But why can't i travel faster than the speed of light?

Question

I'm laying in my bed right now. Am I traveling 0mph? Am I traveling 850-ish mph (south texas) as the earth rotates? Am I traveling 67,000mph as my planet orbits the sun? Am I traveling 560,000mph as our sun orbits the galaxy? What speed is our galaxy moving at as it travels through the universe? Point is, velocity requires relativity to a point in space, or relativity to an object which has a location.

I'm not saying that Einstein's theory of general or special relativity is flawed. I'm not claiming to be smarter than Einstein. I'm claiming that nobody has succeeded in clarifying this point to me and it keeps me up. I've spent so much time in my life trying to conceptualize this

How can we determine that it is impossible to travel faster than the speed of light if there is no universal point of origin in our universe from which all velocity is measured relative to? Wouldn't general relativity be more about observer perception?

I'm orbiting the center of the galaxy at 560k mph. If I shine a light in the same direction that I am orbiting why wouldn't the speed of that ray of light be c + 560,000 mph relative to the center of the galaxy?

Imagine hypothetically that I am on a spacecraft in the middle of open space, in between galaxies where no bodies of mass can affect my spacecraft with gravitationalpull. If I begin traveling from a certain location at 99.9% of c, why couldn't I fire the rocket up again to accelerate to 110% of c from that original location? What... is space a medium that prohibits this, or is my spacecraft just aware of Einstein's theory and doesn't want to break any rules?... my old physics professor who i refer to as an "information regurgitator" basically would tell me to just accept it and don't ask questions in a nutshell. He said that my spacecraft would not experience time if it was traveling at the speed of light. That does not pass through my mental filter. In my mind the spacecraft would experience time no different than anything else, it only wouldn't experience time RELATIVE to it's original location that it left from in the first place. The location that the spacecraft's velocity is relative to

I'm not looking for somebody to point out the mathematical demonstrations to me. Even when I do them myself they still don't clearly reveal the intuition behind this concept. I think most people do not totally understand general relativity because none of them have been able to decisively explain this to me

Answer 1

How can we determine that it is impossible to travel faster than the speed of light if there is no universal point of origin in our universe from which all velocity is measured relative to? Wouldn't general relativity be more about observer perception?

You're thinking in terms of classical mechanics and missing the relativity part here. What you are saying is true in terms of classical mechanics, but classical mechanics does not set a speed limit so the model is inapplicable in relativistic speed regimes. A speed limit in classical mechanics is like redlining your car: You just can't go faster. That's it. Nothing else changes with speed. There are no additional effects added to the classical model. Most notably, if the lamp was moving away from you, you still would measure a slower speed just like every other thing because that still adheres to not breaking the maximum speed limit. Your question would hold if the speed of light in empty space could be measured lower, but never higher.

But relativity it isn't just about a speed limit. It's about an invariant speed. Of course, it also includes "other effects" like time dilation. Remember, light has been measured to travel the same speed in empty space regardless of relative motion. It cannot be sped up or slowed down. If you measure the speed of light and it is always the same regardless of relative motion then you do not need an absolute spatial reference because all measurements read the same anyways. Think less about about max speed and more about the speed being measured always being the same.

Answer 2

The relativistic "speed limit" is true in every intertial reference frame. No matter whether measured with respect to the planet, sun, galaxy, or any other valid (*; see footnote) frame, no matter can move at a speed greater than c. This is reflected in the relativistic addition of velocities principle: if you shoot a flashlight at .999c, you still see the beam it emits traveling at c.

(*) Obviously, you can design an inertial frame that travels at a relative speed of greater than c with respect to Earth -- and by extension with respect to all matter in the universe -- but that's not a valid inertial frame. If I recall, such frames do pop up as a mathematical convenience in astronomy (related to projecting 3D paths onto the sphere).

Answer 3

Apparently Einstein recieved some angry letters from upset people who accused him of setting a speed limit to the universe and so exploding their dreams of interstellar space travel fed by SF.

The 'speed limit' is a limit set by nature and not by Einstein - he merely discovered it. It's been verified experimentally, and is a foundation stone in constructing physical theories.

It was pointed out by Maxwell's equations for electromagnetism that showed that the speed of light was absolute. At the time this wasn't taken seriously. But Einstein did.

Answer 4

Because in special relativity there's this expression $\gamma$, known as the Lorentz factor, that breaks once you get close to the speed of light.

$\gamma \equiv \frac{1}{\sqrt{1-v^2/c^2}}$

Here $c$ is the speed of light and $v$ is your current speed.

$\gamma$ shows up everywhere in special relativity (in fact if you're doing a physics exam and you see it, you know you need to use special relativity on the question). You can see that once your speed $v$ approaches $c$, then $\gamma$ becomes arbitrarily large. This breaks a lot of things, such as the expression for kinetic energy ($KE = (\gamma -1) mc^2$).

Answer 5

The basic reason that you cannot travel faster than light is that you have mass. The relationship between mass, energy, and momentum is $$m^2 c^2 = E^2/c^2 - p^2$$ This can be expressed in terms of velocity with the substitution $v/c=cp/E$. This gives the velocity in terms of energy as $$v=\frac{\sqrt{E^2-m^2c^4}}{E}c$$ which goes to $c$ as $E$ goes to infinity for any $m\ne0$

For $m=0$ the expression simplifies to $v=c$ regardless of $E$.