If your car could travel at the speed of light would your headlights work

This is a statement asked by the comedian Steven Wright that this author will attempt to answer.

First, what is the speed of light. It is a constant at which a photon travels from one point to another. This rate of travel is universally known as 299,792,458 meters per second. A photon travels at this rate through the vacuum of space without any impedance. Since a photon has no weight it can also be thought to maintain this speed even within dense atmospheres.

Now the summarization of special relativity and how it answers the above question. Remember first that movement is relative. If we are in a moving vehicle and jump we do not, all of a sudden, fly backwards. We are moving relative to the speed of the vehicle we are in. Therefore, comes the first possible way to explain the question. Since the car is moving at the speed of light the photons projected from the head lights would be moving at this same relative speed before being projected out into space. Therefore, of course the lights would work, because there actual speed would be the speed of light plus the speed of light that they throw off. Another explanation could be no they do not work. The speed of light is a constant. If something reaches this speed a photon could not individually exceed that speed and so would not exit the lamp. Relativity basically means that we see things relative to our position. Movement in these terms is a concept based on position. We could say that we do not move, but the universe moves around us and be totally justified, despite the scientific evidence. Relativity would then have us believe that the car could move at the speed of light and have its head lights shine, or not. It depends on your perspective. If you are in the car moving quickly along, you possibly perceive no movement. Therefore, because there is no relative movement the photons would exit the head lights.

It can be stated in several different ways, and intelligently argued, but the fact is that no one knows because we haven’t gone that fast yet.

A few inane facts.

  • A car can reach a rate exceeding the speed of sound (343 meter per second) but is still 874,030 times slower than a photon.

  • A photon is a particle with no apparent mass. It has the characteristics of both a particle and a wave.

  • There are two theories of relativity. Special relativity has to do with movement and general relativity speculates on gravity.

20 thoughts on “If your car could travel at the speed of light would your headlights work”

  1. hey stumblerz where you come up with such crazy title? I mean really what the h**K is this, i never thought about it.

  2. Vague topic to talk about, but i am not an expert in the field and so I cannot talk about it, but this is puzzling for sure

  3. I see these rules do not apply to Anime shows, but day will come when we will be riding at speed of light.

  4. First of all, you need to realize that when you say you are traveling at the speed of light, that has to be with respect to, or relative to, something else. It is an underlying fundamental assumption of Einstein’s special theory of relativity that uniform, non-accelerated motion has no meaning of and by itself. That is, there is, by assumption, no meaning to the idea of moving uniformly at the speed of light in an empty universe. That state is completely equivalent to being at rest in an empty universe..

    I preface my answer with this comment because it leads immediately to the answer to the question. Imagine that you are in your car ‘traveling at the speed of light’ and that you turn on your headlights. That state of motion is utterly equivalent to being at rest in an empty universe. Since, when at rest, the light from your headlights would be launched forward from your car at the speed of light, relative to you, with a certain color spectrum, that is exactly what would happen if somehow you could be moving instead at the speed of light.

    In other words, the presence or absence of other objects or matter in the universe relative to which, if present, you could make a determination that you were moving at the speed of light makes absolutely no difference to your own experiences and experiments. The light that you launch behaves in exactly the same way whether the other referential matter exists or not.

    This leads into another interesting question, however. And that is whether the rest of the matter (mass) in the universe in some way affects your own local observations. So far this question has come up in relation to theories of gravity. If effect, the question is how does the universal gravitational constant, G, which determines how strongly gravitating masses attract each other, know what value to assume if there is no other mass in the universe. Mach proposed, essentially on philosophical grounds, that G must be determined by the sum total of all of the mass in the universe. Einstein assumed in his General Theory of Relativity that G is simply a universal constant, independent of the specific mass distribution of the universe. On the other hand, Brans and Dicke later proposed a so-called scalar-tensor theory of gravity in which the local value of G depends upon the rest of the mass in the universe through an additional scalar field that does not appear in Einstein’s theory.

    Answered by: Warren Davis, Ph.D., President, Davis Associates, Inc., Newton, MA USA

  5. Question

    If you’re in a car traveling at the speed of light and you turn your headlights on, does anything happen?

    Asked by: Nicole


    Your question contradicts Einstein’s Special Theory of Relativity which states that no object with mass CAN travel at, or above, the speed of light (c). As your car approaches c, its resistance to acceleration (mass) increases so that it would take an impossibly infinite force to actually reach c. Your question, then, is based on an impossible premise. It’s like asking ‘What would happen if I reached the North Pole and kept going north?’

    As you approach the speed of light with your headlights on, however, you would still measure the light beam racing away from your car at 186,000 miles per second (c). A ‘stationary’ observer watching this happen, though, would not then measure the beam’s speed at almost twice c. Relativity says that all observers always get the same measurement for c.

    While that may not sound logical or plausible, it happens because what we normally think of as fixed concepts–length and time–are both variable at high speeds. If you observed a car travelling past you at close to c, its length in the direction of travel would appear shortened and the passage of time on board would appear slowed down.

    Although these ideas sound strange to all of us not used to moving at relativistic speeds, they have all been confirmed experimentally.

    Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor

  6. It is hard understand this . But if you go this fast you won’t hear anything right because the speed of sound won’t be able to catch up with you .

  7. Josh, I feel Efrain is right if we consider the cars of today. What he seems to have forgotten is that we do not have cars today which race at the speed of light. So he does not imagine that if someday we do have cars that do run at this speed they will be having parts which can withstand that speed and pressure.

  8. I have just been wondering about the roads we will need to build for these type of vehicles to run on and the tyres we will need to manufacture to resist the heat that this will build… WOW!!!!

  9. If car is travelling through the space, your velocity can not be measured because velocity is relative. So light rays must leave the car, with the speed of light, relative to it.

  10. what will happen if sun disappear all of sudden ? What about speed of gravity pull equal to or more than speed of light ?

  11. it can be possible to touch speed of light if all the parameters in any vechicle is maintained(pressure,temp…….)and most imp if anythng travels wth tat speed the mass is infinite and th accelerate tat mass we need infinite source of energy the energy is problem if somebody discovers the infinite source of energy to accelerate that mass , scientists are working on that then it vl be possible but most difficult as the vechile is a mass(matter) composed of energetic particles if that travel wth tat speed (light) then it will be converted into energy (eltromagnetic waves)indeed

  12. “…but the fact is that no one knows because we haven’t gone that fast yet.”

    You are a moron. E=mc2 states the impossibility of such a question.

  13. this information is for all…
    did u undrestand the meaning of word “theory”…theory’s are just imagination and assumption ….infact you and me both can write any theory…

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