contraction is real or just a kind of visual illusion, in effect. The contraction that you measure for moving objects is the same however you measure it. The only thing that matters is your frame of reference as an observer - or, to put it another way, the relative speed between you and the object being measured. If you leave the object alone and just move yourself, you'll still see the length contraction of the object.

I think most physicists would be inclined to say that the length contraction of the object is a real effect.

There is a thought experiment that puts this to the test.
The gist involves a 20 foot pole (or ladder) traveling at relativistic velocities tossed into a barn (or garage) that is only 10 feet long. The queston is essentially, will the pole fit in the barn, even for a brief moment?

The answer strikes at the heart of what it means for space-separated events to have relativity of simultaneity.

https://en.wikipedia.org/wiki/Ladder_paradox

 

[ajanta]

This question was directly answered in post #62 where calculations with the Lorentz transform demonstrate that the definition of length, the definition of simultaneity, the definition of co-moving require that length can actually change when you change which inertial motion you use as your standard for deciding what is the meaning of "at rest" and "simultaneous."

Importantly, length contraction has nothing to do with issues of perspective and vision. It's about definitions and standards.

The question in the OP was about the physics described by the Lorentz transform. Thus it can be answered without reference to the actual behavior of the universe -- we only need the model of the universe. Your assertions about perspective is without basis, does not address the math of perspective calculations, and does not address the definition:

Length of an object in inertial motion is the absolute difference in position between the two endpoints at the same time.​

The physical length will be different as measured by different observers at rest and not at rest with respect to the object.

The measurement technique - sight, etc - does not matter. The observer can use whatever measurement equipment and methods they regard as best.

Which one of those lengths do you wish to label the "actual length"?

A GPS technology in rocket A can measure the length of that rocket. Suppose there is a nuclear bomb in the rocket and if the GPS technology measure any variation of length of rocket then it will trigger the bomb.

Now rocket A and Another rocket B it moving parallel at 0.8c and an observer X on earth and two observes in rocket A and B are observing each other. Simply rocket A will distroy by explosion for which observer's observation ?

 

[DaveC426913]

A GPS technology in rocket A can measure the length of that rocket. Suppose there is a nuclear bomb in the rocket and if the GPS technology measure any variation of length of rocket then it will trigger the bomb.

Now rocket A and Another rocket B it moving parallel at 0.8c and an observer X on earth and two observes in rocket A and B are observing each other. Simply rocket A will distroy by explosion for which observer's observation ?

The GPS technology is subject to remote observation, just like anything else. So, rocket A is doing the detecting, and has the trigger; it will trigger the bomb as it sees fit.

There is nothing wrong with different observers seeing different events. They know that the remote events are modified by relativity, and will account for that in their observations.

 

[ajanta]

The GPS technology is subject to remote observation, just like anything else. So, rocket A is doing the detecting, and has the trigger; it will trigger the bomb as it sees fit.

There is nothing wrong with different observers seeing different events. They know that the remote events are modified by relativity, and will account for that in their observations.

Yes it was my mistake about GPS. If it is only a technology in A rocket alone then what will be about all observers observation
?

 

[DaveC426913]

If it is only a technology in A rocket alone then what will be about all observers observation
?

I'm sorry, I'm not sure what you're asking.

There is nothing wrong with different observers seeing different events. They know that the remote events are modified by relativity, and will account for that in their observations.

 

[The God]

....They know that the remote events are modified by relativity.......

Events cannot be modified by any theory..

 

[exchemist]

Events cannot be modified by any theory..

Trivially true, but from the context that is obviously not what he meant.

 

[The God]

Trivially true, but from the context that is obviously not what he meant.

You mean he was referring to "relativity of simultaneity"?

 

[exchemist]

You mean he was referring to "relativity of simultaneity"?

Well in a more general sense, that the way one perceives a remote event is potentially different from the way an observer at and moving with the event perceives it, due the effects of the physical phenomena that we generally call for convenience "relativity".

 

[The God]

Well in a more general sense, that the way one perceives a remote event is potentially different from the way an observer at and moving with the event perceives it, due the effects of the physical phenomena that we generally call for convenience "relativity".

Good.

 

[ajanta]

I'm sorry, I'm not sure what you're asking.
.

Events cannot be modified by any theory..

Trivially true, but from the context that is obviously not what he meant.

And I'm confused too.

Honestly I was thinking about switching that is interesting to me also.
May be it is not possible but a question....


I mean 2 separate primary(That can produce powerful magnetic field) and secondary coil with armature. The distance between two coils is 1 meter and then primary coil is not able to transfar energy to secondary coil but when length or distance contraction will contract the length or distance into 1cm then,.... Is the primary coil able to transfer energy to secondary coil ?

 

[The God]

And we were stick with twin paradox. In fact we can write a book on various laughter inducing scenarios on length contraction and time dilation.

 

[DaveC426913]

And I'm confused too.

Honestly I was thinking about switching that is interesting to me also.
May be it is not possible but a question....


I mean 2 separate primary(That can produce powerful magnetic field) and secondary coil with armature. The distance between two coils is 1 meter and then primary coil is not able to transfar energy to secondary coil but when length or distance contraction will contract the length or distance into 1cm then,.... Is the primary coil able to transfer energy to secondary coil ?

I'm sorry. I realize English is not your first language, but I can't parse the sentences. In particular, there seems to be some missing verbs and punctuation.
And I have no idea what this has to do with relativistic length contraction.

I'm going to have to bow out, rather than keep asking for clarification.

 

[ajanta]

I'm sorry. I realize English is not your first language, but I can't parse the sentences. In particular, there seems to be some missing verbs and punctuation.
And I have no idea what this has to do with relativistic length contraction.

I'm going to have to bow out, rather than keep asking for clarification.

Hmm ! So I think I asked silly question with silly sentences

 

[The God]

Hmm ! So I think I asked silly question with silly sentences

No, you did not, it was a perfectly valid question. But many a times such questions, which require substantial responses, prompt people to bow out by finding fault in sentences or making irrelevant reference that xyz first language is not English, as if that matters.

Length contraction and time dilation are frame specific scenarios. It has many paradoxes associated with it and creates many non-intuitive situations. What I find most disturbing in SR/GR maths (not that I know much of it) is that in SR division by zero (V = c) is conveniently excluded by saying that a photon cannot have rest frame while in GR division by zero is a big business empire (Black Hole).

PS: By the way do you know that people with 'x' as their first language, can be very poor in sentence writing and general grammar in x if they do not have formal learning of 'x'.

 

[DaveC426913]

Hmm ! So I think I asked silly question with silly sentences

No, I don't think it's a silly question. But I'm not sure. Maybe you could rephrase.

(If Tim would like to think that I am deliberately pretending to not understand that's his problem. If he wants to use it as an opportunity to take shots, that's also his problem.)