Why does the LIGO, the gravitational-wave observatory work? In an earlier thought , there was an argument against the used method. One ...
Why does the LIGO, the gravitational-wave observatory work? In an earlier thought, there was an argument against the used method.
One part of the query about the method was based on the consideration, that if space stretches, everything stretches with it what is not bounded by local forces. Light does not bind by local forces, ergo its waves must stretch too, so keeping their phase same at the meeting point, hence could not produce the change of the interference pattern what the LIGO experiment was built on.
There is a supporting argument for the LIGO method also. Because the light speed is constant in the vacuum, if space stretches and the distances become different, the light needs different time to take different distances. The two perpendicular LIGO arms stretch differently by the gravitational waves, so the two light paths change their lengths, ergo the time needed to take the perpendicular LIGO arms by the light by its constant speed changes, so the two light rays meet in different phases at the meeting point as it was before the stretch, hence the interference pattern changes. So, the method of the LIGO experiment works.
The LIGO supporting argument seems right. If the length of one of the arms becomes longer by the stretch of the gravitational wave, the light would need a longer time to take the longer distance. Otherwise, it would need to travel faster than the speed of light to take it by the same time to keep the interference pattern unchanged. And if the length of an arm becomes shorter by the stretch of the gravitational wave, the light would need a shorter time to take the shorter distance. Otherwise, it would need to travel slower than the speed of light to take it by the same time to keep the interference pattern intact. Both scenarios are impossible. The light speed in the vacuum is fixed, cannot be different, hence the interference pattern must change.
However, the querying argument seems right also. The gravitational waves stretch and contract the space with the light wave as well, and with accordion with each other. If space could change differently contrary to how the light wave changes by the effect of the gravitational waves, it would mean that the light wave is held together by local forces, or it is not attached to space. Observations show that the light wave becomes longer as space expands. We see it in the expansion of the universe by the wavelength increase of the universe's background radiation. It suggests that the light wave is not held together by local forces, and it proves that the light wave is attached to space. We might use the rubber sheet model for this scenario. A rubber sheet represents the space and crossing wavy lines drawn on the sheet represents the space-attached light waves. As we stretch and compress the rubber sheet, we cannot make the waves cross each other in different phases. The whole drawn wavy pattern remains intact, only the waves stretch or contract. This approach suggests that the phase of the light waves remains unchanged, the interference pattern would not change but remain the same.
The two seemingly valid arguments are controversial to each other. The fact is that the LIGO experiment shows interference pattern changes consistent with the theoretical calculations of how the gravitational waves stretch the space when the neutron stars or black holes collide. Also, we can see wavelength change of the light by gravity, corresponding with theoretical calculations too.
The controversy can be resolved if we consider the resistance effect of the local forces against the stretch and squeeze of the space. We know very little about the resistance of local forces against the gravitational waves, but this effect must exist. As the universe expands, space itself expands everywhere. However, we do not see that the local structures, galaxies, solid materials expand. Anything held together by local forces resists the space expansion. The LIGO arms are solid materials held together by local forces, hence resist space expansion or contraction. The space itself with the light waves contracts and expands, yet the measuring arms do not or not the same way, causing the interference pattern change. This effect could explain the observed results in the LIGO experiment and also resolve the controversy.
Is this mean that the light is going faster or slower than the light-speed when space squeezes? To solve this still seemingly existing impossibility, we must differentiate between traveling in space and traveling on space. When we travel in space, there is a maximum speed, the light speed, which cannot be overpassed, and only bosons, massless particles, like the light particles, photons, can have. These massless particles cannot travel in space in the vacuum at a different speed than the light speed either.
However, traveling on space is a different scenario. When space itself moves, for example, expands, it grabs everything, with it what is in it. There is a scientific consensus that there are objects, which are far enough, they are receding faster than the light speed from us because of the accumulating effect of space expansion between us. This effect must be present on smaller scales also. The light is attached to space, so the space expansion or contraction by the gravitational waves must grab the photons with it. In this case, the light travels on space, not in space, so its speed can differ from the light speed traveling in space.
There is a possible physical experiment to prove that the above-described scenario is the right explanation and the correct description of the physical reality of the LIGO measurement. If we get rid of the solid tube of the arms of the gravitational-wave measuring device, the interference pattern change should be different. If the measuring device is space-based, there is still local bound present, the gravity, but gravity is a much less strong force than the electromagnetic interaction, which is responsible for the binding in the arms of the LIGO device, so the change of the interference pattern should be different compared to a similar Earth-based device. The planned space-based gravitational-wave detector might show proof of the described theoretical view if it saw a different change in the interference pattern than seen in the Earth-based devices.
However, the other question mentioned concerning the resolution of the LIGO experiment, which was discussed in the earlier thought remains open.
No comments