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# Faster than the speed of light?

#### Switch

##### New member
Here's something that just came to me out of nowhere.

If you're on a fast moving vehicle and you shine your laser in front of it, would the photons shooting from your laser travel a little bit faster than the normal speed of light? :-/

#### roSSco

##### New member
Einstein said no. ;D

#### Switch

##### New member
Then, if you were to travel at the speed of light and turn on your headlights you wouldn't be able to see at night?

##### New member
If you make yourself and your lights massless and travel at the speed of light, then the light wouldn't outrun you, you would run the same speed. But that "massless" requirement is, as one of my professors would say, "non-trivial".

#### Cyparagon

##### Well-known member
Yep, that'd be the diet from hell.

#### steve001

##### Well-known member
The speed of light in a vacuum is invariant no matter what your speed.
If you were to travel on a beam of light in a vacuum with a flashlight -or laser- in this case and shine it in the same direction you were traveling you'd see the beam from the flashlight or laser travel at the speed of light. Read Einsteins Theory of Relativity

#### Switch

##### New member
Yea that's what I've said.Besides, light does have mass right? :-/

#### philguy

##### New member
I'd say light has mass.

The problem here is the so-called Lorentz-Transformation which means a contraction of space as speed increases. So your headlights' photons move at c, compared to you, and with c, compared to a bystander "at rest" (ha, define that!) - no matter what your speed is.
Sick and twisted it is, and like a hard blow to the stomach.

So, photons always move with the speed of light (i.e. c, i.e. 2.99e8m/s) and pretty much don't give anything about what surround them or how fast any observer flies with them. Tey will just always tell you their speed is c.

L

#### likewhat

##### Guest
The light would be blue shifted to an outside observer I think.

#### Switch

##### New member
philguy said:
I'd say light has mass.

The problem here is the so-called Lorentz-Transformation which means a contraction of space as speed increases. So your headlights' photons move at c, compared to you, and with c, compared to a bystander "at rest" (ha, define that!) - no matter what your speed is.
Sick and twisted it is, and like a hard blow to the stomach.

So, photons always move with the speed of light (i.e. c, i.e. 2.99e8m/s) and pretty much don't give anything about what surround them or how fast any observer flies with them. Tey will just always tell you their speed is c.
Wow , that's interesting stuff.I'm probably way behind in physics to be asking questions like this anyway.But still, would that mean that the speed of light is the maximum or something?Like if you go faster than that the space warps so that you keep your speed? :-/

Anyway this is getting way offtopic, I posted it here cause it kinda had something to do with a laser ;D

#### philguy

##### New member
Well, try going as fast as c before you plan on going beyond that. Because even approaching c is a pain in the rear. Deal is, the faster you get, the higher your mass. Or in other words, around c your body weight is no longer 150 pounds, but all of a sudden 100 tons! And try to accelerate 100tons of mass! So if you keep on accelerating, you get asymptotically to c, but at the cost of a huge energy bill.
Thus so far, the laws of physics don't need to worry about you going faster than light...

about likewhat's statement: Just about. If you fly to the right at "somepercentageofc", the image you receive will be "blue-shifted", i.e. it has a bluish hue. This is due to the fact that all photons hitting you appear to have a shorter wavelength. Check optical Doppler effect for that.
Likewise, if you were to look backwards (i.e., to the left, for an observer at rests pov), everything looks a bit reddish.
On a side note, another interesting effect is that your field of view is being expanded, until, at c, the image of everything happening around you is compressed into a tiny dot in front of you.

So you can therefore easily calculate how fast you would need to "run", to turn your 532 greenie into a 473 blue laser.

A friend of mine used to have a time where he said "can you make that lethal?" about just about every topic we dealt with in physics.
So we calculated how fast he needed to move his 125mW greenie so that it could kill a person from the gamma-radiation-shifted photons, dying due to radiation poisoning. I think it was about one millimeter per second short of c...

edit: go to spacetimetravel.com (or tempolimit-lichtgeschwindigkeit.de if you are comfortable with german...) to watch some nice animations showing how it would look like if we were able to interact with the speed of light in our every-day lives.
The german page has a few more examples, if you just click onto the videos.

#### Switch

##### New member
Is the 100 tons figure due to gravity?Or g force? Or some other force i'm unaware of? :-/

Also by asymptotically I understand that you still can't quite touch c no matter how hard you try.What's so special about the speed of light that makes it impossible to touch or pass?Is it the maximum speed allowed in our universe ;D ?I thought that it was just an insanely big speed.....But there I say again...I'm way to behind in physics here... :-/

Anyway it's pretty cool that you can make a 555nm diode out of an IR one

#### RA_pierce

##### Well-known member
100 tons? How does this happen?

If you were to run at the speed of light, think about what would happen if you tripped. Or hit a wall... (of course were not counting the friction of skin vs air, that would just rip you to pieces). Would the momentum be enough to get a human body through a concrete wall?- headfirst, of course ;D

#### Switch

##### New member
Moving a solid object at that speed through air, I don't think friction is the only thing that's gonna cause problems I think other bad stuff would happen to the human body before hitting the concrete wall ;D

#### FireMyLaser

##### Well-known member
What if u travel at the speed of light and turnd on the beam backwards, would it just stop?

#### Switch

##### New member
I don't know but it would make sense to me The reason I thought about this is the fact that supersonic fighters still have machineguns, and the bullets shot from those in mid flight travel faster than they would on the ground due to the momentum they already have.So I thought , if photons have mass, they would be subjected to the same phenomena...

philguy said:
So, photons always move with the speed of light
I just remebered this: What about those guys that slowed light down? Or the ones that stoped a beam of light and released it later? :-/