Faster than light travel? If everything is relative?

Question

An object leaves earth, attains light speed, also being observed from earth. It then switches two lights 'on' one forward the other aft. Light will/should leave from these two points at the speed of light? Now the question.
1) Will light at the forward end leave at the speed of light relative to the craft and from earth appear to exceed the speed of light?
2) Light leaving at the aft end of the craft will leave at the speed of light relative to the craft but since the craft is already traveling at the speed of light in the opposite direction, will light appear on earth as stopped?
If we have to accept that everything is relative. Then light in question 1, will travel faster than the speed of light, relative to earth where the object emitting light left from. Light leaving the craft (aft) can never be seen since it will never reach earth owing to its source receeding at the speed of light.
How do we know the universe is expanding if it does so at light speed, another question?

Answer 1

This question requires to be considered from the view point of an observer on earth.

First, the spaceship will not reach speed of light since an infinite amount of energy is required for this.

Second, light waves from the front will not be observed since it is not travelling towards us. This prevents the observer from coming to the conclusion that the light is travelling any faster.

If ever it was possible to observe the front light, we should also take into account time dilation. Now, on earth, we would observe that everything has slowed to a tiny pace on the spaceship and that the light seems to be stuck on the front of the ship. The observer on the ship will however, live the event into "slow motion" and to him/her the light will not be stuck but it will be moving at the speed of light.


Coming to the light which is emitted from the back, we should understand that the light will never reach us, not because of relative speed but because, at light speed, the time dilates to infinity so that the people on the ship takes an infinite time to switch the lights on and that mean never.

Answer 2

Light in a vacuum only has one speed. It is independent of the space craft that it is mounted on. Light has properties of a particle and a wave. Because of the wave property, the photo will not behave according to simple ballistics of particle motion. The speed of the light will not change, what will change is the wave length of the light. If a single light was mounted on the space craft so that it could be observed from all directions. The wave length of the light would be less from viewing the space ship as it left the earth compared to the light seen from the destination.

The people at the site of origin would see the light change color until it would no longer be in the visible light range, but could still be measure by infrared devices until the wavelengths were even longer. The person at the destination would not see anything until after the spacecraft started to decelerate. The measured energy would travel from the microwave band and higher until it pasted through the ultraviolet and finally achieving the same wave length emitted by the light while stationary.

Answer 3

In 1, light can not travel faster than the speed of light, therefore no, it will not appear to be travelling faster than the speed of light. At any given point in time, the light emitted from either lamp will begin travelling back to earth at the speed of light. This is true regardless of the speed either of the craft or of the earth.

In 2, the same applies as above - the light is not trapped within the relativity bubble in the same way that, for example, a cigarette butt thrown from a moving train assumes the speed of the train until it hits the slipstream. As light by definition cannot travel faster than light, it requires a logical absurdity to believe otherwise.

In other words, it is no different to the headlights on your car, except that the speeds involved are higher. If you're driving down the motorway with your lights on, the light does not leave the headlights at 186,000 miles per second + 70 mph.

Answer 4

What we know as speed relates to distance travelled in a given time. This works where speeds are comparatively low. Once you start getting towards the order of the speed of light, the universe behaves very differently. Space and time are distorted. Matter reduces in the dimension of the the direction of travel and time runs more slowly than for a stationary object. These phenomena place a theoretical limit on the speed at which anything may travel. There can be no speed above the limit, just as there can be none below zero. Light travels at infinitessimally less than the maximum.

Now I've said it can't happen, if something travelling at the speed of light swithed on lights facing forwards and backwards, no light would come out of the forward facing one. Whether you use the photon or waveform model, light could not leave the light source faster than the speed of light. There would soon be a build-up of energy on the light source and this would destroy it. The light from the rear light would travel at the speed of light. The object would be travelling at the speed of light. Now the bit where quantum mechanics causes your brain to fall out. The relative speed of the object to the light being emitted would be only 1 x the speed of light.

Answer 5

We can not travel faster than the speed of light. Period. Unlike what a lot of other people are trying to tell you here, it is not just that we don't have the right technology or enough energy. Nothing with mass can EVER travel at the speed of light. This is a physics fact and Einsteins theory of special relativity is based on it. There are hundreds or even thousands of scientific theories and technological devices that rely on the laws from which this idea (that the speed of light cannot be surpassed). It is a tried and true fact.

Answer 6

1: Light travels at the speed of light whatever the speed of its source. The radiation emitted by the spacecraft will have crazy high frequency measured from earth because of time compression (it'll go the wrong way to ever reach it though).

2: no just lower frequency.

(light is radiation between two frequencies, outside of these the photons can be radio waves, gamma and other waves. all manifestations of the same photon at different frequencies) Technically, from Earth the radiation emitted will not be considered light.

We do not know how fast "the universe is expanding", and the initial speed is subject to theories only. We can see that "the universe is expanding" by measuring the distance of other galaxies around us, since they are moving away, it follows that a ball shaped group of galaxies is getting larger. The real question is, however, how big is the place they expand in.....

Answer 7

An observer on earth would see the forward-facing light and the ship move at the same speed. The rear-facing light would also appear to travel at light speed (as all light does to any observer) creating the illusion that the light is travelling twice the speed of light from the spaceship.

The observer on the ship would see nothing unusual i.e. both lights leaving the ship at light speed - worth noting also that observers on the ship would never see the light hit the Earth as both the Earth and rear light are moving away from the ship at the same speed... So it's paradoxical.

Answer 8

It's impossible to answer your question as it stands simply because of the impossibility of reaching light speed. We can't even discuss this theoretically because we'd have to envisage a situation where all the laws of physics broke down and what would be the point of that.

BUT, if we rephrase it a bit - what if you were travelling at 99.99% the speed of light? The very, very strange thing about light is that it always travels at exactly the same speed regardless of your motion - relative to an observer. So doesn't matter if you're in a car at 30mph or a rocket at 100,000 mph - light will always race away from you at the same speed.

I have given a few (I think) easy to understand explanations of relativity recently. If you're interested track back through my answers.

Answer 9

Your question gets to the very heart of special relativity. First of all, the craft cannot travel at the speed of light, but let's say it is traveling at 99% of the speed of light. The observer in the craft will see both light beams traveling away at the speed of light from that point of view, and an Earth bound observer will also see the beams travel at the speed of light from the earth's point of view. I know that this leads to apparent contradictions such as the light having to be in two different places at the same time. What Einstein (and Lorentz) realized is that the way to fix the contradiction is by looking at the concept of "the same time" He realized that what must be true is that the time would NOT be the same! That is the passage of time is different for the two reference frames. That is called "time dilation" and it is one of the consequences of the special theory of relativity, that light travels at the same speed relative to all reference frames.

Answer 10

When you turn on the headlight the photons emitted don"t know they are traveling at light speed. The quantum effect allows the photons to accelerate to the speed of light.This takes place in one-thirty billionths of a second and a distance of one centimeter the light beam will lead at this distance.
When you turn the rear light on the light beam will again accelerate to the speed of light they do not have to worry about the forward speed it does not affect them,the speed of the emitter is irrelevant the photons accelerate away to the speed of light, they will reach earth like any other light.
The universe initially expanded at the speed of light and will do so for a finite length of time.