Sasha
@Sasha@lemmy.blahaj.zone
Yes, that Sasha
- Comment on Het Pijnstillersparadijs: Europese Zelfbeheersing vs. Amerikaanse Pillenfeest 1 week ago:
- Comment on your mom falls significantly faster than g 2 weeks ago:
I’ve only ever done QFT in curved spacetime, but I don’t see any reason why you couldn’t do EM, it’ll be a vaguely similar process. I never actually dealt with any scenarios where the curvature was that extreme, and QFT in a curved background is kinda bizarre and doesn’t always require one to consider the specific trajectories, though you definitely can especially if you’re doing some quantum teleportation stuff. In my area it’s simpler to ignore QED and to just consider a massless scalar field, this gives you plenty of information about what photons do without worrying about polarisations and electrons.
It’s been a long time since I did any reading on the geometric optics approximation (in the context of GR this is the formal name for light travelling on null geodesics), but for the most part it’s not something you have to consider, even outside of black holes the curvature tends to be pretty tame (that’s why you can comfortably fall into one in sci-fi), so unfortunately I don’t know of any phenomena (in GR) where it’s important. QFT in curved spacetime generally requires you to stay away from large curvatures, otherwise you start entering into the territory of quantum gravity for which there is no accepted theory.
Outside of GR, it breaks down quite regularly, including I believe, for the classic double slit experiment.
- Comment on your mom falls significantly faster than g 2 weeks ago:
On that first point, calculating spacetime metrics is such a horrible task most of the time that I avoided it at all costs. When I was working with novel spacetimes I was literally just writing down metrics and calculating certain features of the mass distribution from that.
For example I wrote down this way to have a solid disk of rotating spacetime by modifying the Alcubierre warp drive metric, and you can then calculate the mass distribution along the radius. I did that calculation to show that such a spacetime requires negative mass to exist.
- Comment on your mom falls significantly faster than g 2 weeks ago:
Yeah, once you add in a second mass to a Schwarzschild spacetime you’ll have a new spacetime that can’t be written as a “sum” of two Schwarzschild spacetimes, depending on the specifics there could be ways to simplify it but I doubt by much.
If GR was linear, then yeah the sum of two solutions would be another solution just like it is in electromagnetism.
I’m actually not 100% certain how you’d treat a shell, but I don’t think it’ll necessarily follow the same geodesic as a point like test particle. You’ll have tidal forces to deal with and my intuition tells me that will give a different result, though it could be a negligible difference depending on the scenario.
Most of my work in just GR was looking at null geodesics so I don’t really have the experience to answer that question conclusively. All that said, from what I recall it’s at least a fair approximation when the gravitational field is approximately uniform, like at some large distance from a star. The corrections to the precession of Mercury’s orbit were calculated with Mercury treated as a point like particle iirc.
- Comment on your mom falls significantly faster than g 2 weeks ago:
Yeah it would fair point, I’ll be honest I haven’t touched Newtonian gravity in a long time now so is forgotten that was a thing.
There’s a similar phenomenon in general relativity, but it doesn’t apply when you’ve got multiple sources because it’s non-linear.
- Comment on your mom falls significantly faster than g 2 weeks ago:
Possibly?
A bowling ball is more dense than a feather (I assume) and that’s probably going to matter more than just the size. Things get messy when you start considering the actual mass distributions, and honestly the easiest way to do any calculations like that is to just break each object up into tiny point like masses that are all rigidly connected, and then calculate all the forces between all of those points on a computer.
I full expect it just won’t matter as much as the difference in massed.
- Comment on your mom falls significantly faster than g 2 weeks ago:
I actually thought the answer might be never, but a quick back of the envelope calculation suggests you can do this by dropping a ~1kg bowling ball from a height of 10^-11m.
This is an extremely rough calculation, I’m basically just looking at how big a bunch of numbers are and pushing all that through some approximate formulae. I could easily be off by a few orders of magnitude and frankly I didn’t take care to check I was even doing any of it correctly.
10^-11m seems wrong, and frankly it probably is. But that’s still 1,000,000,000,000,000,000,000,000 times further than the earth moves in this situation.
- Comment on your mom falls significantly faster than g 2 weeks ago:
This is not correct, the force on the objects is the same sure, but the accelerations aren’t so you can’t calculate them both in one go like this.
- Comment on your mom falls significantly faster than g 2 weeks ago:
If anyone’s wondering, I used to be a physicist and gravity was essentially my area of study, OP is right assuming an ideal system, and some of the counter arguments I’ve seen here are bizarre.
If this wasn’t true, then gravity would be a constant acceleration all the time and everything would take the same amount of time to fall towards everything else (assuming constant starting distance).
You can introduce all the technicalities you want about how negligible the difference is between a bowling ball and a feather, and while you’d be right (well actually still wrong, this is an idealised case after all, you can still do the calculation and prove it to be true) you’d be missing the more interesting fact that OP has decided to share with you.
If you do the maths correctly, you should get a=G(m+M)/r^2 for the acceleration between the two, if m is the mass of the bowling ball or feather, you can see why increasing it would result in a larger acceleration. From there it’s just a little integration to get the flight time. For the argument where the effect of the bowling ball feather is negligible, that’s apparent by making the approximation m+M≈M, but it is in this system an approximation.
I could probably go ahead and work out what the corrections are under GR but I don’t want to and they’d be pretty damn tiny.
- Comment on Scientists dismayed as UK ministers clear way for gene editing of crops - but not animals 2 weeks ago:
Depending on the way it’s modified, I think there’s some environmental risk particularly for soil erosion and potentially cross breeding with non-modified crops.
I don’t think these should stop us from making better food sources, but it does concern me because there isn’t much corporate incentive to adequately test for these things.
- Comment on Police use capsicum spray on neo-Nazis after clash at Melbourne asylum seeker rally 4 weeks ago:
Of course, before any of this they first sprayed one of the speakers for the asylum seeker rally…
Pretty damn typical of cops to not arrest the nazis or do anything useful for the community, they need to get to other rallies so they can pepper spray children and trample trans youth with their horses.
- Comment on CODA 5 weeks ago:
This looks like a score for a Tim Minchin show lol
- Comment on Horrors We've Unleashed 5 weeks ago:
Didn’t seem to doesn’t necessarily mean it didn’t happen, it can be difficult to quantify. Most people don’t notice a lot of the constant large scale ecological devastation that does happen.
The real concern is that even if it was fine in one location, that can’t reliably be assumed to be the case for other ecosystems. This issue is really complicated, we’ve acted hastily in the past and done some insane lasting damage so I’d say it’s best to be careful.
All that said, even if I’m vegan and this whole thing makes me extremely uncomfortable, working to eradicate malaria is objectively good.
- Comment on [NSW Premier] Chris Minns faces backlash from Labor MPs over ‘incredibly dangerous’ push to ban costly protests 1 month ago:
Then stop sending thugs to assault peaceful protestors, problem fucking solved.
- Comment on Outliers 1 month ago:
- Comment on International Woof 1 month ago:
Sprich Deutsch du Hurensohn
- Comment on Why is space 2 dimensional? 1 month ago:
Best video you’ll ever see on the topic imo (and very short)
- Comment on SGVsbG8sIFdvcmxkIQ0K :) 1 month ago:
Why does this kinda look like Doug Walker?
- Comment on Large crowd of protesters gather at Land Forces defence expo in Melbourne's CBD 2 months ago:
I’ve had friends in hospital today because of the fucking pigs. Every damn time, they’re defending the worst people on earth and assaulting the best
- Comment on Thank you! 2 months ago:
Coffee is just a bean soup
- Comment on Seconds 2 months ago:
Oh god, no fluid mechanics is way too difficult. I stuck to studying quantum effects of black holes, which is much easier.
- Comment on Seconds 2 months ago:
Constance? Never heard of her
- Comment on Watching ml and world argue in every thread be like. 2 months ago:
Having never done it as part of one such group, I don’t know exactly what goes on, but essentially there’s a large body of literature on leftist political concepts, covering the ideas of why anarchy rather than archy, how to practice it, how to organise etc. I’m definitely the wrong person to explain it, generally socialists (at least here) are the ones doing all the reading, I’m a lot more interested in praxis tbh.
Some classic anarchist writers include Kropotkin, Bakunin and Proudhon. But the communist and socialist literature often applies too.
The anarchist library has lots to browse and the anarchist faq is a great starting place despite its huge volume of content, I highly recommend casually browsing it.
- Comment on Seconds 2 months ago:
As a theoretical physicist, units are for chumps
- Comment on Watching ml and world argue in every thread be like. 2 months ago:
We do! In my area there are quite a few of us and we operate a number of collectives providing things like: Free meals Free groceries Bike repair workshops Theory reading groups Clothing Social activities
Of course there’s a lot of direct action going on for various causes.
- Comment on Labor branch in Albanese’s electorate passes motion supporting Fatima Payman 4 months ago:
This whole debacle is, to me, more proof that you can’t change a system from the inside, all you can do is support and legitamize it.
Good on Payman for taking a stand, hopefully this leads to either actual change in the party or to people realising that Labor really isn’t any less corrupt than the LNP.
- Comment on Protestors vow to keep disrupting train lines leading to world's largest coal port 4 months ago:
Fucking heros, keep it up ✊
- Comment on How to know you'll turn out trans? 4 months ago:
Yeah, fair enough. Best of luck, you deserve happiness and I’m rooting for you
- Comment on How to know you'll turn out trans? 4 months ago:
I’m so sorry that you had such a horrible journey, but I’m so proud of you for making it this far
- Comment on [Labor senator] Fatima Payman says she's been 'exiled' and is 'reflecting on future' within Labor 4 months ago:
Yeah, the Labor party has a rule that you have to vote with the party. It’s insane and she’s the one person willing to standup to their genocidal policy