# The Naked Scientists Forum

### Author Topic: How can you tell if your spaceship is standing still in outer space?  (Read 724 times)

#### jerrygg38

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##### How can you tell if your spaceship is standing still in outer space?
« on: 27/08/2016 00:32:07 »
How can you tell if you are standing still in outer space?
You have fancy telescopes in your spaceship and you read the redshift to all the far stars. If they are all balanced equally then it appears that you are standing still. That seems to be one method. Can you make an absolute velocity sensor?  If we moved at very high speeds near 20 percent of the speed of light, no doubt there would be certain non-linearity’s  that could occur. The physical structures within the space ship and the properties of light may make sensors possible. Have any scientists proposed such devices?

#### PhysBang

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #1 on: 27/08/2016 01:53:30 »
You are always free to assume that you are not in motion. It is an arbitrary choice.

#### jerrygg38

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #2 on: 27/08/2016 13:51:58 »
You are always free to assume that you are not in motion. It is an arbitrary choice.
It is not only an arbitrary choice but long ago scientists were threatened with the bonfire if they denied that the Earth was not the center of the universe and everything revolved around it.
If you were traveling at 0.5C all the far stars in front of you would be very blue and all the far stars behind you would be much redder. Since most spaceships travel very slowly you would need very accurate telescopes and computer programs to find your speed compared to the far stars. But that is possible.

#### dlorde

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #3 on: 27/08/2016 14:48:03 »
...Can you make an absolute velocity sensor?
No, because there's no such thing as absolute velocity. All velocities are relative to some frame. For example, you may have zero velocity relative to the Earth, or to the galaxy, etc. Blame Einstein, it's his fault

#### Tim the Plumber

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #4 on: 27/08/2016 16:40:40 »
...Can you make an absolute velocity sensor?
No, because there's no such thing as absolute velocity. All velocities are relative to some frame. For example, you may have zero velocity relative to the Earth, or to the galaxy, etc. Blame Einstein, it's his fault

Galileo Galileo was responsible for this one. Basic relativity. Einstein did the weird stuff about time being relative to something or other....

#### Ethos_

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #5 on: 27/08/2016 17:38:15 »
You are always free to assume that you are not in motion. It is an arbitrary choice.
This is only true if you're not also accelerating or decelerating. In either case, accelerating or decelerating can be registered as changes in inertial forces relative to your personal frame.

#### jeffreyH

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #6 on: 27/08/2016 17:42:13 »
Postulate 1 All velocities are relative.
Postulate 2 There must always be velocities that are faster or slower than the velocity of the local frame.
Postulate 3 Absolute zero velocity cannot be achieved.

#### dlorde

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #7 on: 27/08/2016 19:34:15 »
Postulate 2 There must always be velocities that are faster or slower than the velocity of the local frame.
Faster or slower than the local frame relative to what? If the local frame is stationary relative to, for example, the Earth, there will not be a slower velocity than the local frame, relative to the Earth... There could be faster velocities, but I don't see how that would help for Postulate 3 (shouldn't P3 be the Conclusion?)
« Last Edit: 27/08/2016 19:38:03 by dlorde »

#### jeffreyH

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #8 on: 27/08/2016 20:10:28 »
This should be considered with reference to the number line where positive and negative values for velocity need to be taken into account. If we consider an inertial frame at rest then no direction is preferred so the concept of a slower velocity is undefined. If we choose one direction as preferred then the postulates make sense. This can be an arbitrary choice.

#### syhprum

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #9 on: 27/08/2016 21:02:44 »
the only thing I can think of to which you could measure your relative motion would be the CMBR.
We are not allowed Aether any more.

#### jerrygg38

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #10 on: 28/08/2016 20:04:38 »
...Can you make an absolute velocity sensor?
No, because there's no such thing as absolute velocity. All velocities are relative to some frame. For example, you may have zero velocity relative to the Earth, or to the galaxy, etc. Blame Einstein, it's his fault
Thanks for the laugh. Yes we have an Einsteinian God who appeared before us over a hundred years ago and explained his universe to us. Unfortunately I am a heretic and destined to an anti-Einsteinian world of the dead. Thus I believe in absolute velocity.

#### jerrygg38

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #11 on: 28/08/2016 20:44:57 »
the only thing I can think of to which you could measure your relative motion would be the CMBR.
We are not allowed Aether any more.
What is CMBR? If an object was radiating electromagnetic waves, it would be moving C+V or C-V relative to the bubble of waves. Yet there is no way to measure this. The Aether seems okay to me but it is not stationary. Thus we have moving gravitational fields and moving electromagnetic fields. If the absolute center is where the big bang occurred, everything has an absolute velocity relative to this point. However this point is not on our present universe. To make matters worse, it appears to me that everything is moving at close to the speed of light C with respect to this absolute point. And this does not seem to affect anything within our universe. Then we are left with relativity as the best  fit approximation for the way all the moving fields operate.

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##### Re: How can you tell if your spaceship is standing still in outer space?
« Reply #11 on: 28/08/2016 20:44:57 »