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Sasha [They/Them]

@ Sasha @lemmy.blahaj.zone

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  • Why does acceleration break symmetry in special relativity?

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  • Cool yeah, dug through the maths and took the time to understand the situation you were describing and I understand now.

    I thought you were describing a something else, and then slightly confused myself by only considering the metric and not the global picture. I was trying to abuse some old heuristic techniques and they don't quite work for this case, though it was fine for what I was picturing, where Jane and Alice are symmetric about Bob.

    Thanks for taking the time to convince me.

    Actually reading back over this is hilariously dumb, forgive my bad reading comprehension, that is how redshift works.

  • Why does acceleration break symmetry in special relativity?

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  • Would you agree that, at the moment they pass each other, Alice and Jane would see different points in Bob’s history as being simultaneous in their respective reference frames?

    I wouldn't say that's necessarily true, no. It's only true if their speeds are different, the direction they're travelling doesn't factor into it. In either case, their lines of constant time are the same because space is rotationally symmetric. I'm not thinking of them adjusting their calculations to some "true" sense of simultaneous, if that's what you meant in your edit, because there isn't one by definition.

    And it’s related to distance because the further they are from Bob, the greater the discrepancy in their calculations of Bob’s relative time will be.

    That really depends on what you mean by time shift in your original comment. If you mean the shift in what they perceive as simultaneous, then it's not, but it seemed to me that's what you meant. If you mean the difference in their age then I honestly can't remember how it factors in for the accelerating case, I haven't had to think about SR problems in a while.

  • Why does acceleration break symmetry in special relativity?

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  • I don't think this is true, you're right that what's considered simultaneous changes*, but it's not related to distance and that's not how redshift works.

    At best Alice could use the redshift to work out how fast she's moving relative to Bob, if she's moving towards and away from him at the same speed, she'll always get the same result. She'd actually think the same moments are simultaneous regardless of direction.

    The time difference is only accumulated during her acceleration so it can only be measured during it.

    *but only when her speed is different

  • Why does acceleration break symmetry in special relativity?

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  • If you want to get really technical, it's because the symmetries of the Minkowski metric are the Poincaré group. Which includes only rotations, translations and boosts, none of which correspond to acceleration. Meaning it's inherently impossible to make acceleration look like being stationary because of the geometry of spacetime.

    If Alice flies by Bob at some relativistic speed, then there's a very simple coordinate transform (a Lorentz boost) that flips our perspective to Alice's pov; she's stationary and Bob is moving.

    If Alice were to accelerate and we did the same thing, we'd end up with a "momentarily comoving reference frame," in which Alice is only "stationary" for an instant and Bob is moving at a constant speed as before. Or we could create a non-inertial reference frame which would look nothing like Bob's perspective, but Alice would be stationary.

    Physics in non-inertial frames behaves differently, as a simple example: if stationary (or constant speed) Bob dropped an object while floating in space, it would remain there. If accelerating Alice tried the same thing, it would accelerate away from her. You can test this out in an accelerating car or train or whatever and see that it's fundamentally asymmetrical even before considering SR.

    In terms of things like length contraction and time dilation, these are a little more complicated mathematically, but it's just an extension of the above asymmetry when spacetime is Minkowski rather than Euclidean. The difference in observed time is clear when looking at each person's worldline, Alice's isn't straight like Bob's and so she unambiguously experiences a different proper time and proper length.

    Ultimately this means that even if Alice accelerates then passes Bob at a constantly speed, they'll both see one another's clocks running slow by the same amount, when Alice decelerates and returns to compare her stopwatch with Bob's they'll have very different totals which corresponds to how much time Alice lost during her acceleration.

    My favourite feature of this asymmetry is that Alice could accelerate at a constant rate in her reference frame forever, while from outside she would appear to accelerate slower and slower as she approaches the speed of light (which is famously constant).

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    Permanently Deleted

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  • I've had mixed luck, some just don't work on Linux regardless, legit or cracked, but fitgirl repacks generally work well in my experience.

    I've been unpacking/installing them by adding the setup exe to steam as an external game, enabling proton GE and running the installer. The annoying part is then grabbing the installed files from the steam directory and then adding the gamr exe to steam as a separate thing I can actually launch. I tried normal wine. Normal wine did not work (on my distro at least, it's complicated :/).

  • Comment/Post swiping (for up- and downvotes)

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  • it doesn't work very well when set to votes only either, it barely seems to function at all now...

  • How, exactly, does one make a living as a mathematician?

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  • It's just a regulated amount set by the government of each region, the manufacturers want to make them as profitable as possible, but the regulations say they can only be so profitable. The thing is, if you're losing 2% per game, it doesn't seem like much, but the point of slots is you play a lot of games, people sit there for hours and hours and the machines can run multiple games at once in some cases. You can lose all your money quite quickly.

    I never worked on physical machines so I can't really answer any questions about coins, I just got data sheets with the reels on them and info about stuff like custom rules and bonus rounds.

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    Ah, yes, the effect is made of cause

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  • I can't really see that in the meme, but your explanation makes sense

  • How, exactly, does one make a living as a mathematician?

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  • It depends on the region, we were certifying globally. I don't remember the numbers that well, it was years ago and I only did a few months there, but I think it's something like a 98% return for the player, so if you put $1 in, you get 0.98¢ back on average.

  • No comment

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  • Very sarcastic comment, but if the traffic is bad enough then it becomes safe to cycle again because of how little anyone in a car can move.

  • Australia’s Social Media Ban Was Pushed By Ad Agency Focused On Gambling Ads It Didn’t Want Banned

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  • I mean yeah, that makes sense. The Labor government has been up for sale for years

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    Ah, yes, the effect is made of cause

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  • Is it meant to be "that would exist" or is this a pro-colonisation meme? (I know little about the Romans, if I'm just misunderstanding something)

  • How, exactly, does one make a living as a mathematician?

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  • I very briefly had a job as a mathematician for a company that certifies pokies (slot machines). I was technically also a software dev, but my job mainly consisted of calculating the theoretical average returns for each machine, writing basic code to simulate the machine for millions of games and then making sure those two numbers matched. I'd pass that on to a physical testing team who hack them to run real games.

    It was a horrible fucking job and I got out basically a month after I finished my training. All we did was prove the machines were exactly as profitable as allowed in whatever location they were going to be deployed at...

    Now I work as a regular software developer and it's also a horrible job.

  • Collecting Unruh effect particles

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  • Yeah that's why I said they hadn't done work before they collect the particle, I assume capturing it will involve some transfer of energy but again it depends on the experimental setup.

    Very unsure of this, but I believe there's relative motion between the thermal particles and the accelerating observer, so I guess it would make sense. I vaguely recall it being refered to as a thermal shower.

    Regardless, yes you have to provide the energy to create those particles somehow. You're ending up with something other than the vacuum state and energy must be conserved.

  • Collecting Unruh effect particles

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  • Hawking gave that very explanation in his paper, so it's his own fault for inflicting bad science communication on the world haha

  • Collecting Unruh effect particles

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  • An asteroid falling into a black hole is in free fall, it's not accelerating.

    There are lots of related questions about black holes and hawking radiation one can ask and the answer is we don't know, we don't have the physics to describe it yet.

  • Collecting Unruh effect particles

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  • It doesn't, it's a direct result of mixing relativity and quantum physics. It's painfully complicated and I wouldn't even know where to begin because I only really know how to understand it through the abstract mathematics.

    I guess the simplest explanation I can give is that in quantum field theory, the definition of what is and isn't a particle depends on your frame of reference. Hence accelerating observers (in free space or hovering near black holes for example) see particles where others may see none.

  • Collecting Unruh effect particles

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  • FWIW that description of Hawking radiation is wrong and I think Hawking even says as much in his original paper on it. The real process is far far more complicated and involves tracing quantum field waves of various frequencies from the infinite past, through a collapsing star/black hole and into the future. Everything else is spot on.

    In QFT the definition of a particle itself becomes kinda abstract and hard to define in a consistent way.

  • Collecting Unruh effect particles

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  • I studied stuff like this in excessive detail a few years back but I don't remember it super well now. Here's my best guess from what remains of my intuition:

    An accelerating observer sees a shower of thermal particles due to a change in their reference frame. In QFT this is represented by a Bogoliubov transformation of the vacuum state to a non-vacuum state. I don't think the observer has done work on the vacuum at this point as it's technically still equivalent to the vacuum. When they collect particles, they put them onboard their ship in some container. When returning to an inertial frame they do work on them, expending energy and disrupting the vacuum state.

    In essence, when returning to the inertial frame, the state of the field is not represented by the inverse Bogoliubov transformation from the thermal Unruh state. There's a complicating factor where energy is injected into the vacuum, and what that looks like mathematically depends on your experimental setup.

  • Australia’s latest metro is about to open. Here’s how we’ll know if it’s working

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  • The comparison with the Sydney Metro is silly, they're extremely different projects. Melbourne's metro tunnel isn't a metro, it's a badly named but very welcome change to make some suburban lines through running.

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    Sasha [They/Them] @lemmy.blahaj.zone

    HRT and Mental Health

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    Mega Gruleotine

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    Arrested for disobeying rule

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    Eupho Rule

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    Mandorule

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    Lyrics Rule

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    Invasion Day Rule

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    Adrianne Lenker Rule

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    Too many pickles rule