Question Regarding Faster-than-light (also superluminal or FTL)

reply to post by ChaoticOrder


Thank you Chaotic and everyone else for your time. The more I try to learn about this the more questions arise in my pea brain lol!

However, even with gravity space has no resistance to the object. So saying it gains more mass is like saying it grows. The reason we can't propel things faster on Earth is air resistance. There is nothing in space (unless you consider Dark Matter something, which I think actually would break many Laws of Physics by existing).

reply to post by NightFlight


If the speed of light is always constant I think the observer will not see the light move twice as fast. Will the photons/light emitted by the flashlight build up? Maybe we will get an increasingly bright point of light. Who knows. I confused myself

Originally posted by BLKMJK

... I still do not understand WHY or HOW mass increases as the velocity increases. The more I think about it the more tangled up in my head I get.

I hope this will make sense, but I'm gonna give it a shot...

The most basic side-effect of Special Relativity is actually something that a guy by the name of Lorentz came up with before Einstein ever got in on the action: length contraction. According to both Lorentz and Einstein, as an object speeds up, it shrinks in the direction of motion - that is, effectively, it gets shorter.
Take a train, for instance. As the train speeds up along the track (and assuming the track is in a straight line), it gets shorter. Don't worry about why the train gets shorter... this is merely an artifact of nature keeping the speed of light constant (you'll see why/how in a minute). At regular train speeds, the shortening isn't measurable. But, if the train were to speed up to near the speed of light, its length would shrink dramatically, until finally, at the speed of light, the train becomes 2-dimensional (it still has width and height, but its length has contracted to 0).

Now, all of this is according to an external observer. But, what about a passenger on the train? Well, according to them, it's not the train that's moving at the speed of light - it's the stuff outside that's moving by them at the speed of light. So, according to someone inside the train, everything outside has shrunk to a distance of 0 in the direction of motion.

Let's say, now, that the train is moving near, but not quite at, the speed of light. This means that the distance to its destination (wherever that might be) hasn't quite shrunk to 0, but it is a lot closer now than it would be if the train were at rest,
To better illustrate this... say you're in a spaceship travelling to a star named Star (I used this example in the other thread I linked to in my last post). And, let's say Star is 100 light-years away according to an observer on Earth. In your spaceship, you leave Earth and travel towards Star at very near the speed of light. At this near-luminal velocity, if you were to measure the distance between the Earth and Star now, you might find that it's 2 light-years, as opposed to the 100 light-years measured by someone at rest.

Because, according to you, the distance between the Earth and Star has decreased dramatically, it doesn't take you nearly as much time to get to Star. According to an observer on Earth, it would still take you about 100 years to get to Star, travelling at very near the speed of light, but, according to you, it only takes about 2 years.

This is time dilation, and it is caused by length contraction (according to you, the distance between Earth and Star has contracted).
But, there is another side-effect of this. If, according to you, the distance between the Earth and Star has shrunk, you could also say that, instead, you spaceship has gotten longer (this is the opposite of what an external observer would say - they would say that your spaceship is shorter, just as the train from before got shorter - but it's the basis of relativity... it's all relative). The density of your spaceship has stayed the same, but it has gotten longer, so this requires an increase in the mass of the spaceship. This is mass dilation.

If any part of that is unclear, feel free to ask me, and I will do my best to clarify what I can

Originally posted by BLKMJK

Originally posted by chr0naut
reply to post by NightFlight

 

Yes Photons have mass, but only at the speed of light. Their rest mass is zero.

Same goes with some other speed of light particles.

But why is this the case? Photons only have mass at the speed of light but their rest mass is zero? Great, my head will explode when I try to sleep thinking about this.

My illustration above might actually help to answer this (on a rather basic level). Travelling at the speed of light, according to a photon, the distance between itself and anything is 0 - for the photon, space has been reduced to a 0-dimensional point, but, if we want to word it differently, we could just as easily say that the photon occupies all of space at once. Given this, then, we can say that the photon has infinite volume (the volume it needs to occupy all of space at once).

Now, infinity is a concept, not a number, but there is a number (or, rather, an undefined mathematical operation) analogous to infinite: 1/0. If you ask any calculator to find 1/0, some guy will jump out and break your knees. But, if we leave it as 1/0, it is a valid operation identical to the concept of "infinity".
Using this, then, we can say that the volume of the photon is 1/0.

So, the photon has a rest mass of 0. But, moving at the speed of light, it now suddenly has 1/0 volume. What I'm about to do will seem unorthodox to certain people, but bear with me...
The photon had a rest mass of 0 and a rest volume of, let's say, 1. At the speed of light, it has 1/0 volume, so what does that do to the mass? Well... the change in volume is (1/0)/1 = (1/0). So, then, the increase in mass can be said to be (1/0)*0 = 1. Thus, we find that a photon which is massless (0) at rest now has a real mass (1) at the speed of light.

This isn't quite accurate, but it might help to better understand how the photon manages to gain mass at the speed of light. Maybe.