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# Scary relativity

209 replies to this topic

### #201 EJN

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Posted 12 December 2013 - 09:55 PM

They're halogen with Sylvania 9003 bulbs.

### #202 Charlie B

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Posted 13 December 2013 - 07:24 AM

Quote:

They're halogen with Sylvania 9003 bulbs.

The light from the headlights are moving at c, but the white Sylvania 9003 bulbs are blue shifted if coming at you and red shifted if moving away. There is no case where the light moves faster than c in any reference frame.

Charlie B

### #203 brentwood

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Posted 13 December 2013 - 08:57 AM

Quote:

They're halogen with Sylvania 9003 bulbs.

The light from the headlights are moving at c, but the white Sylvania 9003 bulbs are blue shifted if coming at you and red shifted if moving away. There is no case where the light moves faster than c in any reference frame.

Charlie B

See what I mean? As soon as someone asks a question about Relativity, it is immediately thought that the basic premise of Relativity, c is a constant, is being challenged. So by a car doing .9c and putting on its headlights, the light is going to shoot away from the car at 1.9c. I think that we all agree that this does NOT happen. Light leaves the car at c.
What I am asking is that if an observer were standing off to the side and the car went past you some distance away, and you could somehow see the light and measure its speed at c, and the car's speed at .9c, it would LOOK as though the light was leaving the car at .10c! Because of the time dilation, the car driver would see nothing different, to him the light would still be streaking away from him at c.
Apparently this is wrong, the geometry is wrong, or the way the observer 'sees' is wrong, but no one will explain it!
I did read somewhere that a physicist wrote "I am no longer going to try and teach Relativity to those who cannot be bothered to learn it" or something like that!

### #204 PeterR280

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Posted 13 December 2013 - 10:06 AM

You are right Brentwood you would see a relative velocity of .1c between the car and light beam. The car would however see the light as leaving at c.

### #205 The Mighty Mo

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Posted 13 December 2013 - 10:09 AM

Post deleted by The Mighty Mo

### #206 PeterR280

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Posted 13 December 2013 - 10:13 AM

Mighty Mo. If the car were stationary and you accelerated would things look any different? Who would age slower?

### #207 The Mighty Mo

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Posted 13 December 2013 - 10:18 AM

Sorry Peter, I deleted my post above, as I realized it was saying the same thing as you and Brent. If you were the one that was accelerated, and not the car, WRT the rest of the universe, then it would be you, the observer, that would age more slowly as time will slow down for you. But you won't realize it until you stop, everything would appear normal for you while you're "moving".

### #208 brentwood

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Posted 13 December 2013 - 10:37 AM

Thank you Peter and Mo for taking the time to read what I was saying. I think I'll treat myself to a chocolate biscuit & an Irish Coffee!

### #209 Charlie B

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Posted 13 December 2013 - 03:17 PM

What I am asking is that if an observer were standing off to the side and the car went past you some distance away, and you could somehow see the light and measure its speed at c, and the car's speed at .9c, it would LOOK as though the light was leaving the car at .10c!

I think that I'm not clear. The car would appear to be moving at 0.9 c, if not moving toward or away from you. The light would be emitted from the car and would be and appear to be to be moving at c. Light is not a particle that, like a bullet, can be shot from the car with a difference in velocity. It always moves at c and always appears to move at c. You cannot see the car and light as separate entities. Remember you see the car by light as well, which implies that your seeing the car and the light from the headlight would be by light leaving the car at the same time.

Regards,

Charlie B

### #210 brentwood

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Posted 13 December 2013 - 04:09 PM

Well you could say that the car flashed its lights once and it would still work, the car has a light on it so you can see it. The 'lump' of light from the headlights is moving through space at c, while the car is seen to be at .9c. The RELATIVE speed of the light and the car is .10c, so you could say that it LOOKS as though the light is leaving the car at .10c. To the driver of the car though it looks normal, the headlights are lighting up the way ahead.

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