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skepticalbip said:
Loren Pechtel said:
Shadowy Man said:
And I’m saying that’s incorrect physics. Can you give me any reference or physics theorem that supports your conjecture? Can you outline the transformation equations from the moving car frame to the observer’s frame that show that the length of the car will be expanded, in conflict with the standard Lorentz contraction result?

Basically, length contraction is not a Doppler effect it is a special relativistic effect from reference frame transformations.
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While there obviously would be a Lorentz contraction involved in the car that's not what the cartoon shows. That is purely the doppler effect at work--the light turns blue because it's compressed, the light turns red because it's stretched out. The image carried by the light is compressed/stretched the same as the photons themselves.
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That's confusing. Are you saying that, when the car is moving away, the light reflected from the front of the car travels slower than the light reflected from the rear?

The fact that it was drawn by a cartoonist makes more sense to me.
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No. The light travels at the same speed no matter what. The light left the front of the car longer ago than the light left the back of the car. It's exactly the same thing that stretches the photons and thus shifts them towards the red.
 
bilby said:
Wiploc said:
Loren Pechtel said:
While there obviously would be a Lorentz contraction involved in the car that's not what the cartoon shows. That is purely the doppler effect at work--the light turns blue because it's compressed, the light turns red because it's stretched out. The image carried by the light is compressed/stretched the same as the photons themselves.
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That's not physics. It's a cartoonist's misunderstanding of physics.
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You guys are aware that an approaching blue car doesn't actually appear red after it passes you, in real life.

Aren't you?
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Because in real life the car isn't moving at a relativistic velocity.
 
Loren Pechtel said:
bilby said:
You guys are aware that an approaching blue car doesn't actually appear red after it passes you, in real life.

Aren't you?
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Because in real life the car isn't moving at a relativistic velocity.
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It's not in the cartoon, either. If it was, it would burn up due to the massive heat generated by the compression of the atmosphere it would cause. The surroundings, including the observer and the road itself would be destroyed in a massive fireball.
 
Loren Pechtel said:
The light travels at the same speed no matter what.
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Stipulated.



The light left the front of the car longer ago than the light left the back of the car.
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It's true, regardless of whether the car is approaching or departing, that the far end of the car is farther away than the near end of the car. I don't see how you can parlay that into a claim that the car looks shorter while approaching.



It's exactly the same thing that stretches the photons and thus shifts them towards the red.
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Waves can seem longer when you're leaving the light source (or when the light source is leaving you). We can say that the waves are stretched, if you want, though that is a matter of viewpoint rather than of truth. But the notion of stretched photons is new to me. I don't think it's a thing.

In any case, I don't see an argument that it makes the car look longer.
 
Wiploc said:
Stipulated.





It's true, regardless of whether the car is approaching or departing, that the far end of the car is farther away than the near end of the car. I don't see how you can parlay that into a claim that the car looks shorter while approaching.



It's exactly the same thing that stretches the photons and thus shifts them towards the red.
Click to expand...

Waves can seem longer when you're leaving the light source (or when the light source is leaving you). We can say that the waves are stretched, if you want, though that is a matter of viewpoint rather than of truth. But the notion of stretched photons is new to me. I don't think it's a thing.

In any case, I don't see an argument that it makes the car look longer.
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[YOUTUBE]Oeg29j2EZi8[/YOUTUBE]
 
George S said:
Wiploc said:
Stipulated.





It's true, regardless of whether the car is approaching or departing, that the far end of the car is farther away than the near end of the car. I don't see how you can parlay that into a claim that the car looks shorter while approaching.



It's exactly the same thing that stretches the photons and thus shifts them towards the red.
Click to expand...

Waves can seem longer when you're leaving the light source (or when the light source is leaving you). We can say that the waves are stretched, if you want, though that is a matter of viewpoint rather than of truth. But the notion of stretched photons is new to me. I don't think it's a thing.

In any case, I don't see an argument that it makes the car look longer.
Click to expand...

[YOUTUBE]Oeg29j2EZi8[/YOUTUBE]
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What is the relevance? I had never concerned myself with how to find those angles but it's obvious they must exist and that they're not 90. I don't see how it has anything to do with how long the car looks, though.
 
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