John Duffield
  • Member for 6 years, 10 months
  • Last seen more than a month ago
Work done in assembling a point charge is infinite
8 votes

Griffiths was referring to "the problem of infinities". See the Wikipedia article on the history of quantum field theory which has a section on it here. People often say this issue stemmed ...

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Are the relativistic effects of gravity strictly due to spacetime 'curvature'?
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0 votes

I happen to live on an infinite flat Earth. It has a constant uniform gravitational field extending above it. It's an unrealistic scenario, but I'm sure we've all heard of it. If the massive body is ...

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Can gravitational waves carry momentum, and if so what mass/energy produces it, and is space-time capable of vortex formation?
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1 votes

Is gravitational radiation a form of mass/energy that can form momentum? We think so. We haven't detected any gravitational waves as yet, but there's a high degree of confidence that gravitational ...

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Queuing by the event horizon
-12 votes

I understand that an observer outside the event horizon (EH) of a black hole (BH) will not see anything disappearing from outside the EH - only the effects of the time dilution near the EH. He'll see ...

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Is the energy density of vacuum uniform in the whole universe?
Accepted answer
-2 votes

Is the energy density of vacuum uniform in the whole universe? No. It varies in a gravitational field. That's why Einstein said “the energy of the gravitational field shall act gravitatively in the ...

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How can beta plus decay be possible?
-2 votes

How can beta plus decay be possible? Because it isn't really a decay. At least, not like beta minus decay is a decay. That's where you start with a neutron, which is perhaps a free neutron. Without ...

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Is Supersymmetry really swapping fermions with bosons?
-1 votes

Is Supersymmetry really swapping fermions with bosons? I wouldn't say supersymmetry is really swapping fermions with bosons. It's saying there's a certain symmetry wherein each particle has a ...

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Would possibility of instant communication break physics?
-2 votes

Would possibility of instant communication break physics? No. Not at all. I recently read a sci-fi book, where some (very few) people can communicate telepathically, which happens to be ...

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How can we relate the idea of flux with electric field
-3 votes

How can we relate the idea of flux with electric field I don't think you should. I think it causes confusion. Doesn't flux mean the measure of flow of something represented by vector A. But in ...

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How much of the proton's mass is due to the Higgs field?
-8 votes

How much of the proton's mass is due to the Higgs field? My view on this is coloured by Gian Francesco Giudice’s 2010 book A Zeptospace Odyssey. On page 173 he said this: “The most inappropriate name ...

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If you could bottle a photon would it have mass?
1 votes

If you could bottle a photon would it have mass? I'd say the photon itself wouldn't, but the "system" would have extra mass, yes. Ok. A photon has no rest mass for the good reason that it has no ...

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What is time dilation really?
5 votes

What is time dilation really? A reduced rate of local motion. See What is time, does it flow, and if so what defines its direction? As Einstein said, time is what clocks measure. And if you take a ...

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What is time, does it flow, and if so what defines its direction?
19 votes

What is time? As Einstein said, time is what clocks measure. And if you take a look at what a clock actually does, if you open up a clock and take a cold scientific look at the empirical evidence, ...

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Why is analyticity a good mathematical assumption in general relativity?
-10 votes

Why is analyticity a good assumption in general relativity? It isn't. In general relativity, real-variable analytic continuation is commonly used to understand spacetimes. For example, we use it ...

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Does acceleration in free fall disprove Newtonian mechanics?
-4 votes

Does acceleration in free fall disprove Newtonian mechanics? No. It shows that it doesn't always apply the way that you think. In Newtonian mechanics, how come the net force on an object in free ...

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What is the geometry of DeBroglie standing waves?
-2 votes

What is the geometry of DeBroglie standing waves? Toroidal. Or should I say the topology is toroidal whilst the geometry is spherical. See Is the electron a photon with toroidal topology?. It was ...

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Interpretation of the Raychaudhuri equation and the attractive nature of gravity
-6 votes

In many books it is stated that the Raychaudhuri equation is a sort of "proof" that in general relativity gravity is attractive. T An equation doesn't really prove anything. And since it's "important ...

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Speed of light in a perfect vacuum
-4 votes

Let's say that something is in a universe with a perfect vacuum, where nothing exists but that object. This universe has an infinite amount of space and time. Now that object emits a single photon. ...

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Zero-level of combination of $1/r$ and $r^2$ potential
-7 votes

I am solving a problem which involves a central big mass $M$ and around it a spherically symmetrically distributed mass of constant density $\rho$. The force on a mass a distance $r$ from the ...

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Interpretation of the nature of light in quantum mechanics
-3 votes

Maxwell's theory of electromagnetism describes light as a wave of the electromagnetic field. Yes it does. Quantum mechanics associates a probabilistic wave (my own interpretation of the function ...

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Where does stuff "sucked" up by a black hole go?
1 votes

Where does stuff sucked up by a black hole go? Into the black hole, increasing its mass. I've heard that stuff sucked up by a black hole leads to a parallel universe, but I don't believe that. ...

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Contradiction between Geroch's theorem on topology change and formation of naked singularity?
-4 votes

It's been known since Oppenheimer and Snyder's work in 1939 that it's easy to get a naked (i.e., timelike) singularity in models of spherically symmetric gravitational collapse, for forms of matter ...

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Breit–Wheeler γ γ′ → e+ e− pair production with hohlaraum as photon target; is this particular experiment going to be carried out?
0 votes

Work is in progress. See Experiments underway to turn light into matter on the Imperial website: In laser facilities in the UK, Imperial physicists are testing an 84-year-old theory which was once ...

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Any photon colliders in the past?
1 votes

It was done at SLAC in 1996. See Positron Production in Multiphoton Light-by-Light Scattering. The paper was in Physics Review Letters. For some background reading, there’s plenty of arXiv papers ...

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Is absolute zero possible in a complete vacuum?
-7 votes

Is Absolute Zero Possible? Yes. In a black hole. Thermal energy is the energy an object due to the motion of its molecules. This means as long as an objects molecules have kinetic energy, it will ...

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How “wide” is a beam of light? What is its half-diameter?
-3 votes

How “wide” is a beam of light? It doesn't have a width in the usual sense. I know that sounds odd, in that you can see a beam of light in a dusty room, and if the gap in the blinds in 1" wide, the ...

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Do photons slow down?
-2 votes

Do photons slow down? Yes, a photon moving downwards slows down. If it reflects off a mirror on the floor and then moves upwards, it speeds up. Not many people know this, but it is true. See Is The ...

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Is the vacuum energy density proportional to the scale of the universe?
-2 votes

Is the vacuum energy density proportional to the scale of the universe? I think it does. I do not buy the assertions that claim it's constant, and that energy is being created as the universe expands....

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Where can a mathematician read Hawking's proof for the existence of a black hole's radiation?
0 votes

Where can a mathematician read Hawking's proof for the existence of a black hole's radiation? IMHO the first port of call is his papers. Hawking’s first paper on Hawking radiation was arguably the ...

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Give an interpretation of what $c=\frac{1}{\sqrt{\varepsilon_0\mu_0}}$ actually means
1 votes

From my later school days on, the formula that impresses me the most is $c=\frac{1}{\sqrt{\varepsilon_0\mu_0}}$ IMHO it's nothing special. All it's saying is that the speed of an electromagnetic wave ...

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