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Strange

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Strange last won the day on September 5

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About Strange

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    珈琲店
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    Physics
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    Engineer/Writer

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  1. Good article on everything we know and don’t know about dark matter here: https://www.forbes.com/sites/startswithabang/2019/09/19/was-dark-matter-really-created-before-the-big-bang/
  2. ! Moderator Note Because it is science fiction. That is not a suitable basis for scientific speculation.
  3. No you would not. In fact dark matter is passing through you all the time (although the density of dark matter around the Earth is very low). Just like neutrinos. It would be invisible, because it doesn't interact with light.
  4. That may have changed and, in some cases reduced, some forces of selection but it certainly hasn't removed humans from natural selection.
  5. There are multiple lines of evidence for the existence of effects caused by something we label "dark matter". These include the orbital speeds within galaxies, the speeds of orbits with galaxy clusters, gravitational lensing, the spectrum of the CMB, the formation of large scale structures in the universe, and probably more. Nearly all of this evidence points to dark matter being a form of matter which does not interact electromagnetically. So, similar to neutrinos but it must be more massive because the distribution shows it to be moving more slowly. Not "see" it because it doesn't;t interact with light. I guess the question means will we ever have a more "direct" detection of the particles that make it up? Probably. It took over a decade to detect neutrinos "directly" before they were first detected. Obviously, it is harder to detect dark matter particles (otherwise we would have known what they were, perhaps even before observing the effects). It is rather inevitable that each new type of particle is going to be harder to detect. I don't know what that means. Neptune was a "wildcard thrown in to a mathematical equation to make the equation work". The same could be said of electrons, photons, gravity, energy ... Physics is described in terms of equations. When we discover new things, they are are included in those equations. That would be true whether dark matter is a modification to gravity or some form of matter. So the question doesn't really make sense.
  6. The only force present is gravity, which acts downwards. So you are right that the reason the relatively less dense air goes up is because the denser cold air is pulled down. This is basically the same mechanism for hot air balloons going up or for bubbles rising through water.
  7. Not really. SR is just a subset of GR that can be used under certain conditions (when the system can be approximated by an inertial frame of reference). The GR definition if more generic (because it is the general theory of relativity). While the SR definition is a special case of that.
  8. ! Moderator Note Passenger, you have not explained what this thread is about, you have not answered any questions and your use of English is so idiosyncratic that it is almost incomprehensible. ! Moderator Note It would be better to use the Report function for this sort of comment to ensure it is seen by the moderators. If you think the other thread is worth continuing, please report it and make a case for keeping it open.
  9. If you don’t have access, you could try your local university library
  10. I think you would have to look in some journals, find papers about the measurement of the value, look up the references in those papers, and so on, to track through the historical measurements. This would probably be a good place to start: https://iopscience.iop.org/article/10.1088/0034-4885/76/1/016101
  11. Another (slightly more detailed) article here: https://www.quantamagazine.org/physicists-finally-nail-the-protons-size-and-hope-dies-20190911/
  12. ! Moderator Note You were told not to bring this up again.
  13. It is exactly that. The m is the rest mass, so there is no kinetic energy. So "all E except KE" = "all E". The equation for a moving object is: [math]E^2 = (mc^2)^2 + (pc)^2[/math]
  14. "we can observe galaxies that have, and always have had, recession velocities greater than the speed of light." https://arxiv.org/abs/astro-ph/0310808 That is assuming an expanding universe. It isn't clear if the OP is trying to deny expansion. But if so, it wouldn't be possible for galaxies to be receding faster than light.
  15. That has been known for a long time. I'm not sure how it is relevant to this thread. As kinetic energy, in the chosen frame of reference. It has nothing to do with "Einstein's logic". That could be totally wrong. It doesn't affect the validity of the theories.
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