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This sentence makes no sense, since gravity is a phenomenon, not a thing (like matter) that can interact. Unlesse what you had in mind is gravitons, but then I'm not sure it is true that they don't interact electromagnetically.

No because dark matter does not interact electromagnetically (per definition) so it cannot form atom-like systems.

He did not as I've already explained. Stop misstating this paper.

Maybe some high school math and basic calculus but even then not everything you can practice with repetition. In general math needs as much of deep understanding as physics. During my studies at Warsaw University most of first year students failed because of math. I would say that high school...

Well, in a way they constitute spacetime. And since gravity can be thought of as geometry of spacetime, and since you've said that you see how spinfoams and networks are related to spacetime, then I guess that would mean that you should see how they are related to gravity :tree:

What is gravity in the context of classical GR?

It's not: https://en.wikipedia.org/wiki/Geodesic

We do? o0) I did not learn about it, no one ever even wanted me to know how to convert between Fahrenheit and Celsius. I guess it depends on the country.

I said textbooks, not pop-sci books.

They did not write those thing in their textbooks nor peer-reviewed papers. Pop-sci sources are not bases for scientific discussion.

Quantum particle which is neither classical particle nor classical wave. Wave-particle duality is an outdated concept - use search button for other discussions of this issue, since its been beaten to death here.

No and no. For reference see any QM textbook.

Can you provide a reference that states that there is no way to test entanglement by its very definition? If not then I don't see any connection to the one way speed of light.

Which exists only in non-inertial frames. I find it risky to explain things by using inertial forces because people usually don't understand them properly.

No, and if the OP needs to read more on that I recommend this insight: https://www.physicsforums.com/insights/what-is-relativistic-mass-and-why-it-is-not-used-much/

Based on the solution provided by the author - nothing.

Figure 4, shown from a bird's eye view, shows traces of smoke from the chimneys of two ships, which are sailing in opposite directions through the canal connecting two lakes. Determine the wind direction if the ratio of their speeds is: ##\frac{v_1}{v_2}=\frac{3}{5}##. I've actually searched...

There were actually two boats traveling along a canal that is joining two lakes (sorry, I rarely use words "river" and "lake" and I mix their meaning) - see attached picture. Ratio of their speeds is ##\frac{v_1}{v_2}=\frac{3}{5}## and one has to determine direction of the wind. The only...

Since my assumptions regarding behaviour of smoke were wrong, I guess it doesn't matter :blushing:

Well, I assumed that smoke released at a point on the arc moves with constant speed (equal to speed of the train) along the tangent but now I see that this was bad assumption 😷 Thanks guys! Funny enough, I did quite similar exercise with boats on a river not so long ago and I didn't make that...

Hi everyone. My high-school student got the following homework exercise at school which I have problem with: Smoke from the steam locomotive is carried by horizontally blowing wind. Shape of the smoke trail is shown in the attached figure. Using the drawing, determine velocity of the wind...

No and unfortunately I think this sentence is just a word salad :sorry:

Yes. In that case (##p## is electrons initial momentum, ##p'## is its final momentum): Energy conservation: ##\sqrt{m^2c^4+p^2c^2}+\frac{hc}{\lambda}=\sqrt{m^2c^4+p'^2c^2}## Momentum conservation: ##p+\frac{h}{\lambda}=p'## Squaring both we get...

Please define "physics explanation".

Because you can choose reference frame where it has relativistic velocity. We choose it's rest frame for simplicity. Also, it can have relativistic velocity after scattering so you have to treat it relativisticly from the beginnig. Then you have to include its momentum and energy (total, not...

It is because photons are involved and photons are ultra-relativistic. Treating half of the system non-relativisticly and other half relativisticly won't give you proper resoluts. And I don't even see why one would want to do that in that case. I don't know what you mean by that. ##mc^2## is...

What's funny about that? It's non-relativistic.

Because photons move with speed c in every inertial frame. So in the frame of photon it would be at rest and at the same time it would be moving with c. That's a contradiction, hence there is no raference frame in which photon is at rest.

And there is no such thing as a "point of view of a photon" since there is no reference frame in which photon is at rest.

Besides, light is not a stream of photons the way river is a stream of water molecules. If you are not talking about quantum "situations" you should stick to classical picture of electromagnetic waves.