Time flows in One Direction

[mistermack]

...
And every particle in the universe is linked by gravity to every other.

For example, an atom in your finger, is linked to every particle in the Sun by gravity.
With a time delay of about 8 minutes. One hydrogen atom in the Sun won't have much effect on your finger, but it is linked. And each link has a minute effect...

What is the nature of this link called gravity?

I'd love to know, but I ain't no Einstein.
What rEv said is how Einstein put it. Although, to be accurate, it's a curvature rather than distortion. But other people say different things.
For instance :

"Spacetime" is simply a convenient mathematical construct - essentially plotting space and time on the axes of the same diagram - which makes it easier to explore the consequences of GR. It is not at all supernatural, nor mysterious, and it contains not a single quantum chakra!

How a convenient mathematical construct can become curved by the action of a bit of mass, a billion light years away, needs some explaining. But it's probably just a different way of viewing the same effect.

But Wikipedia says that gravity has an infinite range, and it cannot be absorbed, transformed, or shielded against.
So going by that, every particle that has mass has a gravitational link to every other.

I suppose it's a bit like a spider's web, where each part has a link to every other part. According to General Relativity, gravity isn't a force but an interaction. It certainly feels like a force and acts like a force though.

[pErvinalia]

The search is on for a hypothesized "graviton". A "particle" that transfers gravitational potential, or something like that .

[JimC]

Personally, I blame Higgs...

[mistermack]

The search is on for a hypothesized "graviton". A "particle" that transfers gravitational potential, or something like that .

That's what I find mysterious about gravity.
In some areas of physics they talk about gravity not being an actual force, but just being a consequence of the curvature of spacetime.
In other areas, it's a force, transmitted by the theoretical graviton particle. And the two ideas don't appear compatible.

[JimC]

The search is on for a hypothesized "graviton". A "particle" that transfers gravitational potential, or something like that .

That's what I find mysterious about gravity.
In some areas of physics they talk about gravity not being an actual force, but just being a consequence of the curvature of spacetime.
In other areas, it's a force, transmitted by the theoretical graviton particle. And the two ideas don't appear compatible.

I suspect that those 2 different ideas illustrate the gap between quantum physics and general relativity...

[pErvinalia]

Yep. Just two different abstractions of the same principle. Interestingly, there are some new experiments that are underway that anticipate being able to find "gravity waves" if they do exist. I think gravity waves, via the wave-particle duality, will be equivalent to there being a "graviton" particle.

[mistermack]

Yep. Just two different abstractions of the same principle. Interestingly, there are some new experiments that are underway that anticipate being able to find "gravity waves" if they do exist. I think gravity waves, via the wave-particle duality, will be equivalent to there being a "graviton" particle.

I thought that gravity waves had been verified? I have a vague memory of something in the last five years showing that they exist, or maybe just being consistent with them?
Something to do with the black hole in the centre of the Milky Way.
I could have that completely wrong though, I can't remember any details.

[mistermack]

The search is on for a hypothesized "graviton". A "particle" that transfers gravitational potential, or something like that .

That's what I find mysterious about gravity.
In some areas of physics they talk about gravity not being an actual force, but just being a consequence of the curvature of spacetime.
In other areas, it's a force, transmitted by the theoretical graviton particle. And the two ideas don't appear compatible.

I suspect that those 2 different ideas illustrate the gap between quantum physics and general relativity...

That's what bugs me about physics. Things are set in stone, for a while, and then it's all wiped away without any apology. Like Catholics eating meat on a Friday. All of a sudden, it's ok.

I've never been able to accept the basic tenet of relativity, that there is no "real" frame of reference.
While I'm happy to accept that there is no need for one, with what we know so far, it's always been a jump too far for me to believe it.
Now, I've noticed on the wiki page for the graviton, it says this :

Unlike the force carriers of the other forces, gravitation plays a special role in general relativity in defining the spacetime in which events take place. In some descriptions, matter modifies the 'shape' of spacetime itself, and gravity is a result of this shape, an idea which at first glance may appear hard to match with the idea of a force acting between particles.[9] Because the diffeomorphism invariance of the theory does not allow any particular space-time background to be singled out as the "true" space-time background, general relativity is said to be background independent. In contrast, the Standard Model is not background independent, with Minkowski space enjoying a special status as the fixed background space-time.[10] A theory of quantum gravity is needed in order to reconcile these differences.[11] Whether this theory should be background independent is an open question. The answer to this question will determine our understanding of what specific role gravitation plays in the fate of the universe.

So it's not just questionable whether gravity is caused by a particle, or curvature of spacetime, but it's also not settled whether space has a fixed background.
I wouldn't mind, but I've been on the wrong end of some heavy condescension, whenever I'VE suggested something similar.

[Brian Peacock]

'Gravity' and 'Gravitation' do not seem to be referring to the same 'thing'.

[mistermack]

'Gravity' and 'Gravitation' do not seem to be referring to the same 'thing'.

Yeh, it's a bit hard to work out what difference the author sees in the words.

My best guess is that he uses gravitation to refer to the whole process, including it's cause and effects, whereas he says gravity when he just means the force.

Except that it's not a force. Or is it?

[JimC]

'Gravity' and 'Gravitation' do not seem to be referring to the same 'thing'.

Yeh, it's a bit hard to work out what difference the author sees in the words.

My best guess is that he uses gravitation to refer to the whole process, including it's cause and effects, whereas he says gravity when he just means the force.

Except that it's not a force. Or is it?

If you truly believe that it is not a force, you can levitate...