# If I were in a space ship traveling at the speed of light and turned on my headlights what would happen?

I mean like would I see the light in front of the ship? Would they really project or would this be an example of a Fitzgerald contraction?

Observing members: 0 Composing members: 0

Too bad I fit the stereotype of “girls suck at physics”....but I love the question!

squirbel (4292)

As you approach the speed of light, space seems to contract in the direction you’re going. From your frame of reference, the light would seem to be moving at the speed of light.

cwilbur (14194)

I believe the general theory states the closer you get to the speed of light, the slower time travels, therefore you can never actually get to the speed of light…. therefore there should always be some sort of projection….

paulipaul (27)

@cwilbur, true

@paulipaul, it is ‘physically’ impossible for anything besides light to travel at light speed. In order for anything with non-zero mass to travel at light speed you would need an infinite amount of energy, which is not possible.

brownlemur (4081)

cwilbur is correct. You’d see the headlights project in front of you relative to your position.

A partical moving at the speed of light would have infinite mass, which is obviously impossible. However, if you were theoretically traveling at the speed of light you would probably not see any light ahead of your ship. Sorry cwilbur, but you’re wrong because light’s speed is constant, meaning that no other factors can affect it.

Rogy (1)

cwilbur is actually right. sorry, I don’t have the time to explain exactly why cwilbur is right, but if you want an understandable explanation, I suggest reading Brian Greene’s The Elegant Universe and The Fabric of the Cosmos.

brownlemur (4081)

Well I took a class on this. Sorry Rogy, the speed of light is NOT constant, it is effected by the medium by which is travels. Of course, if there is no medium, (like in space) then its constant, and faster than being in a medium (air, water etc).
Anyway, since your space ship can’t theoretically go the speed of light as has been explained, lets assume you go .999 times the speed of light, so your really close. In that case, from your reference, you see the headlights’ light project out away from you at the speed of light normally. From a bystander who is not moving relative to you, then in his reference, the headlights light travels at the speed of light relative to HIM not you, and you travel at .999 times the speed of light. So to him, the light is just barely going faster than you. This two statements seem contradictory, but it all depends on what frame your looking at the situation from. All this stuff leads to time dilation and length contraction which makes things quite interesting…
Ok, time for class, bye bye

cwilbur is right, speed depends on a frame of reference, from your reference point in the spaceship, the light would appear to be moving at the speed of light

@rogy, the speed of light is a constant (given that the constant is different based on what the light is moving through, like 8lightminutesaway points out)...but its way more complicated than that

this is one of Einsteins fundamental postulates of special relativity, that light propogates at the same constant speed regardless of any motion of its source or motion of the observer. Light travels at c relative to the observer. Always.

It has to do with the relative stretching or contracting of the time and space dimensions that occur when you move. You will observe space and time differently than an observer moving relative to your frame of reference.

An example of this, if you hold two clocks in your hands and they show the exact same time, then your friend takes one clock up in a plane and flies around the world while you hold the other clock in your hand, when your friend lands back in the same spot, comes out of the plane and puts the clock back in your hand, they will read different times.
Decent explanation

@brownlemur, Brian Greene is a good explanation

also, if you like math, look up Lorentz transforms

jdvanderk (155)

Yeah, I think they actually did the airplane clock test that jdvanderk mentioned back in the 50s or something with some uber accurate clocks and the one that came back from the flight was ever so slightly behind. That proves time dilation for me :)

or