Questions about LIGO

A recent scientific breakthrough was created by the LIGO, the Laser Interferometer Gravitational Wave Observatory project. The project op...

A recent scientific breakthrough was created by the LIGO, the Laser Interferometer Gravitational Wave Observatory project. The project opened a new window in the universe. It is provided a new way of observation by observing the universe through gravitational waves. It was a real breakthrough. Not just because it creates a new image of the universe, but it has used the technology of a never seen level of sensibility. The gravity is so weak that the equipment must have the measuring sensibility of much less than the diameter of a nucleon. It is the sensibility similar to measure the closest star's distance by less than the thickness of a hair.

The LIGO is practically a measuring tape, which measures distances. It uses the interference method to compare distances to provide the necessary sensibility. In the equipment, two coherent laser beams are traveling in two, four-kilometer long perpendicular channels. When the two laser beams reflected back by mirrors to the starting point where the beams were created from a single laser beam by a splitter, the two beams are united again, and they create interference with each other as they meet. The created interference is very sensitive to the distance what the two beams travel in the channels. If either one is traveling just a little different distance, the interference will change, and the united light will differ. With these settings, the equipment has the sensibility of much less than the wavelength of the used laser light. To enhance the sensibility of the distance change to the required level, the laser beams are reflected back and forth 280 times in the channels before they become united again. This way, the size change of the channel is overstated by 280 times, so the equipment has the sensibility even less length change than the actual length change of the channels. By this technique, the length of the channels enhanced to more than 1100 kilometers.

Why is this length or distance measurements? Because the gravitational waves, as they travel through space, distort space-time, and change distances and lengths as they sweep across the universe. When a gravitational wave reaches the LIGO equipment, it changes the length of the channels. Because the nature of the gravitational waves, this change can be observed by the most with measuring and comparing perpendicular distances.

Every accelerating mass creates gravitational waves, and not just that, but causes mechanical vibrations as well. Practically everything that is moving, especially in the vicinity of the measuring equipment, has an effect on the measurement, provide "noise" to the sensors. To filter out the local noises, the experiment uses two LIGO equipment, far from each other. If only one piece of equipment provides detection, most likely, it is caused only by some kind of disturbance in the vicinity, it is local noise, not a gravitational wave from a distance. The valuable measurements are only which are recorded by both pieces of equipment showing the same pattern of distortion.

Even this is not enough for an interesting measurement. The length distortion of the channels must have a specific pattern according to the theoretical calculation of a cosmic collision, which may create the gravitational waves, and which is recorded by the LIGO. Only if an expected pattern of length distortion appears at both LIGO sites is considered as a gravitational wave traveling in the universe.

With these settings, the LIGO is considered to be able to sense, to measure and to record gravitational waves emitted by colliding black holes or neutron stars, more than a billion light-years away.

The LIGO already provided positive measurements. According to the interpretation of the recordings, there were colliding black holes and neutron stars. By examining the measurements of the two LIGO equipment, scientists were able to provide directions and distances in the sky, where these cataclysmic events occurred. More conventional telescopes backed up the observations of the LIGO and identified real cosmic objects.

The LIGO project is an essential and powerful tool to acquire more knowledge about the universe. However, the utilized methods of the measurement raise questions. What are these?

The interference method

LIGO's measurement method is built on the interference of coherent light waves. However, when gravitational waves distort space-time, they distort everything that is in the space. It is an already measured effect that the gravity distorts light waves as well. As the lengths of the channels distorted by the gravitational waves, everything will be distorted what is in the channels. The light waves become distorted too. Therefore, when the gravity distorts a light wave, it means the light wave changes its frequency, or what is the same, changes its wavelength.

The two light beams would not shift phase at the point where they united in the LIGO equipment. The actual length of the channels do not change in the unit of the wavelength of the measuring light because not just the length of the channels change by the gravitational distortion, but the wavelength of the light change in proportion too. Like a wavy line is drawn on a rubber band. If the rubber band is stretched, will not be more waves on the rubber band, only the wave of the line will be distorted.

If the length of the channel were a given wavelength long, it would not change as its length changes. The length of the wavelength will change according to the length distortion of the channel. So, the phase of the wave at the end of the channel, where the recombination of the two light beams occurs, does not change by the change of the length of the channels. The two light beams will be in the same phase, in the same coherence as they were before, only their wavelength or frequency will be different, and as that means, their energy will differ. Would this energy difference could provide the same change of interference as they would create if they stay on the same wavelength? The main difference is that the waves shift phase at the point of the recombination if their wavelengths remain the same, and they remain in the same phase with different energy if they change their wavelengths. Moreover, this energy difference is exceptionally tiny, must be much less than the interference method can provide in the case of the phase shift.

Are the two, fundamentally different cases still could provide the same effect on the measurement? If not, then this method of measurement could not provide the expected result.

The distance enhancement method

Gravitational waves travel with the speed of light, according to our current physics. How can the length enhancement method - used in the LIGO project - create more sensitivity in the measurement? Would not measure the reflected light beam a different phase of the gravitational wave than the forwarding beam? Would not measure the many times reflected light beam an entirely different phase of the gravitational wave, which is an entirely different actual distortion of the space-time? Can the method of reflecting the light beams - to enhance the change of the length of the channels for enhancing the sensitivity - works if the gravitational waves travel with the same speed as the measuring light waves travel? Would not the light, which travels back and the light, which travels forth measure a different phase of the gravitational waves - sometimes by expanding the space and sometimes by contracting the space - in the same measurement? We can experience the condition of the traffic on the road only if we travel at the same speed as the traffic. If we are going slower or even backward, we will experience different conditions of the traffic.

The sensibility enhancement by the reflected light waves may not work, this method may not enhance the sensibility of the measurement. This method of length enhancement to create more sensibility works only with a proportionally longer gravitational wavelength. The actual distance that a light-quanta travels in the channel is more than 1100 kilometers. The equipment cannot measure gravitational waves with less wavelength. Even half of the gravitational wavelength should be the lower limit - at least - the length of the measured distance, but longer is the gravitational wavelength, better the accuracy using this method. However, the diameters of the stellar black holes or neutron stars are usually well below 100 kilometers. Before their collisions, when the gravitational waves are the most intense, the colliding objects are in less distance than a thousand kilometer, so their rotation around each other creates less than a thousand-kilometer wavelength gravitational waves. The LIGO cannot measure shorter gravitational wavelengths precisely. For less than at least a thousand kilometer wavelengths - practically, even at greater lengths - the measurement would create random measured values of the distortions.

The LIGO measures gravitational waves just before the collisions, as the recorded patterns show. The gravitational wavelengths, that the LIGO can measure are longer than the created wavelengths of the colliding objects. If this statement is true, yet the measurement is positive, do the observations consider the necessary wavelength expansion? Moreover, what would cause this expansion? If the gravitational wavelength expansion is considered in the calculations, is it considered as an effect caused by the expansion of the universe? No other cause is possible, and the expansion of the universe indeed has an expanding effect on the gravitational waves. If the expansion of the universe is considered and calculated in the measurements, then the LIGO can be sensitive only for those colliding stellar objects, which are at least in a specific distance, because LIGO's sensitivity requires a minimum length of gravitational wavelength.

Moreover, if the expansion of the universe causes the gravitational wavelength expansion, then the recorded gravitational wave-frequency is proportionally less than the theoretically calculated, also. Is the measured frequency shows that effect? If yes, then the LIGO would be a capable tool to measure the expansion rate of the universe also, by correlating the theoretical and the actual wave frequency of the colliding objects.

However, the effects described above and their consequences are not mentioned in the publications of the LIGO.

These are the questions concerning the measurement of the LIGO project. If enhancing the sensibility reflecting by many times the light beams cannot work, and the shift of the frequency of the measuring light does not provide the same coherence effect as coherent light waves would do, are the results of the measurements still can be considered accurate? Is the LIGO equipment the right tool to find and measure the gravitational waves?

Moreover, are there other methods to measure gravitational waves, to measure the distortion of the space-time? Another possible method of consideration will be in a subsequent thought.