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New Theories / Re: Does a photon have inertia?

« on: 04/03/2017 18:01:06 »

I note pmb's answers above.

From the above discussion, I take it that:

A photon has an "inertial mass", which equals its "gravitational mass", and is equal to E/c² = hf/c²

Yes.

A photon has momentum = mc = E/c

Yes, but we normally say p=hf/c.

A photon falling into a gravitational well gains energy and inertial mass (and the opposite when it leaves)

No. It doesn't gain energy or inertial mass. Conservation of energy applies. If you send a 511 keV photon into a black hole the black hole mass increases by 511 keV/c˛.

A photon passing by a gravitational well is deflected due to the curvature of spacetime.

No. It isn't deflected by the curvature of spacetime. Spacetime curvature relates to the tidal force, not the "force" of gravity.

This affects the photon's velocity (a vector which includes direction), but not its speed (a scalar which is constant c in a vacuum).

No. The speed of light is spatially variable, and because of this the photon changes direction. See EInstein saying it here:



Inertial mass is also a scalar, and ignores direction.

Yes.

When a photon "leaves" a gravitational well, it has the same inertial mass as when it "entered" (...to the same distance, in the frame of reference of the massive object)

Yes.

Some of the photon's momentum can be transferred to other objects (eg electrons, in Compton scattering). This reduces the photon's momentum and inertial mass by reducing its frequency, but not changing its speed.

Yes.

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New Theories / Re: Where does the kinetic energy go?

« on: 03/03/2017 18:05:29 »

IMHO it's an unfortunate convention that gravitational potential is set to zero at infinity and negative at the surface of the Earth. This negative is not a true negative, in that there are no things that exist that are comprised of negative energy. Instead a body has less mass-energy at a lower elevation, hence the mass deficit. It doesn't have the same mass-energy plus some magical mysterious negative potential energy.

Unfortunately some people promote bad physics. The one that I particularly dislike is gravitational energy is negative so the net energy of the universe is zero. This is pseudoscience, particularly since gravitational field energy is positive. See Einstein saying as much here: "the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy". 

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New Theories / Alternative discussion - why is the speed of light independent of inertial frames of reference?

« on: 01/07/2016 13:47:23 »

So I understand the Michelson–Morley experiment and its result. I do not question the results of the experiment. I have no problem with Special Relativity. The result of this discovery on its surface does seem to defy common sense. It is the independence of the speed of light from other objects in motion that I believe needs a good solid mechanical explanation.

It's the wave nature of matter. Robert Close explained it well in The Other Meaning of Special Relativity. In a nutshell, we use the motion of waves to define our second and our metre, and then use them to measure the motion of waves. So we always measure the motion of waves to be the same. There's a tautology here, which Magueijo and Moffat described in http://arxiv.org/abs/0705.4507.

Note that electric and magnetic field variations are not generated or altered by each other, instead they are two aspects of the same coin, that being the electromagnetic wave. See Jefimenko's equations for something on that. Also see the Wikipedia electromagnetic radiation article and note this:

"Also, E and B far-fields in free space, which as wave solutions depend primarily on these two Maxwell equations, are in-phase with each other. This is guaranteed since the generic wave solution is first order in both space and time, and the curl operator on one side of these equations results in first-order spatial derivatives of the wave solution, while the time-derivative on the other side of the equations, which gives the other field, is first order in time".

The "electric" wave E is the spatial derivative, the "magnetic" wave B is the time derivative. To appreciate this, imagine you're in a canoe at sea with an ocean wave coming at you. The slope of your canoe relates to E, the rate of change of slope relates to B. But there's only one wave there. Note that Maxwell thought in mechanical terms, and described light as transverse undulations in the same medium that is the cause of electric and magnetic phenomena. That's one transverse undulation, not two orthogonal transverse undulations.

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That CAN'T be true! / The antimatter proton

« on: 09/06/2016 21:19:04 »

Where is all the antimatter?

It's hidden in plain view.

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Physics, Astronomy & Cosmology / Why doesn't the light get out of a black hole?

« on: 02/02/2015 22:36:52 »

You're standing on a gedanken planet holding a laser pointer straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now we make the planet denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. We make the planet even denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. We make the planet even denser and more massive, and take it to the limit such that it's a black hole. At no point did the light ever curve round, or slow down as it ascends, or fall down.

So why doesn't the light get out?

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Physics, Astronomy & Cosmology / Is the universe infinite?

« on: 21/09/2014 17:18:30 »

This came up on a thread about infinity started by jeffreyH, and I thought it deserved a thread of its own.

If you ask around about the size of the universe, some people will tell you about the size of the observable universe. The radius of this is thought to be 46 billion light years. I don't think there's much of an issue with that.

If you then ask about the size of the whole universe, some people will say we don't know. I think that's fair enough myself. However some people will say it's infinite. And on seemingly good authority too. See for example this NASA article where you can read this:

"Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO, Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was known to be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracy and precision. We now know (as of 2013) that the universe is flat with only a 0.4% margin of error. This suggests that the Universe is infinite in extent; however, since the Universe has a finite age, we can only observe a finite volume of the Universe. All we can truly conclude is that the Universe is much larger than the volume we can directly observe."

I have no issue with the universe being flat. But I take exception to the inference that a flat universe is an infinite universe. It's a non-sequitur. It just doesn't follow. This thinking is a bit like measuring the curvature of the Earth, and when you can't detect it, declaring that the Earth is infinite. You just can't make this claim, especially since it's at odds with Big Bang cosmology. The universe can't have grown from a small size to an infinite size in a finite time, and I do not accept that the early universe was already infinite. Particularly since I don't see how an infinite universe can expand - the "pressure" of space would be counterbalanced at all locations. I also think that we can't "truly conclude that the universe is much larger than the volume we can directly observe".

What do you think?