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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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    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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    I Conservation of momentum in a collision

    Now, deriving relativistic momentum isn't terribly difficult, but that's not the same as understanding it. I'm trying to figure out why conservation of momentum in special relativity requires the gamma factor. When I looked at conservation of momentum in elementary physics, we basically just...
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    Found the EFE in Iron Man 2

    Nice little Easter Egg. It’s about one hour and thirteen minutes in. I wonder if there's any comic book cannon about arc reactors having something to do with spacetime?
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    COVID Is what’s happening with the flu an example of Competitive Exclusion?

    COVID-19 is thriving, while reported influenza infections are at record lows. As someone untrained in biology, I’m probably off the mark, but that sounds to me like an example of competitive exclusion. COVID-19 has a potentially longer incubation, it’s more contagious, people can be asymptotic...
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    I "Leading clocks lag" twin paradox

    . . Two distant observers at rest with one another synchronize their clocks utilizing the travel time of light (by first moving the clocks to their locations, then using a light signal to time when the second clock should be turned on, and setting the second clock ahead to account for the...
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    I Regarding i^2, and why it's -1 and not 1

    So presumably ##x = \sqrt{-1}## can be derived as a solution to the equation ##x^2 + 1 = 0##, thus, ##x = ± \sqrt{-1}## (1) We always use the positive root. What is the reason for that? Is it simply a convention? Or are there dire consequences for using the negative root, such as causing the...
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    COVID Anyone else having a terrible reaction to the COVID vaccine?

    Man this is killing me (figuratively I hope). I know I’m whinging, but I rarely get sick, and here I am experiencing full on flu symptoms along with a slightly discomfortable chest after the 2nd Pfizer. In addition to the sore arm. Being sick sucks, especially when it’s fake sickness meant to...
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    I Are tidal forces just curvature of space?

    I've heard it and I've read* it before, so I just want to make sure I understand this so I never have to wonder about it again. So, are tidal forces exactly curvature of space? Here's why I think the answer to that is yes: . I've seen a spacetime interval equation which has a coefficient on...
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    I How quickly do electrons jump orbitals?

    I would hope something like this would come in handy: ΔEΔt>h/2π. Mainly because it seems relatively simple, although I'm not really sure what the inequality really means, other than there is a certain uncertainty associated with that pair. But there are some things that really muddy the waters...
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    Optics question: Looking at mirrors from parallel to the surface

    I did a little experiment recently where I took a plane mirror and held it underneath a ceiling light. Then, I began to lower my head so that my view was closer and closer to the surface. When I did this, the image of the light began to drift lower and lower in the mirror until it completely...
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    B Realistic window view from a starship

    I have my own intuition on things, which I hope to correct if I’m wrong. For example, the most obvious thing is that stars won’t fly in a straight line from the front of the craft to the back if you look out the side window because the craft would be rotating to simulate Earth’s gravity. So...
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    B The basics of spacetime diagrams

    Spacetime diagrams seem to be the most used explanation for relativity weirdness, so I’d like some clarification in how to make them, it anyone wants to help. (1) Light’s worldline is 45 degrees, obviously. No issues there, I don’t think. (2) How do I determine the angles of the moving frame...
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    I Alcubierre drive and gravitational waves

    Suppose some aliens travel to our solar system after seeing our radio broadcasts using an Alcubierre drive. Would it not create a notable gravitational disturbance? Or does it leave spacetime undisturbed around it?
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    I Is this a correct understanding of the pole-barn paradox?

    I want to make sure I have this right, and whatever I have wrong I would like to fix it. Part I: So in particular, I’m referring to a fast moving pole along the x-axis of an observer who is at rest with respect to the barn (the barn is a few feet away from the observer), and when the pole is...
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    I Skipping elementary calculus and starting at analysis?

    I was walking around with my head in the clouds and suddenly I wondered if a smart person, say, a philosopher, could start at the full monster of real analysis instead of elementary calculus. Would there be any hope for this unfortunate soul? What are your opinions and why? Or if you feel this...
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    I Motion through space and time once you cross the event horizon of a black hole

    Tad Williams’ Otherland series has a scene where the characters are drawn to a temple no matter which direction they try to walk, as if space itself is curved. This is kind of the intuition I get when a physicist talks about the spacetime interval kind of flipping past an event horizon: if you...
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    Is there a clever name for Newton's 2nd Law?

    Summary:: We all know of the "law of inertia" nickname for Newton's 1st law, but is there a clever name for the 2nd as well? What about the 3rd? This may be the most inane question ever asked here, but I've spent some time searching and cannot find an answer. So many laws in physics and other...
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    I Why does an object initially at rest begin to fall?

    Motivation for why I'm asking this: I'm trying to better understand why an object that is initially at rest with respect to a massive body will fall simply by virtue of the curvature of spacetime. If it were moving through space with respect to the Earth initially, I could see the curved path...
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    I Can Newtonian gravity be thought of as a theory of curved time?

    Before I attempt to delve into the math of tensors and curved spacetime, I'm hoping to get a more general intuitive grasp of things. As such, I'm parsing through a lot of lower level articles on these topics, and several that I've come across have argued that Newtonian gravity can be thought of...
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    I Do you accelerate through time when you stand still on Earth?

    Disclaimer: I'm not actually sure which acceleration is proper and which is coordinate, and I can't recall the source for the half-remembered equation. I spent some time going through my bookmarks, but it was to no avail. Sorry about that. So, general relativity removes the idea of gravity as...
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    Bubbles in a falling glass of champagne

    Suppose you just poured a glass of champagne, then you drop the glass straight down (so that there is no tilting). Do the bubbles: (1) Continue to rise with respect to the glass. (2) Remain in place with respect to the glass. (3) Sink with respect to the glass. My intuition is telling me...
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    Does inertia have anything to do with bodies falling at the same rate?

    The equation manipulation that shows that bodies will fall at the same rate regardless of their mass is very straight forward, because mass cancels when you set F = ma of the body equal to gravitational force using Newton's gravitational equation. I have no problem understanding that in terms of...
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    A Can an object be at rest in its own reference frame?

    In classical physics, every object is obviously at rest with itself, and it makes perfect sense for this to be true. But would this violate the uncertainty principle for a particle? If you are the particle and you know that you're at rest with respect to yourself, you know both your location...