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Weirdness

  • Thread starter Thread starter Deleted member 473
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Trev said:
Well, that's confused things no end:frantic:
Not Click, the diagram.
Click to expand...


Sorry! All it shows is that as time advances for the observer, he sees the car from further back in time, not further on in time, in classical mechanics. The light emitted at each instant is slower than the car, and arrives later and later at the observer's eyes.

The low slope of the car line indicates extremely high speed (large distance in small time) but the light rays have a much higher slope. If the car were travelling slowly, its line would be more vertical than the light rays and you would see its travel in the correct sequence.

Whoops! Got the car line wrong! Will re-do! [Done! :oops: ]
 
I shall have to think about this, drag out my undergraduate physics stuff, but this is not in line with my recollection of Special Relativity.
 
Black Hole said:
I shall have to think about this, drag out my undergraduate physics stuff, but this is not in line with my recollection of Special Relativity.
Click to expand...


What is actually seen is a fairly new area of investigation. In fact, Gamov got it wrong in Mr Tompkins. He assumed that the contraction would be visible and obvious, but forgot about the finite speed of light. Attached is a paper on this subject. I don't know if the same has been done for classical mechanics, but clearly some pretty weird stuff is visible there too. It's partly relativistic effects but also the effect that the finite speed of light has on first person observation. Any object speeding past us, even in classical mechanics, will look distorted, just because we see different parts of it from different times in its past.
 

Attachments

You can't believe everything you read on the Internet. All I can say for the moment is "Lorentz Contraction".
 
That's exactly where I was coming from;) I also understood that the mass approached infinity as well.
But I don't understand as well as Dr Hawkins.
 
Trev said:
That's exactly where I was coming from;) I also understood that the mass approached infinity as well.
But I don't understand as well as Dr Hawkins.
Click to expand...


Quite correct. The Lorentz contraction occurs, but it is a funny, two-way thing: each observer appears contracted in the frame of the other when they are in relative motion. However, to deduce that the contraction has happened, you have to do a bit of calculation, because the light from each end of a rod, say, takes time to get to you.

But you actually see the near and far ends of the rod emitted at different times in your frame. This means that you don't actually see the contraction.
 
I think that's a load of bo**ox, but I don't have time to prove it at the moment. At the instant the object passes the observer, its front end and back end are equidistant from the observer, so light time doesn't come into it.
 
So it gets shorter whilst approaching and longer whilst receding? Are we talking red and blue shift here? Or perhaps magenta shift;)
 
I can see the point, the rear of an approaching object has to emit light sooner than the front of it so it will be further away at the time than one length behind the front (by the time the light reaches the front). However, whether that effect counteracts Lorentz contraction I am not sure at the moment, and in any case the SR thought experiments (the only way to do this stuff) "measure" length when the moving object is at closest approach.

The approaching object will be cyan-shifted, and receding it will be magenta-shifted, indeed. By the same argument, when receding it will appear shorter due to the differences in light time, but again that is irrelevant to Lorentz contraction. All that remains is to calculate how much longer an approaching object appears due to the light time, and compare that with the Lorentz contraction to see which is greater. Maybe I'll get around to it later.

None of this affects the order of events observed in a collision.
 
...oh, and there's time dilation to worry about too. The calculation may not be quite as simple as I thought.
 
Black Hole said:
...oh, and there's time dilation to worry about too. The calculation may not be quite as simple as I thought.
Click to expand...

http://www.spacetimetravel.org/filme/stab_s80/stab_s80-ee-640x480.mpg

As the Lorentz contracted object approaches, it appears much longer than its rest length. As it passes, it appears to have its rest mass. A sphere appears as a sphere, always, but rotated. Cubes appear rotated and distorted.

If you are travelling at speed, things behind you appear in front of you. As you approach the speed of light, the whole universe appears as an intense dot ahead of you, radiating at frequencies approaching infinity!

Get out of that! :p
 
Black Hole said:
None of this affects the order of events observed in a collision.
Click to expand...

I never said it did in relativity. It's the perceived order of events that is wrong in classical mechanics. We can calculate back to the real order of events.

Black Hole said:
I think that's a load of bo**ox, but I don't have time to prove it at the moment. At the instant the object passes the observer, its front end and back end are equidistant from the observer, so light time doesn't come into it.
Click to expand...


So where is the middle as it passes you? In your scenario, light from the middle will already have passed you when light from the ends arrives.
 
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