speed of light

Guest

I just thought about the speed of light for a while and I have this question.

At night, the train is travelling 100 mph(with respect to the ground) going north. The train has two headlights. Does this mean that the light coming out from the trains two headlights is the speed of light plus 100mph? Does this mean that the light from the trains headlight travelled FASTER than light?

Does anyone know the answer? thanks.

Guest

hi confused,

according to einstein, the speed of light is constant in vacuum, whoever measures it. so i guess the answer to your question is no, the light from the train did not travel faster than light...

stephen hawking Wink

Guest

Hi Stephen,

I went over Brief History of time, but somehow it doesn't answer my question.

If light is constant in this case, then the speed of the light from the headlight is constant. But what is the light's speed with respect to the ground given that the train is at 100mph? Is it still constant(you answered yes, right)? if it is, then does that mean that the train's speed is zero with respect to the ground? If so, then it now conflicts with the original case that the train was travelling at 100mph?

Which is which?

Thanks.
Confused

PS. "How much choice did God have in constructing the universe?" - Albert Einstein

Guest

Hi Confused,

I'm not an expert (I'm just a fake Stephen Hawking) but I'd like to explain further because I enjoy discussing these things (it's almost like discussing philosophy).

Newtonian physics breaks down when speeds equal to or near the speed of light are involved. Thus, it is not correct to treat the speed of light as being additive or subtractive from the speed of the train. When things get near the speed of light, strange things happen -time slows down, lengths become shorter, mass increases.

For now, the best proof that the speed of light is constant is Einstein's math and the fact that hundreds of experiments have shown so far that that is really the case. Note that thousands of physicists have tried and are still trying to prove Einstein wrong, if only to earn a place in history. But how many of them have succeeded so far? Nada.

That is not to say, however, that the speed of light is really constant. Someday, when our instruments become more accurate, this view may change (science has that habit of changing every now and then). Until then, I'll have to again say that, yes, the speed of light is constant.

Fake Stephen Hawking

Guest

Quantum Physics says Light is not a matter but an electromagnetic radiation in the form of photons. Thus, it has a constant speed regardless of the speed of the source. This is where Einstein gets his theory of relativity. The main reason why the Pedro turns out to be 10 years younger than his brother Pablo after he travelled in the speed of light for 10+ years. The more confusing question here, is that if the train travels in the speed of light, then will the headlamps no longer have a light beam because the train is travelling at the same speed? Einstein's theory says "Yes". I don't have the resource to prove him wrong, so, I say Yes too.

Guest

The velocity of the light will still be equal to nearly 300 000 km/s=c as observed in both train and ground. That is acccording to the special theory of relativity! How come? accroding to the theory, the speed of light is constant at any "frame of reference". And according to Einstien also, no one can travel beyond that speed. Does it mean that the velocity of the train is zero? No, it will not go that way... why?
If you are in the ground, you will observed the light travels at speed equal to c, not equal to c+100mph. If you are in the train, you will observed the same speed. Weird, isn't. But let us go back to the equation of velocity, v=dv/dt, simply, v=d/t. from that equation, we see the effect of time.... and actually... that's the key to that problem.
let me repeat it again...If you are in the train, you will observed that the light travels at c. If you are in the ground, you will observed the same thing, velocity of light=c. . What is therefore the difference? If you are in the ground, it is right to conclude that the time in the train runs slowly... and if you are in the train, you will conclude that the time in the ground runs faster... So the answer to the "why" is because time varies relatively... and the train travels NOT equal to zero...

Hope nadagdagan ko sakit ng ulo ng nagtatanong.... Wink

Guest

yo lalong pampagulo, makikigulo na rin ako. i agree that v=d/t, where d is the distance. but what do you mean by v = dv/dt?. isn't dv/dt = a (acceleration?). just asking. i hope we're all succeeding in confusing mr. confused.

nakigulo na rin

Guest

I agree with "Lalong Pangpagulo". The speed of light will be constant to any observers. But it was not the result of the Special Theory of Relativity, it is actually its foundation. Einstein needed to make this assumption to make his Relativity Theories work.

There is no addition when it comes to speed of light i.e. there is no 1.5x the speed of light even if the source is travelling at 0.5x of the speed of light. However, I remember there are talks regarding super luminal speed (I'm not sure if I got this right) which pertains to ESP and other unexplainable aspects of physics. It is at this point that physics and religion, particularly, buddhism meet. But this is another story....

Guest

Thanks for the correction. It should be v=dl/dt or simply dv/dt. Thanks again!

Guest

v=dl/dt, or simply v= d/t...medyo nagkakamli po kasi ako palagi sa typing. he he he

Guest

the train is moving, not the light

Guest

so maiiwan ang light ng train? hehehe

Guest

aha alam ko na! dahil constant ang light at hindi nagbabago.

so advise ko sa inyo, kapag sumakay kayo ng train at gusto nyong patigilin, buksan nyo lang ang flashlight. hehehehehehehe.....

Guest

aha, the light can't be stationary, otherwise it won't reach anybody and it will be invisible. so both the train and light must moving, except that the train still follows newtonian physics because it doesn't have the speed to exhibit relativistic manifestations.

voila

Guest

yap, the light is moving... remember the unit meters per second, meaning it is moving for a certain distance per unit of time. If it is not moving, then it will have a speed of zero (0) meters per second... right? You might be thinking that the light is not moving at that speed (300k km/s) when you are observing it at the train... that is true if and only if you are also thinking that time is the same when you are travelling and if you are not... The thing that I am saying is... time is different, hence, you can still conlcude that you can still observe the light as travelling at 300k km/s, as always... whether you are in the train, or at rest...