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Physics, Astronomy & Cosmology / What is a small classical example of em radiation?

« on: 22/06/2020 14:24:01 »

 I am trying to find an example of an extremely small electric charge moving wrt to  a magnetized conductor and causing  a photon to be created.

I understand that this can be seen as a classical or as a quantum phenomenon and so I would like to understand it classically in as microscopic a way as possible and then to try and understand it in the Quantum explanation (although I anticipate this as  being very challenging  for me)

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Physics, Astronomy & Cosmology / Re: Does gravity attract masses in space, or does it curve space between them?

« on: 27/05/2020 00:28:42 »

There is no spacetime curvature in a uniform gravitational field. It's a myth that all gravity is a curvature in spacetime. Curved spacetime is the same thing as tidal forces and a uniform gravitational field has no tidal forces.

What might be an example of a uniform gravitational field?

The surface of a sphere  with all the mass at the centre?

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Physics, Astronomy & Cosmology / Re: Does gravity attract masses in space, or does it curve space between them?

« on: 26/05/2020 03:25:37 »

It can do both. BTW you're referring to spacetime curvature, not space curvature. You can have a gravitational field without spacetime curvature. An example is a uniform gravitational field. Spacetime curvature is the same thing as gravitational tidal forces. A uniform gravitational field has zero spacetime curvature,

That is interesting.Could you expand on that at all?
How would a uniform gravitational field manifest its quality of producing no spacetime curvature?

Would there be any other effects that would distinguish it from what might be described as a  concentrated source of gravitation?

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Physics, Astronomy & Cosmology / Re: Did Einstein "kick the can" on gravity?

« on: 21/02/2020 01:50:20 »

As Alan says the field is a mathematical abstraction. What you do is place a test mass (1kg) and measure the force vector acting on that mass, that vector is the field strength (unit gravitational force) at that point (you can do the same with a magnetic field, using a test magnet). In this case you create a map of of gravitational force values for a volume of space.
That’s all a field is. The value of it is that with gravity we can use a simple formula to calculate the field strength at any point between 2 masses, and hence the force between 2 masses.

Is that the famous Einstein Field Equation I have heard of?
 (if it is I am glad to learn it is simple    )

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New Theories / Re: Troll theory: How does gravity work?

« on: 19/02/2020 15:48:29 »

General relativity doesn't explain gravity , it explains an effect of gravity which is space-time curvature .

Newton explains gravity in basic detail correctly as a linear force between masses . This linear force of gravity of mass curves space-time energy by applying a linear force on the tensor linear force of spatial fields , hence curving the fields towards the mass .

Additionally a proton has a positive charge and an electron a negative charge , the existence is already cataloged

Does your suggestion make any testable predictions that differ from those made by General Relativity?

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Physics, Astronomy & Cosmology / Re: Did Einstein "kick the can" on gravity?

« on: 19/02/2020 14:55:17 »

You can feel a gravitational field. Lead is much more susceptible to gravitation, and hydrogen much less so,  than human tissue. You can also sense the absence of a gravitational field by jumping out of a plane

So it is perfectly acceptable to think of the field as a physical object that is subject to deformation? Is it a 3d +1 physical object?

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New Theories / Re: Troll theory: How does gravity work?

« on: 19/02/2020 14:25:08 »

A positive charge is attracted to a negative charge and vice versus .

When a positive charge and a negative charge are converged to form a neutral charge measure , the convergence forms a weak force namely gravity . A neutral mass attracts both negative and positive charge , a neutral mass also attracts other  neutral mass but with less acting force as the convergence of pos and neg creates an equilibrium of forces .

This does not sound to me like the current theory of General Relativity.I am not aware that a positive or a negative  gravitational charge has ever been isolated.

Have you any documentation that does show this ,or ,failing that why  they exist despite not being shown experimentally to exist?

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New Theories / Re: Troll theory: How does gravity work?

« on: 19/02/2020 13:45:58 »

The mechanics of gravity is : The positive and negative charge of matter is attracted to other positive and negative charges of other matter

I thought these did not exist .Can you show how they  do?

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Physics, Astronomy & Cosmology / Re: Did Einstein "kick the can" on gravity?

« on: 19/02/2020 13:08:40 »

If we  consider gravitation fields to actually  be physical objects  in the same way as magnetic fields are  ,can we say that mass/energy distorts  these fields?

If that was so it would put to bed the head scratching that goes on when people try to visualize space or spacetime being somehow physically curved when ,intuitively that just feels absurd.

I know that gravitational fields are very different from magnetic fields and it would be difficult /impossible to feel them in the same way because  everything is subject to gravitational fields .( you can feel magnetic fields because the human body is less subject to that field than ,say a metallic object it might hold in the hand. )

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Physics, Astronomy & Cosmology / Re: Did Einstein "kick the can" on gravity?

« on: 12/02/2020 16:05:47 »

When people talk about an ‘actual mechanism’ they are missing the point. GR provides the mechanism, the very fact that the spacetime dimensions are not ‘flat’ as we might expect is the mechanism and it is well described in the field equations. I think @Janus has described it elsewhere.

So not so much a mechanism as a basic condition ("flat space" is just a special case  that applies when  there are no local sources of gravity and the "natural" condition  is just a function of the local distribution of energy)

But if we do not have a theory of Quantum Gravity does it not follow that there are mechanisms involved in spacetime curvature  yet to be explained?

E.g. we don't know yet ,do we whether spacetime should be  a continuous or a discrete model ,do we?

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Physics, Astronomy & Cosmology / Re: What's wrong with the gravity analogy?

« on: 12/02/2020 15:31:55 »

not sure what you mean, can you expand?

I have been thinking about this.I am handicapped by my lack of knowledge in this area but I will have to try and explain what I  may have been  thinking.

Time seems to me like it could be more fundamental than spacetime (space/distance  perhaps ,also)

I know Minkowski said that henceforth we should consider spacetime rather than space or time independently and of course that has led to predictions that we wouldn't have otherwise.

But I am wondering whether ,in some way spacetime  might have emerged from space and time  and that space and time do/did have independent existences before we had the spacetime that we now observe.

Of course ,if spacetime is completely fundamental  then I would accept that but is it accepted generally that it is the case? Do all  potential theories of Quantum Gravity approach spacetime ,time and space in the same way as current classic and quantum theories do?

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Physics, Astronomy & Cosmology / Re: Did Einstein "kick the can" on gravity?

« on: 12/02/2020 11:17:00 »

we still don't know why massive bodies attract each other, or, if you prefer, always warp spacetime in the same sense

Is it a good starting off point to take it as axiomatic that the "natural" relationship between relative  space measurements and time measurements   is variable ?

Would that take us any further towards detecting the actual mechanism(s?) that caused changes in that variability?

To the OP I think it was probably in Einstein's character to kick the can down the road and continue running after it.

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Physics, Astronomy & Cosmology / Re: Did Einstein "kick the can" on gravity?

« on: 10/02/2020 17:02:59 »

It's the best we had, until the discovery of gravity waves. Still no evidence of a particle, but you are welcome to join the search.

I thought Einstein predicted gravitational waves...just thought we would never detect them.

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Physics, Astronomy & Cosmology / Re: What's wrong with the gravity analogy?

« on: 10/02/2020 12:33:42 »

 

Why would you assume that?

Janus was describing how space and time are inextricably linked, movement through one affects movement through the other (relatively)

Well "the natural tendency for things to go from past to future" as Janus described it  seems to involve phenomena
(a phenomenon) that lie outside the spacetime model .

I mean ,the spacetime model would ,I suspect work as well if time ran backwards ,but I think we are taking it as an axiom that time runs in the direction of increasing entropy.

That is why I was wondering if this question of the "mechanism" of the unfurling of time (eg its direction) might be more fundamental than the outworkings we see in the spacetime relativistic effects when relative distances become involved.

I notice you seem to talk of things moving through space as well as through time (in their inter related way) but wonder can we really talk of things "moving through space" when all they are doing ,arguably is to change their positions  relative to each other and not "through" anything

I am musing rather than prescribing

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Physics, Astronomy & Cosmology / Re: What's wrong with the gravity analogy?

« on: 10/02/2020 00:55:43 »

One way to look at it is that in curved space-time, the natural tendency for things to go from past to future is partially transformed in a tendency to move towards a lower gravitational potential. In other words, movement through time becomes spatial movement to a certain degree.

By describing a "natural tendency for things to go from past to future" are you in any way saying that there is an absolute nature to time ? It sounds to me as though time is primordial and that space-time  is  something  that developed from it

Are you saying ,or implying that this attribute of time is ever present(an odd choice of words on my part)  and somehow independent of space-time itself (well space-time is just  a  highly successful model,I think I have heard)

Time is perhaps no model ,whereas space-time is?

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Physics, Astronomy & Cosmology / Re: Is the equivalence principle only approximately correct?

« on: 11/01/2020 14:24:27 »

Just as a historical note, since we went into space the mechanics of low gravity environments  (and artificial gravity) have become second (almost first) nature to us.

Was it surprising that Einstein (and  others,perhaps?) seems to have "twigged" gravity without the advantage of these  very elementary first hand observations?

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Physics, Astronomy & Cosmology / Re: Is the equivalence principle only approximately correct?

« on: 11/01/2020 01:26:04 »

Thanks.I think you have addressed my concern.

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Physics, Astronomy & Cosmology / Is the equivalence principle only approximately correct?

« on: 11/01/2020 00:44:27 »

I have been reading E's Popular Exposition of SR and  GR (it is for the layman and so I may be reading too much into what may be relatively simplistic scenarios) and the following "objection" to his closed room experiment occurred to me.
The gist of his argument seems to be that an observer in a sealed container  will not be able to tell if he or she is being accelerated or experiencing gravity.

However  ,if the propulsion is being caused by a rope tugging a hook in the centre of the ceiling it would be possible by  examining the ceiling to verify that the force is in fact being directed at that particular area (the room cannot be 100% rigid) and so it is possible to distinguish between a gravitational  effect vs acceleration.

If the room was vanishingly small (Or completely rigid) this would indeed  then be impossible.

Am I right or just being pedantic? (Or misunderstanding the scenario in the round?)

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Physics, Astronomy & Cosmology / Re: When did gravity begin?

« on: 14/12/2019 14:34:41 »

I don't even have a picture of gravity with a Higgs field.

Sorry, I should have said "rough description" rather than "picture" (but you perhaps  knew that and gravity pre Higgs  may be entering uncharted waters? Quantum Gravity territory?)

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Physics, Astronomy & Cosmology / Re: When did gravity begin?

« on: 14/12/2019 11:40:50 »

Gravity is posited to exist before anything else.  The earliest meaningful epoch is the Planck epoch, up to 10^-43 seconds, where the universe consisted of a 'gravitational singularity', which wasn't specifically gravitational since the four fundamental forces had yet to separate.

In the next 10^-36 seconds, gravity separates from the other three forces.  This is all before the inflation epoch where expansion takes place oodles faster than it does thereafter.

The Higgs field seems to come after the inflation as the strong force separates and the Higgs field confers mass on the various particles forming.

So is there any picture of what gravity (that is synonymous with spacetime ,I have been told) would look like without a Higgs field?

Anything else to say about "gravitational singularity"? Is it "singular" in any other sense?