Einstein's Theory of Gravity Passes Toughest Test to Date: Equivalence principle in extreme conditions

[steve_bank]

What if gravity and QM don't inherently play nice and nothing can change that. Is that possible??

One way to look at it is as piecewise approximation. Common in technology. We do not know what reality is, we have no reference point. What we do is develop and test models that work over a specified set of conditions. Newtonian vs relativistic and quantum mechanics.

 

[steve_bank]

That is a relief, for a while I was worried gravity might stop working.

Jokes aside, this wasn't about testing whether or not gravity exists.

Right now, Relativity is the only explanation for gravity that we have. Everyone knew about the fact of gravity long before science was a thing. Newton introduced the law of gravity in the 1600s. It wasn't until Einstein cooked up Relativity that we had a theory of gravity to go with the law of gravity. Relativity doesn't play nice with quantum anything, so either there is a problem with relativity, a problem with quantum, or a third thing no one has discovered yet.

Starting with Maxwell and Einstein we have been awash with continuous scientific revolution. At one point AE had what we call today rock star cultural status. After long immersion it is hard to get overly excited.

 

[Underseer]

That is a relief, for a while I was worried gravity might stop working.

Jokes aside, this wasn't about testing whether or not gravity exists.

Right now, Relativity is the only explanation for gravity that we have. Everyone knew about the fact of gravity long before science was a thing. Newton introduced the law of gravity in the 1600s. It wasn't until Einstein cooked up Relativity that we had a theory of gravity to go with the law of gravity. Relativity doesn't play nice with quantum anything, so either there is a problem with relativity, a problem with quantum, or a third thing no one has discovered yet.

Starting with Maxwell and Einstein we have been awash with continuous scientific revolution. At one point AE had what we call today rock star cultural status. After long immersion it is hard to get overly excited.

Einstein doesn't impress you?

How many other theories of gravity are out there?

 

[steve_bank]

Starting with Maxwell and Einstein we have been awash with continuous scientific revolution. At one point AE had what we call today rock star cultural status. After long immersion it is hard to get overly excited.

Einstein doesn't impress you?

How many other theories of gravity are out there?

If by impressed you mean hearing angelic choirs at the sound of his name, no. From his authorized bio I read, he was onseccessd more so than his peers. There was a stretch at Princeton where he was said to not undress at night, too distracting.

He did not create in a vacuum, he built on what came before. As did Maxwell. AE made a great leap but he probably sacrificed a lot. Total immersion and dedication. At that he was in some ways a one hit wonder.Sciemce like anything is a learned skill. Back in the 80s I worked witrh a physicist who prieviously worked at MIT Lincoln Labs. As he put it, it was a workaday environment. People came in, worked, and went home. I was emersed in th environmnt for so long the creative aspects became routine. As my physicist friend put it, part of it is learning and effort, and a big part of it is serendipty. Things have to line up for you.

 

[lpetrich]

Returning to tests of general relativity, I have mentioned the equivalence principle.

There are several other tests of GR, and it has passed them so far.

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Post-Newtonian tests: weak field, quasi-static. Post-Newtonian means the next order of series expansion after the Newtonian limit. It covers Solar-System tests and most other tests involving orbiting celestial bodies. Post-Newtonian effects are about (v/c)^2 times Newtonian ones, where v is a typical velocity. Furthermore, (v/c)^2 is around G*M/r for size scale r and dominant mass M.

The main parameters:

(gamma) = (space distortion) / (time distortion)
(beta) = (nonlinearity in time distortion)
To lowest order, time distortion makes Newtonian gravity.

Both parameters are very close to their GR values, (gamma) about 2*10^(-5) from 1 and (beta) about 3*10^(-3) from 1.

SEP violations are also post-Newtonian in size.

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Turning to gravitational waves, we have several tests.

The first observed evidence of them was the inspiral of some binary pulsars. The observed rates agree closely with predictions made with GR.

Some G-wave bursts were recently detected, and they have the shapes that one would expect from inspiraling neutron stars and black holes, as calculated with GR.

The neutron-star G-wave burst arrived about a second before a gamma-ray burst, having traveled some 140 million light-years from galaxy NGC 4993. Thus indicating that their propagation speeds are very close.

 

[Jobar]

What if gravity and QM don't inherently play nice and nothing can change that. Is that possible??

We see that the universe exists, so obviously the phenomena which we try to describe with QM and relativity 'play nice' together. But as others have said, our models, descriptions, mathematical formulations of that play don't jibe with each other.

If the universe is impossible for us to model with arbitrary accuracy- and Heisenberg proved that it is- then it may be that the mystics are right, and even our approximate models are illusory. But I simply don't know if that's so or not- no one does, really.

 

[lpetrich]

There was something similar in physics in the late nineteenth century.

Newtonian mechanics had been an enormous success, successfully predicting the motions of Solar-System bodies, and also the motions of binary stars. This success extended to calculation of perturbations of orbits: orbits of planets by other planets, and orbits of moons by the Sun, planet equatorial bulges, and other moons.

Electromagnetism was also a success. It unified what was known about electric and magnetic fields and their interactions. Visible light turned out to be an electromagnetic wave, and late in that century, a certain Heinrich Hertz succeeded in making electromagnetic waves using macroscopic electric currents.

However, there was a BIG problem. A BIG BIG problem.

Maxwell's equations predict that electromagnetic waves in a vacuum will have a constant speed: c. But according to Newtonian mechanics, it ought to be possible to catch up to *any* moving object if one tries hard enough. Thus, nothing will have an always-constant speed. Meaning that the two sets of theories did not play well with each other, despite their enormous success otherwise.

A variety of solutions were proposed for this conundrum. One of them was the ether theory, that Maxwell's equations are strictly true only when one is stationary relative to the ether. Otherwise, the equations have extra terms from one's velocity relative to the ether. Another one was the source theory. It is something like the ether theory, but with Maxwell's equations referred to electromagnetic-field sources.

In 1887, Albert Michelson and Edward Morley tried to test the ether theory by sending light in two different directions and comparing the speed in each direction. They did see some nonzero effect, but it was about the size of the accuracy of the experimental apparatus, and it was distinctly less than what one would expect from the Earth's orbital velocity around the Sun.

That was big trouble for the ether theory.

Does matter drag the ether? That would explain this experiment, but it had trouble with the Fizeau experiment about the speed of light in moving liquids. That experiment's results indicated no dragging.

Physicists struggled to find solutions, until Albert Einstein succeeded with special relativity in 1905. It did not need that ether, and it got around the incompatibility by modifying Newtonian mechanics to make c a cosmic limiting speed.

 

[skepticalbip]

Starting with Maxwell and Einstein we have been awash with continuous scientific revolution. At one point AE had what we call today rock star cultural status. After long immersion it is hard to get overly excited.

Einstein doesn't impress you?

How many other theories of gravity are out there?

If by impressed you mean hearing angelic choirs at the sound of his name, no. From his authorized bio I read, he was onseccessd more so than his peers. There was a stretch at Princeton where he was said to not undress at night, too distracting.

He did not create in a vacuum, he built on what came before. As did Maxwell. AE made a great leap but he probably sacrificed a lot. Total immersion and dedication. At that he was in some ways a one hit wonder.Sciemce like anything is a learned skill. Back in the 80s I worked witrh a physicist who prieviously worked at MIT Lincoln Labs. As he put it, it was a workaday environment. People came in, worked, and went home. I was emersed in th environmnt for so long the creative aspects became routine. As my physicist friend put it, part of it is learning and effort, and a big part of it is serendipty. Things have to line up for you.

You gotta give him credit for at least three hits, and each in a very different branch of physics.

1.. In the late 1800s there was a lot of argument as to whether atoms actually exist. Those on the pro side also had arguments as to the size. Albert not only verified that atoms exist but determined their size.

2.. He discovered and modeled the photoelectric effect. For this he was awarded the Nobel prize.

3.. Then, of course, there is his theory of relativity.

.. He also did a lot of work with the big boys of QM. I don't know how much of a contribution he made but he was certainly consulted by the known actors in that field.

 

[steve_bank]

If by impressed you mean hearing angelic choirs at the sound of his name, no. From his authorized bio I read, he was onseccessd more so than his peers. There was a stretch at Princeton where he was said to not undress at night, too distracting.

He did not create in a vacuum, he built on what came before. As did Maxwell. AE made a great leap but he probably sacrificed a lot. Total immersion and dedication. At that he was in some ways a one hit wonder.Sciemce like anything is a learned skill. Back in the 80s I worked witrh a physicist who prieviously worked at MIT Lincoln Labs. As he put it, it was a workaday environment. People came in, worked, and went home. I was emersed in th environmnt for so long the creative aspects became routine. As my physicist friend put it, part of it is learning and effort, and a big part of it is serendipty. Things have to line up for you.

You gotta give him credit for at least three hits, and each in a very different branch of physics.

1.. In the late 1800s there was a lot of argument as to whether atoms actually exist. Those on the pro side also had arguments as to the size. Albert not only verified that atoms exist but determined their size.

2.. He discovered and modeled the photoelectric effect. For this he was awarded the Nobel prize.

3.. Then, of course, there is his theory of relativity.

.. He also did a lot of work with the big boys of QM. I don't know how much of a contribution he made but he was certainly consulted by the known actors in that field.

In terms of impact tje photoelectric effect was more important than relativity. His papers on relativity were a a hard sell especially from an unknown. I believe he rejected QM to some degree.

Of course he was at the top and had an extrordinaty journey. Physics back then was an informal association of peers. There were few distractions unlike tosay, he was working 24/7.

From his bio he was very much a human. He liked to eat, drink, smokle and talk physics with peers. In his day he liked to party.

I saw a picture of him standing in front of an observatory he helped design. Phalic and controversial in the day. The best way I can descibe his dress is stylish. Far from the stoic button down science image.

I just do not put him at the top in terms of scope and importance overall. AE did give credit to Maxwell, he said he stood on the shoulders of giants.

Perhaps his greatest gift was reducing complex to simple images. In his bio he credits an uncle for that. He brought science into everybody's home.