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    I Falling into a black hole: blueshift questions

    Okay so back to tidal forces and size: Am I mistaken that being close to a super massive black hole you’d feel gentler tidal forces than close to a stellar mass sized black hole? What about if you were at the event horizon for each?
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    I Falling into a black hole: blueshift questions

    Ah yes, of course, you measure it, thus it is not coordinate dependent. So, as you cross the event horizon, blueshift at best would be moderate. Does this also depend on the size of the black hole? I am under the impression that tidal forces depend on the size (if altitude is the same, larger...
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    I Falling into a black hole: blueshift questions

    I am under the impression that an outside observer would see things redshifted as the person they are observing approaches the event horizon. So, it seems reasonable that someone from inside the black hole would see incoming light blueshifted. Is this inaccurate? Why or why not? If it is...
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    COVID Reaction to COVID-19 Vaccine (or what to be prepared for)

    Perhaps, but look at the world we live in today. What was fringe fifteen years ago is now proudly shared online, and millions get their minds infected with things like flat earth stupidity, QAnon stupidity, and on and on. We used to laugh at conspiracy theorists. Now they are making public...
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    COVID Reaction to COVID-19 Vaccine (or what to be prepared for)

    There is one and only one type of source anyone should be trusting or posting here, IMHO: peer reviewed scientific publications.
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    I Black hole inside of a black hole... can it be done?

    This is excellent stuff. But since @mitochan brought up colliding BHs, I have a related follow up question: Nothing can travel faster than c, so would this not prevent two colliding BHs from ever instantly becoming one? Because presumably the two singularities are separated by a non-zero...
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    I Black hole inside of a black hole... can it be done?

    Let's say you have an absolutely giant black hole, so big that items inside of it leisurely approach the singularity, reaching it in about a million years (or whatever time it takes for a black hole to form from matter accumulation). Could matter slowly accumulating somehow form its own black...
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    COVID Reaction to COVID-19 Vaccine (or what to be prepared for)

    Kind of makes you wonder why this isn’t being done already given it’s supposed to be intramuscular. Is it particularly time consuming? I wouldn’t know. EDIT — upon reading more, it seems the concern isn’t enough to make it a widely practiced part of IM injection.
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    B Why does it require an infinite amount of energy to reach the speed of light?

    I myself have wondered if that's even physically possible, with all the quantum weirdness. I'm of course fully ignorant about QM, but the thought has crossed my mind. Not that it matters, since in physics simplifying models are used to isolate particular paths of inquiry.
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    I Conservation of momentum in a collision

    Excellent explanation. Thank you for coming back this. It is interesting, as PeterDonis pointed out in post #42, that you only have two choices. But seeing it this way helps me get a better a snapshot of all the balls that were being juggled by these people early in the 20th century trying to...
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    B Why does it require an infinite amount of energy to reach the speed of light?

    That’s a great Insight, but one thing I’ve wondered is why the concept of relativistic mass was even invented, other than the need to keep equations more familiar. Is there another more useful reason for it being created?
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    I Express the acceleration in terms of force and velocity in SR

    Not with knowledge of the term but I suppose yes. But yeah, as a student I will agree that standard Minkowski diagrams are more intuitive. Loedel diagrams may have some usefulness, but not at the expense of opening the door to more confusion. There’s enough unintuitive stuff to worry about...
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    I Express the acceleration in terms of force and velocity in SR

    Yes. But presumably you could use the simple Pythagorean trig identity by replacing ##γ^{-1}## with ##\frac{1}{γ}## could you not? (I wonder if that would be of use at all) That is, ##γ^{-2} = γ^{(^-1)(2)} = (\frac{1}{γ})^2## ##\beta^2+(\frac{1}{γ})^2 = 1## looks the same to me. But even if...
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    COVID Reaction to COVID-19 Vaccine (or what to be prepared for)

    I was told by the nurse if you’re going to have a dangerous reaction, it’s most likely after. Maybe stay vigilant.
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    I Express the acceleration in terms of force and velocity in SR

    But that surely means you can easily change those to trig functions. I am now intrigued. That negative power raises a small problem, but surely there is a simple work around I’m missing. An i or something.
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    COVID Reaction to COVID-19 Vaccine (or what to be prepared for)

    There’s no way I can remember the study, but I read one that said that while peak viral load was the same for breakthrough cases as it was for unvaccinated, the viral load in vaccinated patients decreased much faster — which indicates they would spread it less over similar time windows.
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    COVID Reaction to COVID-19 Vaccine (or what to be prepared for)

    My guess is that would have been 14-15 had everyone been unvaccinated.
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    COVID Reaction to COVID-19 Vaccine (or what to be prepared for)

    That’s true. Quick general question to the biologists here: If R is reproduction number and E is vaccine effectiveness, does this formula tell the percentage we need to vaccinate to get herd immunity? ##\frac{1 - \frac{1}{R}}{E}## I can’t remember where I’ve seen that but it looks familiar.
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    COVID Reaction to COVID-19 Vaccine (or what to be prepared for)

    All of those studies I clicked on said vaccination reduces chances of infection, some by a very large amount. I don’t understand the hold up here. Also one criticism I have of some studies on the topic is that some rely on patients reporting if they’re vaccinated or not, and I guarantee at...
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    COVID Reaction to COVID-19 Vaccine (or what to be prepared for)

    Breakthrough infections are pretty rare compared to unvaccinated infections based on all the publications I have read.
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    COVID Reaction to COVID-19 Vaccine (or what to be prepared for)

    Meanwhile a serious side effect of COVID 19 is death, and it’s way more common than these serious vaccine side effects.
  22. G

    I Information traveling faster than light? (thought experiment)

    You’re using the Galileo velocity addition formula, which is only accurate for speeds much less than c. https://en.m.wikipedia.org/wiki/Velocity-addition_formula
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    I Conservation of momentum in a collision

    I actually have not at this point, which is weird, given that I have messed around with some of the (non-tensor) math. But that's not physics. I do plan on actually going through some of the problems in that Tipler book (I've actually bought it, so I won't be a total cheap-o and steal from the...
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    I Conservation of momentum in a collision

    Yeah that’s just a writing error. I don’t know if you can see all my edits but I had a nightmare of LaTex issues, which screwed up my proof reading. I was supposed to be copying Tipler and just messed it up. What I’m curious about now, however, is why the choice of units gives a false...
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    I Conservation of momentum in a collision

    Ah. Now that makes some sense. (from Hyperphysics via a google search) Which means it's just a unit coincidence that when written as I written it looks the opposite.
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    I Conservation of momentum in a collision

    Just found another one by Tipler (Modern Physics, 4th ed.) that does something similar, but then it takes it into a direction that seems ripe for confusing me: since each momentum component has its own gamma, it expresses γ in terms of the primed coordinates, so you get γ. $$γ' = \frac{1}{...
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    I Conservation of momentum in a collision

    Oh man I’m sorry. I’ll delete it. Also, in hindsight I can see how this approach is dangerously close to suggesting relativistic mass. Probably not a good approach. EDIT — that text book does mention realistic mass shortly after that example, but then says for the duration of the book mass...
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    I Conservation of momentum in a collision

    The purpose of all this is to trace the train of thought of someone new to the concept of momentum in relativity, someone who's been taught their whole life that p=mu and that this value is conserved, and how they might be convinced on an intuitive level. Someone who isn't well versed enough on...
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    I Conservation of momentum in a collision

    Would you be kind enough to look at my last post? I have rephrased the question again and attempted a physical example to show what I'm hoping to show. Apologies. I completely messed up what I meant to say. What I mean is: (1) Start with ##dx##. (2) Divide by ##\frac{dt}{γ}##. That gives...
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