# A spaceship moving near the speed of light

A spaceship moves near the speed of light. Its time becomes slow for an observer on earth.

1. Does 'time' slow only in and around ( i.e. the space inside and outside) the spaceship? If yes, to what extent ( i.e. how much meters or centimeters) above the physical boundary of spaceship.

2. Suppose, the space ship has something vertically projected from it ( a thin antenna etc.) that reaches a height of 100 km (or even 100000000.......km, just suppose). There is a watch at top of this antenna.

a) Would it also slow down?

b) Would all the space between bottom to top of this antenna experience slowing of time, as seen by an observer on earth?

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ghwellsjr
Gold Member
A spaceship moves near the speed of light. Its time becomes slow for an observer on earth.

1. Does 'time' slow only in and around ( i.e. the space inside and outside) the spaceship? If yes, to what extent ( i.e. how much meters or centimeters) above the physical boundary of spaceship.

2. Suppose, the space ship has something vertically projected from it ( a thin antenna etc.) that reaches a height of 100 km (or even 100000000.......km, just suppose). There is a watch at top of this antenna.

a) Would it also slow down?

b) Would all the space between bottom to top of this antenna experience slowing of time, as seen by an observer on earth?
Time for everything that is moving in the earth rest frame is dilated. It's as simple as that.

HallsofIvy
Homework Helper
A spaceship moves near the speed of light. Its time becomes slow for an observer on earth.

1. Does 'time' slow only in and around ( i.e. the space inside and outside) the spaceship? If yes, to what extent ( i.e. how much meters or centimeters) above the physical boundary of spaceship.

2. Suppose, the space ship has something vertically projected from it ( a thin antenna etc.) that reaches a height of 100 km (or even 100000000.......km, just suppose). There is a watch at top of this antenna.

a) Would it also slow down?

b) Would all the space between bottom to top of this antenna experience slowing of time, as seen by an observer on earth?
Any thing that is moving near the speed of light, relative to an observer, will be moving slower compared to that observer. It has nothing to do with distance.

Any thing that is moving near the speed of light, relative to an observer, will be moving slower compared to that observer. It has nothing to do with distance.
Suppose the air ship is hollow from inside and is air tight ( or there is vacuum inside it).

Can we say that now 'space' itself is moving slower compared to the observer?

ghwellsjr
Gold Member
Suppose the air ship is hollow from inside and is air tight ( or there is vacuum inside it).

Can we say that now 'space' itself is moving slower compared to the observer?
If there is air in the ship, then each atom and molecule will be time dilated according to the earth frame.

What is the meaning of empty space moving?

If there is air in the ship, then each atom and molecule will be time dilated according to the earth frame.

What is the meaning of empty space moving?
I heard a scientist saying on the discovery channel, ' This universe is not expanding into empty space, it is creating 'space' while it expands.'

So anything which is created can be called a 'thing' ( a noun).

So, I was talking about this space-thing (inside the spaceship) to be moving slower as compared to earth.

I hope I don't sound ripe for an asylum.

ghwellsjr
Gold Member
I heard a scientist saying on the discovery channel, ' This universe is not expanding into empty space, it is creating 'space' while it expands.'

So anything which is created can be called a 'thing' ( a noun).

So, I was talking about this space-thing (inside the spaceship) to be moving slower as compared to earth.

I hope I don't sound ripe for an asylum.
I think the scientist was trying to point out that without matter, there is no meaning to empty space.

I think the scientist was trying to point out that without matter, there is no meaning to empty space.
when space is said to have quantum fluctuations, why can't it be called a 'thing'?

ghwellsjr
Gold Member
when space is said to have quantum fluctuations, why can't it be called a 'thing'?
You're on the wrong forum for questions like that.

The only sense in which empty space can have time associated with it is with regard to the coordinate time defined by a given Inertial Reference Frame (IRF) and there is no motion associated with any coordinate time. So in the earth's IRF, the spaceship's time is dilated but the coordinate time for the region of empty space inside the spaceship is not time dilated. Time Dilation is the ratio of the time a moving clock (or anything) accumulates to the accumulation of coordinate time. The speed of each item with respect to the chosen IRF determines its Time Dilation. If different things have different speeds, they will have different Time Dilations.

So if there are molecules inside the hollow ship and they are traveling at different speeds, each individual molecule will have its own different Time Dilation. How would you identify the speed of the space between the different molecules?

I don't know how to communicate the concept to you any more clearly than that. It seems that you'd like this thread to go in some direction but I have no idea what you're looking for. Time Dilation is a very simple concept as I said in my first post. I don't know why you want to make it complicated.

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You're on the wrong forum for questions like that.

The only sense in which empty space can have time associated with it is with regard to the coordinate time defined by a given Inertial Reference Frame (IRF) and there is no motion associated with any coordinate time. So in the earth's IRF, the spaceship's time is dilated but the coordinate time for the region of empty space inside the spaceship is not time dilated. Time Dilation is the ratio of the time a moving clock (or anything) accumulates to the accumulation of coordinate time. The speed of each item with respect to the chosen IRF determines its Time Dilation. If different things have different speeds, they will have different Time Dilations.

So if there are molecules inside the hollow ship and they are traveling at different speeds, each individual molecule will have its own different Time Dilation. How would you identify the speed of the space between the different molecules?

I don't know how to communicate the concept to you any more clearly than that. It seems that you'd like this thread to go in some direction but I have no idea what you're looking for. Time Dilation is a very simple concept as I said in my first post. I don't know why you want to make it complicated.
I can't make anything complicated.

I just want to say that the quantum fluctuations of the space 'inside' the spaceship will also slow down ( if they are visible/detectable at all!)

Time does not get slowed down. It is just a matter of perspective, point of view effect. All processes 'seem' to go slower when they seem to be moving, and seem faster when they seem stationary. Clocks on the ship seem slower, but to the people on board clocks on earth seem slower. There is no actual absolute objective slowing down of anything.

ghwellsjr