# Why can't u go faster than the speed of light when speed doesn't exist

If you are the only object in the universe, what speed are you going?

Well there would be no such thing as speed because your speed is only relative to other objects. So if there is no such thing as speed, how is there a speed limit?

Let me give an example.

If you take off from earth in a really fast rocket to visit another planet, when you come back, you will have aged less than everyone on earth because time slowed down for you.

But how did you go faster than the people of earth when its all relative?
You simple got father away from the people of earth, then you got closer to the people of earth. Who is to say if your rocket moved or the earth moved. There is no difference.

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ghwellsjr
Gold Member
Let's go back to your original idea of you being the only object in the universe and you fire your rocket. Your rockect will leave an exhaust and now you are no longer the only object in the universe. You can consider your motion relative to the exhaust, can't you?

If you are all alone, there may not be anything to define inertial vs non-inertial and so c. Interesting here that we can't really use relativity to make sense out of such a hypothetical place.

What is the mass of the universe? What is the mass of the observable universe? Does a closed universe have a mass?

None of the above questions have answers. We know the density of the universe (at least in our local area), but we can only speculate on the extent of the universe, making it impossible for us to give a definitive answer for the mass of the universe. We cannot answer the second question, either. Since the observable universe isn't asymptotically flat, nor is it stationary, and since it may not be an isolated system, none of our definitions of mass in General Relativity apply, and there is no way to calculate the mass of the observable universe. The answer to the third question is also no : the following quote from (Misner, et al., pg 457) explains why:

"There is no such thing as the energy (or angular momentum, or charge) of a closed universe, according to general relativity, and this for a simple reason. To weigh something one needs a platform on which to stand to do the weighing ...

"To determine the electric charge of a body, one surrounds it by a large sphere, evaluates the electric field normal to the surface at each point on this sphere, integrates over the sphere, and applies the theorem of Gauss. But within any closed model universe with the topology of a 3-sphere, a Gaussian 2-sphere that is expanded widely enough from one point finds itself collapsing to nothingness at the antipodal point. Also collapsed to nothingness is the attempt to acquire useful information about the "charge of the universe": the charge is trivially zero."
- http://en.wikipedia.org/wiki/Mass_in_general_relativity

Who is to say if your rocket moved or the earth moved. There is no difference.
The difference is that the rocket accelerated and then decelerated upon return....THAT distinguishes between the two motions....accelerated motion is different from inertial [non accelerated] motion.

If you are all alone, there may not be anything to define inertial vs non-inertial..
Sure there is, you'll FEEL non inertial motion just as you do when you accelerate in a car.

The difference is that the rocket accelerated and then decelerated upon return....THAT distinguishes between the two motions....accelerated motion is different from inertial [non accelerated] motion.

Sure there is, you'll FEEL non inertial motion just as you do when you accelerate in a car.
Something *like* Mach's principle may be responsible for inertia... in the empty pocket universe there might not be anything to supply something like that...

oh. I guess the rest of the OP is unrelated to the first question. never mind.

if there's just the Earth, and a rocket, and nothing else in the universe, and that is somehow possible, then it's not clear if / how the aging / acceleration business would work.

Dale
Mentor
If you are the only object in the universe, what speed are you going?
When you gain access to such a universe and make said measurements and publish those measurements in a reputable journal then we can discuss them here. Until then it is pure speculation.

You are welcome to re-post the non-speculative portions of your post in a new thread.