# Is light infinitely fast?

okay im going to explain this question through a scenario.

Person A and person B are standing side by side on a linear racetrack, somwhere in space. Both are unaffected by gravity and both are at a complete rest, in space. Person A starts to accelerate, at the speed of light in 0 seconds, following a foward, linear path. At the exact same point of time, Person B shines a linear beam of light in the same direction. So Person A and the Light Beam is travelling side by side at the speed of light. Person A would expect to see the tip of the light beam traveling beside him at the same speed, but instead, he sees the light beam traveling a head him (1x the speed of light). How is this possible? It is because by traveling at the speed of light, Person A is actually traveling faster through time and thus he would see the lightbeam accelerated in time. And it is impossible for him to catch up with the beam, even if he increases his speed to 10x the speed of light, the light beam still seems to be travelling at the constant speed of light. This is what scientist say. And it is proven. we humans on earth are actually moving in space at fast speeds, by the movement of the earth, the solar system and the galaxy. SImilarly, other stars and galaxies are also moving at different speeds from each other. So we humans on earth would expect to see that light coming from this stars and galaxies to vary slightly in speed, however, the fact is that all the light coming from any direction, travels at the exact speed of light.

Now lets look again at the previous scenario. Person A and B standing side by side again. But this time, Both person A and B starts accelerating at the speed of light in 0 seconds(instantaneously). Person A would expect to see person B running at the same speed right beside him, and person B, vice versa. But according to the scientist, by travelling at the speed of light, person A travels faster through time, and thus should see that person B accelerated in time, ant thus moving faster and ahead of him. But how is this possible? Both of them are travelling at the same speed, and thus should be experiencing the same perspective of time.

So scenario 1 cant possibly be true, unless ofcorse, light is infinitely fast, and the only reason we see it traveling at the speed of light, is because that is the limits of time itself, Time just wont allow us to view the light traveling infinitely fast.

Im really confused here, HELP!

Thank you arainia, things are starting to make sense. It also means that my previous sources were bullshit.

Okay lets set up another scenario.

I am on planet earth. I want to visit my alien friends on a distant planet of a distant star, which is 10 lightyears away.

So i get on a spaceship that can accelerate to 99.999% of the speed of light in 0 seconds. I told my friends on earth that i would give them a call when i reach the alien planet. So the spaceship was launched on january 2010. My friends on earth saw the ship launch off at the speed of light towards the star. “For 10 years, they could look up with a telescope and see me flying through space. When they look closely, through a window in the cockpit, they observed that my movements were very very slow, almost frozen. 20 years has passed on earth, when my friends finally recieved a radio call from me.(it takes another 10 years for the radio message to reach from that planet to earth).” This were my friends observations.

But i observed things differently. As i lanched, It appeared to me that i was traveling FASTER THAN THE SPEED OF LIGHT. And it only took me 1 minute to reach the planet. This is because i was traveling very close to the speed of light and thus was moving way faster through time, compared to my friends on earth.

TRUE or FALSE?

Your explanation says that this is true. But if this is true, Imagine if instead of travelling at the 99.9999% of the speed of light, i traveled exactly at the speed of light, and The trip appeared to be instantaneous to me, Which means that i must have traveled INFINITELY FAST in my perspective.

True?

To zixin:

I do understand time dialation. For example, when a person travels at 99.999% of the speed of light, his clock ticks way slower when an observer who is stationary compares it with his own clock. However, the person traveling at the 99.999%the speed of light doesnt experience a slowmo effect, he experiences time normally.

If you actually read my second scenario carefully, you would see that i actually included the time dilation effect.

Lets go back to the scenario. Lets say that my ship travels exactly at the speed of light. My friends on earth would ofcorse see that my space ship is traveling at 3×10power8 meters per second. and that it takes the light 10 years to reach the planet. HOWEVER, because of time dilation, when I travel at the speed of light, my clock would appear to be frozen to an observer on earth. So for me, at that frozen time, which is an infinitely small amount of time, i would have traveled from earth to that planet, in other words, teleportation

You say that this is not true. You say that i would experience 10 years to reach that planet. If this is true, then theres no time dilation at all, since the people on earth sees that my spaceship takes exactly 10 years to reach the planet too.

So in conclusion, light travels infinitely fast, acording to its own perspective. THe only reason we see it traveling at 300 million meters per second is because of time dilation.

Somone prove me wrong

>Is light infinitely fast?

No. The speed of light is about 3*10^8 meters per second (a little less, actually). Furthermore, it appears to move at this speed for all observers, regardless of their own motion.

>both are at a complete rest, in space.

There isn’t really any such thing as ‘at rest’ in relativistic terms, since the motion of an object is relative to the positions of other objects. However, we can imagine that two people start more or less at rest relative to the rest of the Universe and each other.

>How is this possible? It is because by traveling at the speed of light, Person A is actually traveling faster through time and thus he would see the lightbeam accelerated in time.

No, you’ve got it backwards. They’re going SLOWER in time (infinitely slower in fact), which is why the light appears to move faster relative to them from their point of view than from Person B’s point of view. If time were running at a higher, but finite, speed for them, they would observe the light beam moving with them at the same speed precisely as we would expect, but this is not what happens.

>even if he increases his speed to 10x the speed of light

That too is impossible. He can never see anything else as moving faster than the speed of light, nor can anyone else see him omoving faster than the speed of light. As he puts more energy into his motion, he merely approaches the speed of light. If he is already moving at the speed of light (which is impossible) then his speed would not change because the energy would effectively be put towards accelerating an infinitely large mass. This is why you need an infinite amount of energy to actually reach the speed of light in the first place.

>Person A and B standing side by side again. But this time, Both person A and B starts accelerating at the speed of light in 0 seconds(instantaneously). Person A would expect to see person B running at the same speed right beside him, and person B, vice versa.

That is what they actually would see. Since their relative motion would be zero, each would also see the other’s relative motion as zero. Notice how we have a bit of a paradox here in that if you’re moving at the speed of light, light will appear to by you at the speed of light, but another object moving with you at the same speed has to have zero apparent speed. However, one would think that since Person B and light both move at the speed of light, the same behavior should be seen for both of them. This paradox serves to highlight the impossibility of actually reaching the speed of light in the first place.

>My friends on earth saw the ship launch off at the speed of light towards the star.

Or rather, at 99.999% of the speed of light, according to what you said before. There’s actually a very big difference; effectively, the difference between a finite quantity and an infinite quantity.

>As i lanched, It appeared to me that i was traveling FASTER THAN THE SPEED OF LIGHT. And it only took me 1 minute to reach the planet.

This isn’t entirely correct. Although you may well observe yourself reaching the planet in only one minute, you would never see anything going past you faster than the speed of light. This is because space also shrinks in your direction of motion. So for example, the people on Earth would see your spaceship much shorter from front to back than it is when it is stopped, and you would see the entire rest of the Universe squeezed down like a pancake in the direction of your motion. Your destination planet would not appear to approach you faster than the speed of light because you would appear to be only traversing a relatively small amount of space (no pun intended) during that one minute. Once you slowed down to a stop, space would appear to go back to normal and you could look back and see the distance of ten light years between you and your starting point.

>You say that i would experience 10 years to reach that planet. If this is true, then theres no time dilation at all, since the people on earth sees that my spaceship takes exactly 10 years to reach the planet too.

That’s correct.

>So in conclusion, light travels infinitely fast, acording to its own perspective.

That’s also correct, in a way. Although personally, I think it is more accurate simply to say that photons do not experience subjective time. In other words, from a photon’s point of view, its starting point and its ending point are the same point in space, and its starting time and ending time are the same instant. This is consistent with both the time and space dilation effects mentioned above.