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How to get the speed of my spaceship?

Can a spaceship traveling close to light speed be knocked off course by a gamma ray burst?How to avoid objects when traveling at greater than .75 light speed. or How Not to Go SPLAT?How would an interstellar spaceship's speedometer work if everything else is moving?Practical problems of near-light-speed travelWouldn't a spaceship traveling at luminal or near light speeds come back to find earth hundreds of years in the futureWhich of these two spaceships would count as the fastest man made craft ever launched?Could near light speed ship dilate time severely enough to explore other stars with out breaking the light speed barrier?Can my spaceship figure out its position using Cepheid Variables?Can you catch a spaceship with a train on the Moon?What does the view outside my ship traveling at light speed look like?

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

11

1

$begingroup$

I have a spaceship that can get to speeds very close to the speed of light.

How can this ship measure how fast it is going near the speed of light?

I would think one would measure how fast other stars fly by but does this even work if time dilation makes everything faster outside of my frame?

space space-travel spaceships

share|improve this question

edited Jul 4 at 10:05

L.Dutch♦

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asked Jul 4 at 9:59

sirzentosirzento

5855 bronze badges

$endgroup$

add a comment | 

11

1

$begingroup$

I have a spaceship that can get to speeds very close to the speed of light.

How can this ship measure how fast it is going near the speed of light?

I would think one would measure how fast other stars fly by but does this even work if time dilation makes everything faster outside of my frame?

space space-travel spaceships

share|improve this question

edited Jul 4 at 10:05

L.Dutch♦

103k3232 gold badges248248 silver badges502502 bronze badges

asked Jul 4 at 9:59

sirzentosirzento

5855 bronze badges

$endgroup$

add a comment | 

$begingroup$

I have a spaceship that can get to speeds very close to the speed of light.

How can this ship measure how fast it is going near the speed of light?

I would think one would measure how fast other stars fly by but does this even work if time dilation makes everything faster outside of my frame?

space space-travel spaceships

share|improve this question

edited Jul 4 at 10:05

L.Dutch♦

103k3232 gold badges248248 silver badges502502 bronze badges

asked Jul 4 at 9:59

sirzentosirzento

5855 bronze badges

$endgroup$

share|improve this question

edited Jul 4 at 10:05

L.Dutch♦

103k3232 gold badges248248 silver badges502502 bronze badges

asked Jul 4 at 9:59

sirzentosirzento

5855 bronze badges

share|improve this question

edited Jul 4 at 10:05

L.Dutch♦

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asked Jul 4 at 9:59

sirzentosirzento

5855 bronze badges

edited Jul 4 at 10:05

L.Dutch♦

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edited Jul 4 at 10:05

L.Dutch♦

103k3232 gold badges248248 silver badges502502 bronze badges

asked Jul 4 at 9:59

sirzentosirzento

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asked Jul 4 at 9:59

sirzentosirzento

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2 Answers
2

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oldest

votes

17

$begingroup$

You can use the relativistic Doppler effect

The relativistic Doppler effect is the change in frequency (and wavelength) of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect), when taking into account effects described by the special theory of relativity.

The relativistic Doppler effect is different from the non-relativistic Doppler effect as the equations include the time dilation effect of special relativity and do not involve the medium of propagation as a reference point. They describe the total difference in observed frequencies and possess the required Lorentz symmetry.

Before starting the journey, your ship needs to have a set of reference light sources, with known spectra. During the trip, by measuring those spectra, relative velocity can be calculated.

In the picture below, taken from the linked page, the top half shows what Doppler shift to expect according to the direction in which the observer is looking at the light source in the relativistic case, while the bottom one shows the Doppler shift in the non relativistic case.

share|improve this answer

edited Jul 4 at 13:49

answered Jul 4 at 10:09

L.Dutch♦L.Dutch

103k3232 gold badges248248 silver badges502502 bronze badges

$endgroup$

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  $begingroup$
  Would measuring the doppler shift against the cosmic background radiation work (anywhere in the universe) ?
  $endgroup$
  – Fels
  Jul 4 at 13:32
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @Fels, cosmological subtleties apart, for which I am not able to answer, I am not sure we know its spectrum with the due precision, while we know the emission lines of several species.
  $endgroup$
  – L.Dutch♦
  Jul 4 at 13:48
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  I would think cosmic background radiation, being radiation, would shift like any other radiation. You could measure the doppler shift of external radiation against a light source fixed to your ship. May I propose a space mermaid holding up a lantern on the bow?
  $endgroup$
  – Willk
  Jul 4 at 14:42
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  There is a very slight temperature dipole measured in the CMBR, from which it was calculated that Earth moves at a certain speed relative to the Hubble frame. CMBR should do just fine for relativistic speeds.
  $endgroup$
  – John Dvorak
  Jul 5 at 2:51
  

  
  
  
  

add a comment | 

14

$begingroup$

It is important to note that travelling very near the speed of light is no different from being at rest - it all depends on the chosen frame of reference. Travelling at .999 c in one frame of reference = being totally still in another.

You can only measure your speed relative to other objects in space. There is no absolute speed. If you are heading towards a star, you can measure your speed relative to that star by the blueshift of the star's spectrum (which has a special signature depending on spectral type). Similarly, if you are moving away from a star, you can measure the redshift of its spectrum.

If you aren't heading directly away from or towards a star, you can measure the redshift and blueshift of stars to the side and compensate for the angle.

share|improve this answer

answered Jul 4 at 10:19

Klaus Æ. MogensenKlaus Æ. Mogensen

4,50511 gold badge77 silver badges2020 bronze badges

$endgroup$

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  This is false due to cosmic background radiation.
  $endgroup$
  – TLW
  Jul 5 at 1:54
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @TLW: How does cosmic background radiation make this false?
  $endgroup$
  – Klaus Æ. Mogensen
  Jul 5 at 7:19
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @TLW cosmic background radiation gives a convenient reference frame, but it is not "absolute rest". See physics.stackexchange.com/questions/25928/…
  $endgroup$
  – MaudPieTheRocktorate
  Jul 5 at 11:33
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @KlausÆ.Mogensen - "travelling very near the speed of light is no different from being at rest" -> This is false in the universe due to CMB. The faster you travel relative to the CMB rest frame, the more CMB you intercept.
  $endgroup$
  – TLW
  Jul 6 at 1:35
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @MaudPieTheRocktorate - I make no claims that it is absolute rest. However, it is a universally-defined reference frame in our universe.
  $endgroup$
  – TLW
  Jul 6 at 1:36
  

  
  
  
  

add a comment | 

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17

$begingroup$

You can use the relativistic Doppler effect

The relativistic Doppler effect is the change in frequency (and wavelength) of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect), when taking into account effects described by the special theory of relativity.

The relativistic Doppler effect is different from the non-relativistic Doppler effect as the equations include the time dilation effect of special relativity and do not involve the medium of propagation as a reference point. They describe the total difference in observed frequencies and possess the required Lorentz symmetry.

Before starting the journey, your ship needs to have a set of reference light sources, with known spectra. During the trip, by measuring those spectra, relative velocity can be calculated.

In the picture below, taken from the linked page, the top half shows what Doppler shift to expect according to the direction in which the observer is looking at the light source in the relativistic case, while the bottom one shows the Doppler shift in the non relativistic case.

share|improve this answer

edited Jul 4 at 13:49

answered Jul 4 at 10:09

L.Dutch♦L.Dutch

103k3232 gold badges248248 silver badges502502 bronze badges

$endgroup$

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  $begingroup$
  Would measuring the doppler shift against the cosmic background radiation work (anywhere in the universe) ?
  $endgroup$
  – Fels
  Jul 4 at 13:32
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @Fels, cosmological subtleties apart, for which I am not able to answer, I am not sure we know its spectrum with the due precision, while we know the emission lines of several species.
  $endgroup$
  – L.Dutch♦
  Jul 4 at 13:48
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  I would think cosmic background radiation, being radiation, would shift like any other radiation. You could measure the doppler shift of external radiation against a light source fixed to your ship. May I propose a space mermaid holding up a lantern on the bow?
  $endgroup$
  – Willk
  Jul 4 at 14:42
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  There is a very slight temperature dipole measured in the CMBR, from which it was calculated that Earth moves at a certain speed relative to the Hubble frame. CMBR should do just fine for relativistic speeds.
  $endgroup$
  – John Dvorak
  Jul 5 at 2:51
  

  
  
  
  

add a comment | 

17

$begingroup$

You can use the relativistic Doppler effect

The relativistic Doppler effect is the change in frequency (and wavelength) of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect), when taking into account effects described by the special theory of relativity.

The relativistic Doppler effect is different from the non-relativistic Doppler effect as the equations include the time dilation effect of special relativity and do not involve the medium of propagation as a reference point. They describe the total difference in observed frequencies and possess the required Lorentz symmetry.

Before starting the journey, your ship needs to have a set of reference light sources, with known spectra. During the trip, by measuring those spectra, relative velocity can be calculated.

In the picture below, taken from the linked page, the top half shows what Doppler shift to expect according to the direction in which the observer is looking at the light source in the relativistic case, while the bottom one shows the Doppler shift in the non relativistic case.

share|improve this answer

edited Jul 4 at 13:49

answered Jul 4 at 10:09

L.Dutch♦L.Dutch

103k3232 gold badges248248 silver badges502502 bronze badges

$endgroup$

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  $begingroup$
  Would measuring the doppler shift against the cosmic background radiation work (anywhere in the universe) ?
  $endgroup$
  – Fels
  Jul 4 at 13:32
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @Fels, cosmological subtleties apart, for which I am not able to answer, I am not sure we know its spectrum with the due precision, while we know the emission lines of several species.
  $endgroup$
  – L.Dutch♦
  Jul 4 at 13:48
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  I would think cosmic background radiation, being radiation, would shift like any other radiation. You could measure the doppler shift of external radiation against a light source fixed to your ship. May I propose a space mermaid holding up a lantern on the bow?
  $endgroup$
  – Willk
  Jul 4 at 14:42
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  There is a very slight temperature dipole measured in the CMBR, from which it was calculated that Earth moves at a certain speed relative to the Hubble frame. CMBR should do just fine for relativistic speeds.
  $endgroup$
  – John Dvorak
  Jul 5 at 2:51
  

  
  
  
  

add a comment | 

$begingroup$

You can use the relativistic Doppler effect

The relativistic Doppler effect is the change in frequency (and wavelength) of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect), when taking into account effects described by the special theory of relativity.

The relativistic Doppler effect is different from the non-relativistic Doppler effect as the equations include the time dilation effect of special relativity and do not involve the medium of propagation as a reference point. They describe the total difference in observed frequencies and possess the required Lorentz symmetry.

Before starting the journey, your ship needs to have a set of reference light sources, with known spectra. During the trip, by measuring those spectra, relative velocity can be calculated.

In the picture below, taken from the linked page, the top half shows what Doppler shift to expect according to the direction in which the observer is looking at the light source in the relativistic case, while the bottom one shows the Doppler shift in the non relativistic case.

share|improve this answer

edited Jul 4 at 13:49

answered Jul 4 at 10:09

L.Dutch♦L.Dutch

103k3232 gold badges248248 silver badges502502 bronze badges

$endgroup$

share|improve this answer

edited Jul 4 at 13:49

answered Jul 4 at 10:09

L.Dutch♦L.Dutch

103k3232 gold badges248248 silver badges502502 bronze badges

answered Jul 4 at 10:09

L.Dutch♦L.Dutch

103k3232 gold badges248248 silver badges502502 bronze badges

answered Jul 4 at 10:09

L.Dutch♦L.Dutch

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14

$begingroup$

It is important to note that travelling very near the speed of light is no different from being at rest - it all depends on the chosen frame of reference. Travelling at .999 c in one frame of reference = being totally still in another.

You can only measure your speed relative to other objects in space. There is no absolute speed. If you are heading towards a star, you can measure your speed relative to that star by the blueshift of the star's spectrum (which has a special signature depending on spectral type). Similarly, if you are moving away from a star, you can measure the redshift of its spectrum.

If you aren't heading directly away from or towards a star, you can measure the redshift and blueshift of stars to the side and compensate for the angle.

share|improve this answer

answered Jul 4 at 10:19

Klaus Æ. MogensenKlaus Æ. Mogensen

4,50511 gold badge77 silver badges2020 bronze badges

$endgroup$

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  This is false due to cosmic background radiation.
  $endgroup$
  – TLW
  Jul 5 at 1:54
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @TLW: How does cosmic background radiation make this false?
  $endgroup$
  – Klaus Æ. Mogensen
  Jul 5 at 7:19
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @TLW cosmic background radiation gives a convenient reference frame, but it is not "absolute rest". See physics.stackexchange.com/questions/25928/…
  $endgroup$
  – MaudPieTheRocktorate
  Jul 5 at 11:33
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @KlausÆ.Mogensen - "travelling very near the speed of light is no different from being at rest" -> This is false in the universe due to CMB. The faster you travel relative to the CMB rest frame, the more CMB you intercept.
  $endgroup$
  – TLW
  Jul 6 at 1:35
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @MaudPieTheRocktorate - I make no claims that it is absolute rest. However, it is a universally-defined reference frame in our universe.
  $endgroup$
  – TLW
  Jul 6 at 1:36
  

  
  
  
  

add a comment | 

14

$begingroup$

It is important to note that travelling very near the speed of light is no different from being at rest - it all depends on the chosen frame of reference. Travelling at .999 c in one frame of reference = being totally still in another.

You can only measure your speed relative to other objects in space. There is no absolute speed. If you are heading towards a star, you can measure your speed relative to that star by the blueshift of the star's spectrum (which has a special signature depending on spectral type). Similarly, if you are moving away from a star, you can measure the redshift of its spectrum.

If you aren't heading directly away from or towards a star, you can measure the redshift and blueshift of stars to the side and compensate for the angle.

share|improve this answer

answered Jul 4 at 10:19

Klaus Æ. MogensenKlaus Æ. Mogensen

4,50511 gold badge77 silver badges2020 bronze badges

$endgroup$

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  This is false due to cosmic background radiation.
  $endgroup$
  – TLW
  Jul 5 at 1:54
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @TLW: How does cosmic background radiation make this false?
  $endgroup$
  – Klaus Æ. Mogensen
  Jul 5 at 7:19
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @TLW cosmic background radiation gives a convenient reference frame, but it is not "absolute rest". See physics.stackexchange.com/questions/25928/…
  $endgroup$
  – MaudPieTheRocktorate
  Jul 5 at 11:33
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @KlausÆ.Mogensen - "travelling very near the speed of light is no different from being at rest" -> This is false in the universe due to CMB. The faster you travel relative to the CMB rest frame, the more CMB you intercept.
  $endgroup$
  – TLW
  Jul 6 at 1:35
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @MaudPieTheRocktorate - I make no claims that it is absolute rest. However, it is a universally-defined reference frame in our universe.
  $endgroup$
  – TLW
  Jul 6 at 1:36
  

  
  
  
  

add a comment | 

$begingroup$

It is important to note that travelling very near the speed of light is no different from being at rest - it all depends on the chosen frame of reference. Travelling at .999 c in one frame of reference = being totally still in another.

You can only measure your speed relative to other objects in space. There is no absolute speed. If you are heading towards a star, you can measure your speed relative to that star by the blueshift of the star's spectrum (which has a special signature depending on spectral type). Similarly, if you are moving away from a star, you can measure the redshift of its spectrum.

If you aren't heading directly away from or towards a star, you can measure the redshift and blueshift of stars to the side and compensate for the angle.

share|improve this answer

answered Jul 4 at 10:19

Klaus Æ. MogensenKlaus Æ. Mogensen

4,50511 gold badge77 silver badges2020 bronze badges

$endgroup$

share|improve this answer

answered Jul 4 at 10:19

Klaus Æ. MogensenKlaus Æ. Mogensen

4,50511 gold badge77 silver badges2020 bronze badges

answered Jul 4 at 10:19

Klaus Æ. MogensenKlaus Æ. Mogensen

4,50511 gold badge77 silver badges2020 bronze badges

answered Jul 4 at 10:19

Klaus Æ. MogensenKlaus Æ. Mogensen

4,50511 gold badge77 silver badges2020 bronze badges