Gravitational Wave Stretching: LIGO Arm vs Light

In summary, the conversation discusses the concept of light and matter being affected differently by the stretching of space. While a gravitational wave can stretch the LIGO arm, it does not affect the light within it. This is puzzling because the red shift of a distant galaxy, which is caused by the expansion of space, suggests that light should also be stretched. Some have questioned this and it is even addressed on the LIGO FAQ list. The detection of gravitational waves is done indirectly by measuring the slight changes in the length of the LIGO arm caused by the fluidity of spacetime.
  • #1
Alfred Cann
82
4
I'm puzzled that the stretching of space by a gravitational wave stretches the LIGO arm but not the light within it. Because we are told that the red shift of a distant galaxy is caused by light being stretched by the expansion of space (the universe).
 
Astronomy news on Phys.org
  • #2
Alfred Cann said:
I'm puzzled that the stretching of space by a gravitational wave stretches the LIGO arm but not the light within it.
It might be worth investigating the magnitude difference between light and matter... I'm going to now. :-p
Alfred Cann said:
Because we are told that the red shift of a distant galaxy is caused by light being stretched by the expansion of space (the universe).
Such a small amount over a very long time...
 
  • #3
Alfred Cann said:
I'm puzzled that the stretching of space by a gravitational wave stretches the LIGO arm but not the light within it. Because we are told that the red shift of a distant galaxy is caused by light being stretched by the expansion of space (the universe).

Many people have asked this question, in fact it is even on the LIGO FAQ list:

http://ligo.org/science/faq.php
 
  • Like
Likes Dirickby
  • #4
phyzguy said:
It was worth posting again, my favorite:
faq-aligo-reach.png

I wish I could get it on google maps and point it the way I'm facing...
 

Attachments

  • faq-aligo-reach.png
    faq-aligo-reach.png
    102 KB · Views: 635
Last edited:
  • #6
If I remember correctly, LIGO does not detect changes in the wavelength of its beams directly but by inferring it from how far out of phase two different lasers become.

When they leave, the beams are perfectly in sync, when they come back, any deviation from that is from the fluidity of spacetime.

This is because it spent less time in one arm than the other because it got slightly longer or shorter as the wave passed. That’s why it can be detected from within the wave itself.
 

1. What are gravitational waves?

Gravitational waves are ripples in the fabric of space-time caused by the acceleration of massive objects, such as colliding black holes or neutron stars.

2. How are gravitational waves detected?

Gravitational waves are detected using highly sensitive instruments called interferometers, such as the Laser Interferometer Gravitational-Wave Observatory (LIGO). These instruments measure tiny changes in the length of two perpendicular arms caused by passing gravitational waves.

3. What is the difference between LIGO arm stretching and light stretching?

LIGO arm stretching refers to the physical lengthening of the arms of the interferometer caused by the passing gravitational waves. Light stretching refers to the stretching of the wavelength of light as it travels through space-time affected by gravitational waves.

4. Why do gravitational waves cause stretching?

Gravitational waves cause stretching because they create tiny changes in the curvature of space-time. As the waves pass through an object, it is pulled and stretched in one direction and compressed in the other, causing the object to appear longer in one direction and shorter in the other.

5. What can we learn from gravitational wave stretching?

Gravitational wave stretching can provide valuable information about the source of the waves, such as the mass and location of the objects that created them. It can also help us better understand the nature of gravity and the behavior of space-time.

Similar threads

Replies
12
Views
1K
  • Astronomy and Astrophysics
Replies
7
Views
2K
  • Special and General Relativity
Replies
2
Views
697
  • Astronomy and Astrophysics
Replies
4
Views
1K
  • Special and General Relativity
Replies
12
Views
1K
  • Other Physics Topics
Replies
27
Views
1K
  • Astronomy and Astrophysics
Replies
11
Views
3K
  • Astronomy and Astrophysics
Replies
2
Views
1K
  • Astronomy and Astrophysics
Replies
10
Views
2K
  • Special and General Relativity
Replies
11
Views
2K
Back
Top