What is the smallest mass proven to have gravity?

[Klaynos]

What is up?

 

The vector direction opposite to the vector towards the local gravitational centre of mass.

 

You can extrapolate this to down.

 

I don't really understand the difficulty here.

[Robittybob1]

What is up?

 

The vector direction opposite to the vector towards the local gravitational centre of mass.

 

You can extrapolate this to down.

 

I don't really understand the difficulty here.

I was trying to understand where upwards finished. For downwards terminates in the "local gravitational centre of mass", but where does upwards finish? Is it just being forever repelled rather than "falling upward" toward anything?

 

Upwards begins where downwards ends. Downwards begins where upwards ends so they are symmetric.

Edited March 24, 2016 by Robittybob1

[John Cuthber]

 

 

No, not really.

 

Imagine a neutrino time-of-flight measurement (similar to the one a few years ago, but without the bias that gave the superluminal result). You determine that the speed of a neutrino is c ± 0.001 m/s. That doesn't mean there's a 50% chance that it travels faster than c — that would violate some well-established physics. To make that claim, you would need a result above c where c was statistically excluded.

Actually, that would mean that the speed should be reported as C-0.001m/s ± 0.0005 m/s

[Robittybob1]

Actually, that would mean that the speed should be reported as C-0.001m/s ± 0.0005 m/s

The thread is about "What is the smallest mass proven to have gravity?" Try to bring it back to the topic please.

 

Under the action of just gravity on earth the antimatter particle would go upwards - ie repulsion rather than attraction. NB This is very very unlikely - it is just that we do not have the tech to rule it out yet

Why did you think it was unlikely? Isn't that just antimatter curving spacetime in the opposite direction?

[swansont]

Do we then put a set of coordinates on an antimatter particle and one on a matter particle and see in which direction they move under the influence of their own gravity? If they move away from each other they fall upwards. That would work in deep space but all experiments are done under Earth's gravity which is going to define "down". So is "up" just the opposite to our down?

 

 

No, their gravitational influence on each other is way too small. That answer has not changed since it was discussed less than two weeks ago in this very thread.

[Robittybob1]

 

 

No, their gravitational influence on each other is way too small. That answer has not changed since it was discussed less than two weeks ago in this very thread.

ALPHA is doing an experiment. http://www.nature.com/ncomms/journal/v4/n4/fig_tab/ncomms2787_F2.html The graph of the average location of annihilation seems to be dropping with time. Wouldn't that suggest they do fall on average? Yet they don't come to that conclusion. Do you understand what that falling average line means?

I'm thinking the annihilation must occur where the matter and antimatter is so if on average that location is lower wouldn't that imply they are falling down rather than falling up?

[Strange]

So is "up" just the opposite to our down?

 

That sounds about right: the radial direction away from the centre of mass instead of towards it.

 

 

http://www.nutriculamagazine.com/a-new-approach-of-gravity-effect-on-antimatter-cern/ article describing an actual experiment.

 

That is the ALPHA experiment linked to earlier. They are constantly improving this by creating larger amounts of anti-hydrogen to test.

I was trying to understand where upwards finished.

 

Why would it finish?

Why did you think it was unlikely? Isn't that just antimatter curving spacetime in the opposite direction?

 

It introduces problems with conservation of energy (working out the details are left as an exercise for the reader - but you will get a clue from Jules Verne's The First Men in the Moon).

[swansont]

ALPHA is doing an experiment. http://www.nature.com/ncomms/journal/v4/n4/fig_tab/ncomms2787_F2.html The graph of the average location of annihilation seems to be dropping with time. Wouldn't that suggest they do fall on average? Yet they don't come to that conclusion. Do you understand what that falling average line means? I'm thinking the annihilation must occur where the matter and antimatter is so if on average that location is lower wouldn't that imply they are falling down rather than falling up?

This has nothing to do with what I posted.

[Robittybob1]

This has nothing to do with what I posted.

It wasn't clear from your post what in actual fact you were referring to.

 

No, their gravitational influence on each other is way too small. That answer has not changed since it was discussed less than two weeks ago in this very thread.

With these hydrogen antihydrogen interactions they are looking how they move in the Earth's gravitational field aren't they? Not looking at the amount of gravity between them.

 

....

It introduces problems with conservation of energy (working out the details are left as an exercise for the reader - but you will get a clue from Jules Verne's The First Men in the Moon).

Conservation of energy - I'll keep that in mind as I study EFE.

 

Just from this abstract it looks like it would an interesting read.

 

 

CPT symmetry and antimatter gravity in general relativity

http://iopscience.iop.org/article/10.1209/0295-5075/94/20001/fulltext/

 

Abstract. The gravitational behavior of antimatter is still unknown. While we may be confident that antimatter is self-attractive, the interaction between matter and antimatter might be either attractive or repulsive. We investigate this issue on theoretical grounds. Starting from the CPT invariance of physical laws, we transform matter into antimatter in the equations of both electrodynamics and gravitation. In the former case, the result is the well-known change of sign of the electric charge. In the latter, we find that the gravitational interaction between matter and antimatter is a mutual repulsion, i.e. antigravity appears as a prediction of general relativity when CPT is applied. This result supports cosmological models attempting to explain the Universe accelerated expansion in terms of a matter-antimatter repulsive interaction.

CPT symmetry? Wikipedia link https://en.wikipedia.org/wiki/CPT_symmetry

 

Charge, Parity, and Time Reversal Symmetry is a fundamental symmetry of physical laws under the simultaneous transformations of charge conjugation ©, parity transformation (P), and time reversal (T). CPT is the only combination of C, P and T that's observed to be an exact symmetry of nature at the fundamental level.[1] The CPT theorem says that CPT symmetry holds for all physical phenomena, or more precisely, that any Lorentz invariant local quantum field theory with a Hermitian Hamiltonian must have CPT symmetry.

.

Edited March 25, 2016 by Robittybob1

[swansont]

It wasn't clear from your post what in actual fact you were referring to.

With these hydrogen antihydrogen interactions they are looking how they move in the Earth's gravitational field aren't they? Not looking at the amount of gravity between them.

 

 

Correct. The gravity of the earth. As opposed to how they "move under the influence of their own gravity".

[Robittybob1]

 

 

Correct. The gravity of the earth. As opposed to how they "move under the influence of their own gravity".

If you just had coordinates and no gravitational mass then you would be just left with how they "move under the influence of their own gravity".

Post #50. If there were just coordinates I wasn't sure how or why you would call any of them up or down.

I suppose you could say "above or below the x axis" but this is a bit different than talking about gravity on the surface of a larger body. e.g. the hammer and the feather fall (down) the same rate on the Moon.

 

If there were 2 particles in deep space attracted or repulsed by self gravity I wouldn't call that movement up or down.

 

Up and down are indications of direction. They don't terminate, as such. The coordinate system doesn't care that the earth is there; the axes extend to infinity. That the earth gets in the way of the motion is a constraint of the specific problem.

 

Do we then put a set of coordinates on an antimatter particle and one on a matter particle and see in which direction they move under the influence of their own gravity?

Edited March 25, 2016 by Robittybob1