If I was going the speed of light?

Hi, I’m a 12th grader taking first year Physics. I have a theoretical question about the speed of light. If there was a sealed room that contained me and a lamp, the room as a whole was traveling at the speed of light and I turned the lamp on, would I see the light slowly crawl outward from the light the bulb or would I not see light until I reached me and then see the rest of the room light up slowly? Help!!!
Thanks
Brandon

I have to say neither. You would see the same thing you see now when you turn on a lamp.

The speed of light is the same, no matter how you or the source of light move. That is implicit in Maxwell’s equations, and was one of the basic postulates of Einstein’s theories of relativity.

Therefore, when you and the source are moving together, you cannot measure any difference in the behavior of the light from the lamp. Even if you were in motion relative to the source, the speed of the light would seem the same. You might not agree with all other observers exactly when the lamp came on, however.

I can see I’ve probably raised more questions
than I’ve answered. That will serve to keep this thread going, though.


“If you prick me, do I not…leak?” --Lt. Commander Data

This has been answered before so you may want to check the archives. The fact is velocities are not additive. i.e. if you are travelling 24000 mph and shoot a gun with the bullet at 6000 mph (all theoretical speeds of course) the end velocity of the bullet is not 30000 mph. Unfortunately, I can’t remember the formula but does become more significant at higher speeds.

The speed of light is a constant throughout the universe for all observers, regardless of how fast they are going. Let’s assume that the room you are in is travelling at 95% of the speed of light, since it can’t actually travel at the speed of light. This is an inertial reference frame. By the theory of relativity, all inertial reference frames are equally valid. And the speed of light is constant in each.
The light from the lamp would travel from the lamp to you at the speed of light (2.9979 m/s) according to your measurements. If there was a window and I was outside looking in, I would measure the speed of the light emitted by the lamp as the same as you do. It’s a rather tricky concept, especially when you figure the Lorentz transformations into the equation.


“It is not from the benevolence of the butcher, the brewer, or the baker that we expect our dinner, but from their regard to their own interest.” - Adam Smith

I’ve got your equation right here! Consider two objects. The first object moves with velocity v relative to the second object, while the second object moves with velocity u with respect to an observer.

<img src=“http://pads1.pa.msu.edu/courses/1997spring/PHY232/lectures/relativity/vel_ad2.gif” width=“97” height=“84”>


“We can imagine no reason why, with ordinary care, human toes could not be left out of chewing tobacco, and if toes are found . . . it seems to us that somebody has been very careless.” Pillars v. R. J. Reynolds Tobacco Co., 78 So. 365, 366.

Sorry. Paste the address in my previous message into your browser’s address space, hit enter, and be enlightened.


“We can imagine no reason why, with ordinary care, human toes could not be left out of chewing tobacco, and if toes are found . . . it seems to us that somebody has been very careless.” Pillars v. R. J. Reynolds Tobacco Co., 78 So. 365, 366.

To answer the OP directly:

In the room, you are at rest with regard to the lamp. Therefore you don’t see anything different than if you were in your room at home.

It is incorrect to say “the room is moving”. You must say that the room is moving relative to something else. Einsteinian Relativity specifically precludes absolute motion.

When we’re talking about Einsteinian motion, we’re talking about reference frames. A reference frame is just a set of conditions under which you are measuring velocity. Generally speaking, you pick a reference frame that’s convienient.

For instance, if you’re moving with respect to me, there are two interesting reference frames: the one at rest with respect to you (in which I’m moving), and the one at rest with respect to me (in which you are moving). A reference frame is not a real thing, just a conceptual place to “rest your instruments” so to speak.

If you (i.e. the reference frame at rest with respect to yourself) are moving very close to the speed of light relative to the light source, you still see the light moving at the speed of light in your own reference frame.

The reason is because as you move faster relative to an object, your time relative to an object decreases (i.e. you see him “slow down”) exactly enough to make the speed of light exactly the same.


Dr. Crane! Your glockenspiel has come to life!

But aren’t you moving with respect to the luminifous ether.

::gets smacked upside the head::

sorry, geez, you didn’t have to hit me so hard.

You were right to be smacked. The famed Michelson-Morley Experiment, one of science’s great failures, effectively proved that light moves at the same speed regardless of who’s measuring. And don’t worry about how stupid M&M (couldn’t resist) felt. Every scientist wishes he could have a failure so important.

Say you are going 90% the speed of light in your room and you turned on your lamp. It would appear the same as if the room were at rest. Time would be much slower but you wouldn’t notice it. After you slow down your room from 90% the speed of light you would come to the realization that you traveled into the future.


Two wrongs do not make a right…but three lefts do.

Silo: Remember, you can’t just say “you are going 90% the speed of light,” you have to say you’re moving relative to something at that speed.


Catapultam habeo. Nisi pecuniam omnem mihi dabis, ad caput tuum saxum immane mittam.

the question, I beleive was theoretical. In that case peolple can travel the speed of light. Think of yourself at the side of a highway watching a car pass at 70 mph. To you it’s going fast, but to the passenger it feels like sitting in a recliner. If light emits from the bulb at a consant rate, the light emitted should be the same whether sitting in a living room or aboard a vehicle travelling at SOL. The only hole in this theory I can think of is that light isn’t a tangible object so you may turn on a lamp, but pass the emitted light before it reaches your eyes. Of course, you may see light from a reflective source, but have never seen that argument submitted.

Perhaps the biggest reason why a particle with a nonzero rest mass cannot accelerate to the speed of light is because it takes energy to accelerate something, and energy turns into mass if there’s enough of it. OK, this calls for a little example. Let’s say that you’re sitting in a spacecraft. For all of the energy spent to accelerate you at sublight speeds, a small fraction is turned into mass via M=E/C^2 (that’s Mass equals the amount of Energy divided by the Speed of Light squared (C is the Constant in all reference frames)). At low speeds, this really makes no difference because it takes a buttload of energy to add up to even a small amount of mass. But when you are accelerating near to the speed of light, all that mass adds up like a lunch bill everyone dodges. Result? You get a mass that ramps up towards infinity before you can reach the speed of light in a vacuum. It takes an infinite amount of energy to accelerate an infinite mass (just hang with me here), and you only have a few ounces of antimatter left. Oh well, I hear Jupiter is nice this time of year.


“We can imagine no reason why, with ordinary care, human toes could not be left out of chewing tobacco, and if toes are found . . . it seems to us that somebody has been very careless.” Pillars v. R. J. Reynolds Tobacco Co., 78 So. 365, 366.

There is another piece to why you can’t go the speed of light.

As you approach the speed of light time slows down. At the speed of light time stops.

With infinite mass and zero (or should I say null?) time this has the odd side effect of placing you everywhere in the Universe at once.

Neat trick huh?

a) In the case quoted here, this is simple Newtonian physics, and the velocities are additive! (They’re vectors, remember?) I think you are confused between the bullet’s speed relative to the person firing the gun (in motion) VS. the ground speed of the bullet.

Or, if you were on a train going 100 mph and walking in the direction of the train at 3mph, your speed relative to the ground IS 103mph. But, your speed relative to an observer seated on the train is only 3mph.

b) For the OP’s question, refer to Saltire’s posting above.


“They’re coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time… :)” - Napoleon IV

Nice try, Jinx, but no. If your velocities are only in the 100 mph range, then what you said is a near enough approximation to be considered true. But the OP was asking about velocities (near) the speed of light, and at those speeds, you cannot just add velocities the way you do normally. You must use the relativistic equation that Derleth (attempted to) post-- special relativity conspires to ensure that the sum is always less than the speed of light, unless one of the original velocities is itself the speed of light, in which case the speed is exactly the speed of light. In other words, if the train is going at 100 mph relative to the tracks, and you’re walking at 3 mph relative to the train, yes, you’re going 103 mph (near enough) relative to the tracks, but if the train is toolin’ along at .8 c, and you’re walking at .4 c relative to the train, it gets ugly.


“There are only two things that are infinite: The Universe, and human stupidity-- and I’m not sure about the Universe”
–A. Einstein

Um, under what theory? This kind of question really bugs me. Relativity says that even in theory you cannot ever accelerate to the speed of light. There is no theoretical basis to answer the question in the OP.

And furthermore, it should read:
“If I were going at the speed of light?”

:slight_smile:

But isn’t Relativity itself a theory? What I’m saying is since hitting SOL isn’t possible (yet), how can anyone be sure what exactly happens? Also, if anything travelling at SOL turns to mass, how come the sunlight isn’t kicking everyone’s ass? Seems to me if speed can be compared to light, light should be some physical force in order to travel at all. Did I miss a day in physics when this was taught or have I just gone that long without studying?

Actually, if there was a clone of you with a negative mass right next to you, the gravitational attraction between the two of you would actually pull each of you in the same direction. Err, diagram:
<BLOCKQUOTE><font size=“1” face=“Verdana, Arial”>code:</font><HR><pre>
Normal:
(+)—> <—(+)

Instead:
(+)<— <—(-)



As the two of you are pulled to the left, your mass increases, and the mass of your clone does as well. However your clone's mass increases in the negative direction. Therefore, the mass of the system remains constant at 0. The two of you simply breeze past the speed of light.

Wow, posting theoretical physics while drunk is fun!

To elaborate on waterj2’s post:
F = -GMm/r²
(Newton’s Law of Gravity), so if one mass is negative and one is positive, then the force is positive, i.e., repulsive. Now, taking Newton’s Second Law,
F = ma
so a positive mass will accelerate in the same direction as the force, but a negative mass will accelerate in the opposite direction, hence the weirdness of spontaneous acceleration in the previous example. Of course, this presupposes the existence of matter with negative mass… Every serious method yet proposed for dealing with the speed-of-light limitation has required negative mass in some form or another, and we’re still not sure if that’s possible, much less how to do it. sigh. I guess I’ve my work cut out for me…


“There are only two things that are infinite: The Universe, and human stupidity-- and I’m not sure about the Universe”
–A. Einstein