Do Lights Move at the Same Speed?

[Kaleb OLeary]

First I want to say that I plan to study mathematics and physics in college, so I do not know how a lot of things work exactly since I have not really had a formal physics class.
I was wondering if all light moves the same speed, or can some light move faster than other lights for certain reasons. Like, for example, if you are standing and shoot a gun and then get on a jet that is going 100’s of mph and shoot a gun in the direction you move, the bullet that you shot on the jet will obviously technically be moving faster, though relative to your position it seems like it is moving the same speed in both instances. My question is if light follows the same properties.

 

[Drakkith]

It turns out that light does not follow the same property as a bullet. Its speed is the same for all observers moving inertially. That is, for all observers who aren't accelerating. So if you are standing on a moving train and shine a flashlight out the back, the speed of that light is the same for you as it is for your friend on the platform you are passing. Instead of slowing down, the light, as seen by your friend on the platform, redshifts, going to a lower frequency than you yourself see it. If you were to shine it out the front instead, then the light would blueshift to a higher frequency according to your friend.

 

[Mark44]

First I want to say that I plan to study mathematics and physics in college, so I do not know how a lot of things work exactly since I have not really had a formal physics class.
I was wondering if all light moves the same speed, or can some light move faster than other lights for certain reasons.

Light and other forms of radiation move at the same speed through a vacuum. Other media, such as air, glass, etc. lower the speed.

Like, for example, if you are standing and shoot a gun and then get on a jet that is going 100’s of mph and shoot a gun in the direction you move, the bullet that you shot on the jet will obviously technically be moving faster, though relative to your position it seems like it is moving the same speed in both instances. My question is if light follows the same properties.

No. If you have a bullet with a light on it, and fire a bullet at 3000 ft/sec, the light that is emitted still moves at the speed of light. When you study physics more you'll see the reason for this.

 

[sophiecentaur]

the jet will obviously technically be moving faster, though relative to your position

This statement totally ignores Special relativity. You just can't do that, as has been proved for a hundred years or more of theory and experiment,

 

[Cutter Ketch]

I think others may have misunderstood, but your bullet example is correct. The observer on the ground sees the bullet moving faster than the observer on the jet. The speed for the observer on the ground is the speed seen by the observer on the jet plus the speed of the jet. That is called classical or Newtonian relativity and it is what our experience tells us we should expect to be true for baseballs, bullets, or light.

So imagine the confusion and debate at the turn of the last century when it was found that no matter what the circumstance all measurements of the speed of light came out the same. Although they didn’t exactly do your jet experiment, the essence of what they had discovered is that with light instead of bullets the observer on the ground and the observer on the jet would measure the same speed. This blew everybody’s mind and they could not believe it could be true. They certainly couldn’t explain it.

Then Einstein published his Theory of Relativity. He explained it with thought experiments including yours (although rockets rather than jets). Say light is fired from the tail of a rocket toward the nose of the rocket. An observer on the rocket sees the light travel the length of the rocket. He measures the time between firing the light and the light hitting the target, and calculating distance over time he finds that the light traveled at the speed of light. Another observer in a passing rocket sees the light travel a greater distance due to the relative motion. He measures the time between firing the light and the light hitting the target. He calculates distance over time and also finds that the light traveled at the speed of light. They measure different distances, but they both observe the same speed? Einstein reasoned the only way this can be true is if their clocks are moving at different speeds. Relative motion causes a difference in how time is experienced.

This blew everybody’s mind and they could not believe it was true. It has so many bizarre and easily measurable consequences, so science put it to the test. Turns out it’s true, and all of those bizarre consequences really do happen.

 

[lightarrow]

Just to add that light has nothing particular in this behaviour, the same would be true for every other (massless) object moving at the maximum possible speed (that is, light speed in vacuum) and it's approximately true for non-massless objects moving very near to light speed, as fast particles in an accelerator.

--
lightarrow

 

[phinds]

@Kaleb OLeary one of the things that your going to have to do if you want to study science is learn early on how to do research when you don't understand something. Asking a question on an internet forum certainly IS a kind of research but it's often not the most productive kind. You should develop your ability to Google things to figure stuff out on your own. Care is required of course because so much of what's on the internet is just plain wrong, but for very well understood subjects like the speed of light, Wikipedia can often be trusted.

And by the way, welcome to the forum.