# Space-time fabric distortion measuring

1. Feb 9, 2010

### steli

Hi, I have a question about a fact that I did't understand, and all the world takes this as it is: How can the space-time distortion, generated by gravitational waves, can be measured? All scientist say that the space is stretched and squeezed, but how much means that, because 1 meter stretched is equal with 1 meter squeezed. I saw a documentary on youtube that said if a collision between 2 neutron stars near Earth (theoretically), will generate gravitational waves that will destroy the Earth. How? at atomic level, breaking the bond between atoms..., this means that the strong and weak nuclear forces or electromagnetic forces are independent from space-time fabric?
Thanks.

2. Feb 9, 2010

### Ich

But a meterstick stretched may be 1.20 m, and have a problem.
For gravitational waves: if you measure the distance between two freely floating points as a GW goes through, you'll find the distance to be 1.20 m in one millisecond, 80 cm in the next, and so on. That's not a problem, as this distance variation comes without acceleration and thus without any forces. It's the "natural state" of the two points.
It becomes a problem, though, if the points are connected by something rigid, like a steel bar. Steel bars don't want to be 1.20 m long in one ms, and 80 cm in the next. Internal forces will try to keep it at a constant length, accelerating the individual parts away from their "natural" position. These forces could break it. (Theoretically, with very weak steel and very fat neutron stars)

3. Feb 9, 2010

### steli

But how can you measure the meterstick when the gravity wave passes it.
So you say that the space-time distortion does affect the atomic forces. This could make sense and can explain the stress at atomic level.
At least that I understand.
Thanks.

4. Feb 9, 2010

### Ich

There are two possibilities:
1) you take a "meterstick" and listen to its vibrations. If a gravitational wave passes through it, the internal forces will make it start ringing. You can measure that, in principle,
2) You take those freely floating points (mirrors) and measure their distance with a laser beam.
In both cases, what's important is that bound (coherent) objects don't simply follow the changing distances, but instead at least try to stay as they are.

5. Feb 9, 2010

### Matterwave

Currently, the method to try to detect gravity waves involve laser interferometry. The largest gravity wave detector, LIGO is basically a GIANT laser interferometry lab.

The lasers are several kilometers long and situated perpendicular to each other. They are made to interfere with each other at some point and you get an interference pattern. If a gravity wave passes by, it shrinks or expands (the wavelength of) ONE of the lasers a tiny bit (nano meter scale), and it doesn't affect the other laser. This changes the interference pattern, and that's how you see the gravity wave.

6. Feb 10, 2010

### Chronos

LIGO is the short answer, as matterwave noted. By 2020 an even more sophisticated instrument is planned to be deployed. It is called LISA.