Einstein’s theory of general relativity passes another test
Researchers used a satellite orbiting the Earth to carry out an ultra-precise test of a core premise of Einstein’s theory of general relativity, which is the modern theory of gravity.
The question is whether two different kinds of mass — gravitational and inertial — are identical.
The scientists found that two objects aboard the satellite fell toward Earth at the same rate, with an accuracy of one part in a quadrillion.
This successful test of Einstein’s theory has substantial implications for current cosmic mysteries — for example, the question of whether dark matter and dark energy exist.
Fooling the ancients
Gravity is the force that holds the Universe together, tugging at distant galaxies and guiding them in an eternal cosmic dance. The strength of gravity is governed partly by the distance between two objects, but also by the masses of objects. An object with more mass experiences more gravity. The technical name for this type of mass is “gravitational mass.”
Mass has another property, which one might call inertia. This is an object’s tendency to resist changes in motion. In other words, more massive things are harder to move: It’s easier to push a bicycle than a car. The technical name for this type of mass is “inertial mass.”
There is no reason a priori to assume that gravitational mass and inertial mass are the same. One governs the force of gravity, while the other governs motion. If they were different, heavy and light objects would fall at different rates, and indeed philosophers in ancient Greece observed that a hammer and a feather fall differently. Heavy objects certainly do seem to fall faster than light ones. We now know that air resistance is the culprit, but that was hardly obvious in the past.
The situation was clarified in the 17th century, when Galileo performed a series of experiments using ramps and spheres of different masses to show that objects of different masses fall at the same rate. (His oft-cited experiment of dropping balls from the Tower of Pisa is probably apocryphal.)
And in 1971, astronaut David Scott convincingly repeated Galileo’s experiment on the airless Moon, when he dropped a hammer and a feather, and they fell identically. The ancient Greeks had been fooled.
Dark conjecture
The assertion that inertial and gravitational mass are the same is known as the equivalence principle, and Einstein hard-wired equivalence into his theory of gravity. General relativity successfully predicts how objects fall in most circumstances, and the scientific community accepts it as the best theory of gravity.
However, “most” circumstances does not mean “all,” and astronomical observations have revealed some perplexing mysteries. For one, galaxies rotate faster than their stars and the gases within them can account for or than Einstein’s theory of gravity can explain.
The most accepted explanation for this discrepancy is the existence of a substance called dark matter — matter that does not emit light. Another cosmic conundrum is the observation that the expansion of the Universe is accelerating. To explain this oddity, scientists have postulated that the Universe is full of a repulsive form of gravity called dark energy.
However, these are matters of informed conjecture. It could be that we do not fully understand gravity or the laws of motion. Before we can have any confidence that dark matter and dark energy are real, we need to validate Einstein’s theory of general relativity with very high precision. To do that, we need to show that the equivalence principle is true.
While Isaac Newton tested the equivalence principle back in the 1600s, modern efforts are much more accurate. In the 20th century, astronomers bounced lasers off mirrors left on the moon by Apollo astronauts to show that inertial and gravitational mass are the same to an accuracy of one part in 10 trillion. That achievement was impressive. But the most recent experiment went further still.
General relativity passes another test
A group of researchers called the MicroSCOPE collaboration launched a satellite into space in 2016. Cylinders of titanium and platinum were on board, and the scientists’ intent was to test the equivalence principle. By putting their apparatus in space, they isolated the equipment from vibrations and small gravitational differences created by nearby mountains, underground oil and mineral deposits, and the like.
The scientists monitored the location of the cylinders using electric fields. The idea is that if the two objects orbited differently, they would need to use two different electric fields to keep them in place.
What they found was that the required electric fields were the same, allowing them to determine that any differences in inertial and gravitational mass came out to less than one part in a quadrillion. Essentially, they made a precise validation of the equivalence principle.
While this is an expected outcome from the point of view of general relativity, it has very substantial consequences for the study of dark matter and dark energy. While those ideas are popular, some scientists believe that the rotational properties of galaxies can be better explained by new theories of gravity. Many of these alternative theories imply that the equivalence principle is not quite perfect.
The MicroSCOPE measurement saw no violation of the equivalence principle. Its results rule out some alternative theories of gravity, but not all of them. Researchers are preparing a second experiment, called MicroSCOPE2, that should be about 100 times more precise than its predecessor.
If it sees deviations of the principle of equivalence, it will give scientists crucial guidance toward developing new and improved theories of gravity.
See more here bigthink.com
Please Donate Below To Support Our Ongoing Work To Defend The Scientific Method
PRINCIPIA SCIENTIFIC INTERNATIONAL, legally registered in the UK as a company 
incorporated for charitable purposes. Head Office: 27 Old Gloucester Street, London WC1N 3AX.
Trackback from your site.
Herb Rose
| #
If inertial mass and gravitational mass are identical then the resistance to movement and the impetus to movement are equal and gravity cannot cause another object to move.
This is another experiment trying to confirm an existing belief. The red and blue shift show that Einstein’s theory are wrong. If the shift is due to the motion of the emitting object then the basis of relativity is wrong. If the shift occurs in the transmission of the light then time must exist at the speed of light and relativity is wrong.
The experts claim that the time dilation of the clocks on satellites proves Einstein is right. The data shows the clocks going faster closer to Earth and then slowing at higher altitudes. Einstein’s general relativity says that with greater velocity and and stronger gravitational fields time slows, so it predicts that the clocks on the satellites will go faster with increasing altitude. Anyone who thinks that the parabolic curve of the clocks proves the theory has an extremely low standard for what constitutes proof.
Reply
Ken Hughes
| #
Mass is mass, ‘simple as that. Mass is the measure of the energy contained within a lump of matter. There are no such physical entities as gravitational or inertial mass, only mass. Two different masses will accelerate the same in a gravitational field, (but differently if accelerated by one physical force), and that is presented as the “equivalence principle”.
The reason gravitational acceleration is independent of the mass of a falling body, is because the acceleration stems from a property of space time and not from any property the falling body has. The fundamental cause for gravitational acceleration is the changing of the rate of time, the slowing down of time, in the direction of the center of the mass causing the field. This is accepted science in that “Newtonian gravitation can be “expressed” in terms of time dilation”, (re. “Gravity from the Ground Up”, by Bernard Schulz).
However, the mainstream stops short of deducing a direct causality between time rate and gravitational acceleration because of the “curvature” of space in strong fields. There assertions are limited to weak fields only, to Newtonian gravity and not general relativity.
But this is a mistake. The “curvature” of space in strong fields, or the changing of the “size” of space in strong fields, is in fact, also caused by the same time curvature we get in the weak field. We can ignore it in weak fields because the effect is so small, but in strong fields the gravitational time dilation’s effect on space becomes significant and we need to use general relativity for our calculations. That’s the only difference between Newton and Einstein.
So, we can still claim that gravitational acceleration is the direct cause of acceleration in both weak and strong fields, and we can still say that gravitational acceleration is caused by the time curvature in the field, whether the field is strong or weak.
As for the galactic rotation anomaly, take a look at my video here ;-
https://www.bing.com/videos/search?q=answer+to+the+galactic+rotation+anomaly&view=detail&mid=C556430427118745CA79C556430427118745CA79&FORM=VIRE
There is no such thing as dark matter.
Reply
Herb Rose
| #
Gravitational mass is a downward vector caused by gravity. When a mass has motion in a direction other then down the vector changes as part of the mass becomes inertial and the downward or gravitational mass decreases.
This is seen in the design of race cars where aerodynamics is used to have the force of the wind providing increased downward pressure as the velocity increases, in order to maintain traction on the surface. Without this downward force from the wind at high speeds the gravitational vector will decrease to a point where the slightest bump will send the car airborne. This used to happen often in Bonneville Salt Flats attempts to set new speed records. If you wish to cross a bridge that will not hold your vehicle’s weight you need to go as fast as possible to convert as much mass as possible into forward momentum.
Herb
Reply
Lit
| #
“in the direction of the center of the mass causing the field”
But we can´t know if mass is causing the field or if the field is the cause of the mass.
Reply
Herb Rose
| #
Hi Lit,
In my opinion gravity is a result of energy and causes motion while inertia is a result of matter and resists motion. Because energy is attracted to positive matter and repels negative matter what we call mass is a measurement of how strongly the matter is held in an energy field.
Asteroids cannot orbit other asteroids according to Newton’s formula, and yet they do. This is a result of the energy field associated with the asteroid expanding, due to the weakening of the energy field being radiated by the sun, allowing for the energy fields of two asteroid to combine into one field similar to how the fields ofbthe Earth and moon combine to form one field orbiting the sun.
Herb
Reply
Lit
| #
“The strength of gravity is governed partly by the distance between two objects, but also by the masses of objects.”
Or, the distance between two objects and their masses are governed by gravity. I think mass is not the cause of gravity, its the effect of gravity. Like a charge.
Then the first law applies, ΔU=Q-W. Einstein tried to circumvent the first law, he tried to avoid the fact that all forces must have a source of energy that drives it, it needs power. Even if he says gravity is curvature in space, you need exactly the same amount of force/power to curve space.
Reply
Herb Rose
| #
The model illustrating general relativity is deceiving, giving a false sense of understanding. If you are going to represent the mass with a three dimensional image you cannot use a two dimensional plane to represent the four dimensions of space-time. Is the distortion of the plane a fifth dimension? A proper illustration would nave the mass as a two dimensional disk embedded in a three dimensional space-time solid. With this model the distortion would be in three dimensions around the disk and not provide an equatorial path for orbits. Have you ever seen a drawing where you go up four flights of stairs to arrive at the start point?
Reply
Kevin Doyle
| #
Dear Big think.com,
Your essay suggests Einstein was again validated, yet all you did was point out Galileo and Newton were correct. Einstein was more interested in being a celebrity, than solving real world problems.
The rest of your essay is typical masturbatory fantasy of dorks and geeks. None of you fantasy world has anything to do with reality on Earth.
Please, stop living with Peter Pan…
Reply