Gravitational Redshift of a laser

  • #1
Torog
53
1
If we run two identical lasers and put one at sea level and one on top of a high mountain, will they operate at different frequencies?
 

Answers and Replies

  • #2
Drakkith
Staff Emeritus
Science Advisor
2022 Award
22,245
6,319
They might depending on what altitude you're measuring their respective frequencies from. Measuring at an altitude different from the altitude of the respective laser will produce a red/blueshift. Measuring the frequency of the mountain laser from sea level will produce a blueshift, and measuring the frequency of the sea level laser from a higher altitude will produce a redshift.
 
  • #3
33,653
11,218
If we run two identical lasers and put one at sea level and one on top of a high mountain, will they operate at different frequencies?
Adding on to what @Drakkith said, if you measure their frequencies with identical local clocks they will read the same.
 
  • #4
Torog
53
1
What if I use the lasers as clocks - measure the pulses, divide many times and put the data to a readout. Shouldn't the clock (laser) on the mountain be slower?

I do understand that light as it falls into a gravitational field it gains energy and moves to blue and the opposite happens as light has to work its way out of a gravitational field.
 
  • #5
33,653
11,218
Shouldn't the clock (laser) on the mountain be slower?
All of the above still applies. It will be slower than normal for any clock above it, faster for any clock below it, and unaltered for a clock right next to it.
 
  • #6
Torog
53
1
Excuse me if I shift to cosmology. From what I understand the observed red shift of stars should come from three factors - according to the present model - First is a red shift given by the recession velocity (or general expansion of the Universe) second by the red shift caused by light having to make its way out of the gravitational field and third by the light having come from a star, quasar or other with a strong gravitational field where time and chemical processes run slower (redder) due to time being slower in the heavy gravitational field.
 
  • #7
33,653
11,218
First is a red shift given by the recession velocity (or general expansion of the Universe) second by the red shift caused by light having to make its way out of the gravitational field and third by the light having come from a star, quasar or other with a strong gravitational field where time and chemical processes run slower (redder) due to time being slower in the heavy gravitational field.
The second and third are the same.
 
  • #8
jartsa
1,563
134
Excuse me if I shift to cosmology. From what I understand the observed red shift of stars should come from three factors - according to the present model - First is a red shift given by the recession velocity (or general expansion of the Universe) second by the red shift caused by light having to make its way out of the gravitational field and third by the light having come from a star, quasar or other with a strong gravitational field where time and chemical processes run slower (redder) due to time being slower in the heavy gravitational field.


We can combine redshift and gravitational time dilation like this:

$$ totalRedshift = \sqrt {redshift * gravitationalTimeDilation } $$

Or like this:

$$ totalRedshift = 0 * redshift + gravitationalTimeDilation $$

Or like this:

$$ totalRedshift = redshift + 0 * gravitationalTimeDilation $$


That's a joke or something. But if we calculate the redshift factor and the gravitational time dilation factor, we always get the same number. So the formulas are correct, in a way.
 
Last edited:

Suggested for: Gravitational Redshift of a laser

Replies
27
Views
840
  • Last Post
Replies
6
Views
687
  • Last Post
Replies
5
Views
562
Replies
3
Views
720
Replies
15
Views
1K
  • Last Post
Replies
15
Views
1K
Replies
7
Views
418
Replies
10
Views
656
  • Last Post
Replies
4
Views
1K
Replies
4
Views
400
Top