NASA researchers intend to use lasers aimed at the moon to test a basic assumption of modern physics.
Dr. Tony Phillips, Patrick L. Barry, NASA
Four hundred years ago, according to the story, Galileo Galilei dropped objects from the Tower of Pisa: cannon balls, rifle balls, objects of gold, silver and wood. He may have expected the heavy objects to fall faster, but that was not the case. They all hit the ground at the same time, so he made an important discovery. Gravity accelerates all objects at the same rate, regardless of their mass or composition.
Today this fact is called "the universality of free fall" or the "principle of equivalence". It is one of the foundations of modern physics. In fact, Einstein created his theory of gravity, i.e. the theory of general relativity, assuming that the principle of equivalence is true.
But what if he is wrong?
"There are modern theories that actually claim that the acceleration of free fall does depend to some extent on the material composition of the object," says Jim Williams, a physicist at NASA's Jet Propulsion Laboratory (JPL). If this is the case, it will be necessary to rewrite the theory of relativity, there will be a revolution in physics.
A group of NASA-funded researchers intend to test the equivalence principle by aiming laser beams at the moon.
"Distance measurement with lasers is one of the most important tools we have for looking for flaws in Einstein's theory of general relativity," says Slava Torishev, a research scientist at JPL (Jet Propulsion Laboratory) who works with Jim Williams and others on the project.
The experiment is possible, because more than 30 years ago the astronauts from Apollo left mirrors on the moon - a small array of reflecting mirrors, which, when hit by a laser beam from Earth, reflect it straight back. With the help of the lasers and mirrors, researchers are able to precisely follow the movement of the moon around the earth.
This is a modern version of the Leaning Tower of Pisa experiment. Instead of dropping balls to the ground, the researchers will observe the fall of the Earth and the Moon towards the Sun. Similar to rifle balls and cannonballs, the Earth and the Moon are also made of a different composition of elements, and have different masses. Are they accelerating towards the sun at the same rate? If so, the principle of equivalence is valid. If not, prepare for a revolution.
Violation of the principle of equivalence will be revealed experimentally as the curvature of the moon's orbit, in the direction of the sun or away from it. "It is possible that by using large masses like the Earth and the Moon we can see this tiny effect, if it exists," Williams notes.
Scientists have been tracking the moon's orbit since the days of Apollo. So far, Einstein's general theory of relativity - and the principle of equivalence - have met the experimental test to an accuracy of about one-tenths to the 13th power. However, this accuracy is not high enough to test the theories competing to inherit the place of relativity.
Current measurements of the distance to the moon using lasers - a distance of about 385,000 kilometers - reach an accuracy of about 1.7 centimeters. The new facility funded by NASA and the National Science Foundation, which will start operating in the fall, will increase the accuracy tenfold to an error range of about a millimeter or two. The exact step up will allow scientists to discover ten times smaller deviations from Einstein's general theory of relativity. This level of accuracy may be sensitive enough to detect the first evidence of defects.
In order to achieve this accuracy, the facility, called APOLLO (Apache Point Observatory Lunar Laser-ranging Operation), must measure the time it takes for the laser pulses to travel from the moon and back with an accuracy of a few picoseconds, only a trillionth of a second (a second divided by ten to the 12th power). The speed of light is known, about 300,000 kilometers per second, so the time measurement tells scientists the distance between the APOLLO telescope and the mirror on the surface of the moon.
How did the APOLLO reach a tenfold improvement? For starters, he uses a larger telescope than the previous facility at the McDonald Observatory in Texas - 3.5 meters compared to 0.7 meters. APOLLO's larger mirror allows it to capture more photons of light returning from the moon, explains Tom Murphy, a professor at the University of California, San Diego and the designer of the APOLLO facility. The smaller telescope captures an average of one photon for every 100 outgoing laser pulses (each pulse includes more than ten to the 17th power!). The APOLLO telescope will capture about five photons from each pulse, which will significantly improve the statistical strength of the results.
The planners had to deal with several possible disturbances. The Earth's atmosphere, for example, may tilt the path of the light beam similar to how it causes the stars to twinkle. Also, tiny tectonic movements of the ground under the APOLLO observatory, measured by a few centimeters per year, may bias the results in the long run. That's why the project managers chose a mountain peak near White Sands, New Mexico. The atmosphere in the area is extremely calm, and so is the ground under the observatory. In addition, a superconducting gravimeter and a GPS sensor were installed near the observatory to detect subtle movements of the ground, and barometers will map the state of the atmosphere.
Williams and Turishev recently received a grant from NASA's Office of Biological and Physical Research to scale up JPL's laser ranging analysis software to match the new capabilities of the facility in New Mexico. "It will be necessary to deal with all kinds of small effects at the millimeter level," Torishev points out.
Meticulous measurements of such tiny effects may cause the fall of the universality of free fall…
Many physicists will welcome the news. They have been bothered for years by the intriguing inconsistency between general relativity and quantum mechanics. The two theories, each of which is very successful in its field, are compared to two different languages that describe the universe in two fundamentally different ways. Finding flaws in the theory of general relativity may lead to a new theory of everything, which will combine quantum physics and gravity into one harmonious theoretical framework.
From Pisa, Italy, to the moon, to White Sands, New Mexico: this is a vast experiment, spanning hundreds of years and hundreds of thousands of miles. Soon we may have the answer.
Translation: Dikla Oren
3 תגובות
Even if it turns out that the earth and moon fall at a different rate towards the sun, the reason will lie in the process of their formation and the amount of energy used during their formation.
Alon, do you even understand anything about physics? Because if not, then your comment is pointless.
Over the years, hundreds of different theories have arisen, which contradict each other. As you believe in the theory of relativity, so people believed in those different teachings.
If you studied physics at university (and I'm assuming you don't), you would be exposed to a number of theories, each of which seems very logical, but different from each other.
A theory, by virtue of being a theory, is merely a very well-founded hypothesis. Over the years, many theories came out, each of which was the "truth" of humans, until a new theory came out that contradicted it.
Even as a physicist, you cannot know whether a theory is true or not, but only assume that it is true. In any case, you must not rule out a theory. In physics, everything is very precise, so even a millionth of a second may turn out to be a new discovery. Before relativity came out, do you think anyone imagined that matter could turn into energy? After all, Newton is considered the father of physics, and one of the issues he discussed and championed is the law of conservation of matter, and Einstein's theory contradicts this law. So here you have a perfect example of theories being theories, and they are only true until someone proves otherwise.
These scientists you are laughing at are people of high rank and above, with doctorates and professorships. They understand physics more than anyone else, especially more than me, you, or the author of the article. So if they say something, it has a basis that you may not be exposed to, but it is alive and well.
There are a lot of unsolved questions today, and at least I can't even imagine their solution, but one day someone will come up with a theory that will solve the problem and then it will be obvious to everyone that this is the solution, but today we still can't find it. In conclusion, they may be right, and they may not. It is impossible to determine. In both cases, you have no right to judge anyone. An error of one millionth of a second is a critical error, because if a theory is correct, the calculations must come out perfect, and not almost or approximately.
It's a little ridiculous and a little sad how they cling to an accuracy error of one millionth of a second to refute such a well-founded claim as Einstein's and Galileo's Torah..