• Physics Discussion
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Huzzah! My first ever paper (first author for what it's worth) was accepted for publication with only a single change requested: the inclusion of three more references. I'll count that as a win. I've done it. I've contributed to the body of knowledge of science. I've contributed to physics. The quantity and quality of my contribution may be debateable but it's non-zero and I'm feeling pretty happy about that.
[QUOTE=sltungle;52351660]Huzzah! My first ever paper (first author for what it's worth) was accepted for publication with only a single change requested: the inclusion of three more references. I'll count that as a win. I've done it. I've contributed to the body of knowledge of science. I've contributed to physics. The quantity and quality of my contribution may be debateable but it's non-zero and I'm feeling pretty happy about that.[/QUOTE] Abstract? If you're allowed to share it before publishing that is.
[QUOTE=download;52351682]Abstract? If you're allowed to share it before publishing that is.[/QUOTE] [URL="https://arxiv.org/abs/1612.06870"]It's been on the arXiv for some time.[/URL] It's probably nothing terribly exciting to most people, but we're trying to lay some more or less unshakeable foundations for some future stuff that people might be quick to dismiss as crazy if they don't see how the basics come together to make things work (or conspire to make things seem like they work, rather). In many regards, this is essentially the same work that Lorentz and Poincaré did some hundred years ago now in trying to build a consistent theory of the aether. The reason we're doing this is because we're trying to see how far analogue gravity models (or more broadly, analogue relativity models) can be pushed before they break down (or... if it turns out that they don't break down, then what the hell)? We're trying to show how, in the first instance, you can consider some class of observers to see a universe that they'd describe as relativistic in a physical system that actually has a preferred reference frame (like the aether of old). If you read any of it, hopefully it does a good enough job of explaining itself. I can try to answer any questions that you may have if you're interested.
That's super cool! Would there be an application of this phenomenon? I know they use pools with vortices to also investigate the curvature of space and stuff like that.
Nice diagrams. I'll probably read it maybe tomorrow when I've got more time. Looks like the requirements are pretty minimal from the equations
[QUOTE=JohnnyMo1;52352825]Nice diagrams. I'll probably read it maybe tomorrow when I've got more time. Looks like the requirements are pretty minimal from the equations[/QUOTE] Oh yeah, super straight forward stuff. Just laying down the ground work to show that it's not an insane man's endeavour in trying to push analogue gravity models forward. A lot of people apparently talk about how they're only relativistic in 'one direction' and so that ultimately in the long run they won't be able to reproduce this or that feature of GR, but with the correct operational definitions it appears to internal observers as though SR is valid in both directions so there might be hope yet in learning from analogue gravity models. [editline]14th June 2017[/editline] Also, "nice diagrams," makes the fucking days and days that I spent painstakingly writing modular tikz code to make those diagrams for arbitrary scenarios worth it. Thank you!
i've been thinking a lot about gravity recently. it's described as a force, but when looking into it it seems to just be a convenient term to describe mass attracting mass, rather than a tangible force. and part of this is i cant understand how black holes can pull with enough force to prevent light from escaping, is it's mass not the same as it was before it became a black hole? why does the escape velocity become so high? [editline]16th December 2017[/editline] also i don't know shit about physics, are there some good books i can get to get me started?
A Brief History of Time: From the Big Bang to Black Holes by Stephen Hawking A Briefer History of Time by Stephen Hawking and Leonard Mlodinow Relativity: The Special and the General Theory by Albert Einstein (Hard to find a "proper" copy but most common ones are decent I suppose) to name a few. [editline]16th December 2017[/editline] I assume you are not talking about textbooks.
[QUOTE=Pat.Lithium;52981502]i've been thinking a lot about gravity recently. it's described as a force, but when looking into it it seems to just be a convenient term to describe mass attracting mass, rather than a tangible force.[/QUOTE] Sort of. The reason it gets said that gravity is "not a force" is because of the equivalence principle: if you're on a (sufficiently small) rocket with no windows with the engines off, you can't do an experiment that will let you know if you're free falling toward a planet or in deep space, far from the effect of any gravitating body. So free falling should really be thought of as "unaccelerated" motion, rather than something like standing on the surface of a planet, which you can measure. Gravity possesses this sort of universality because your gravitational mass and inertial mass are the same, i.e. the "charge" that determines how strongly you interact with gravity is the same thing that determines how hard it is to accelerate you. Other forces don't have that going on. [QUOTE=Pat.Lithium;52981502]and part of this is i cant understand how black holes can pull with enough force to prevent light from escaping, is it's mass not the same as it was before it became a black hole? why does the escape velocity become so high?[/QUOTE] The escape velocity is the same at the same radius. For instance, if Earth was compressed into a black hole, the escape velocity at Earth's old radius would still be about 11 km/s. The difference is you can now the surface of Earth is gone, so you can get much closer to the center of mass, and all the mass is concentrated about it. So at the smaller radii you can now access, the escape velocity is much stronger. Note that thinking about "escape velocity" is really only a Newtonian approximation to begin with. It fails as you get into the regime of very strong gravitational fields. Earth's radius away from an Earth-mass black hole is many, many Schwarzschild radii away though, so it holds up fine there. But the fact that light can't escape is less about "escape velocity" and more about the fact that all paths are curved so strongly inside the event horizon that there are no more lightlike paths connected to "far away" from the black hole. The fact that a Newtonian calculation for a Schwarzschild black hole at the event horizon gives an escape velocity of c is really just a confusing accident.
i'm going to take my first college physics and a college calculus class next semester, and i'm really excited for my physics class. i've loved physics since last year after i realized just how cool equations really are. to me, it's [I]fucking amazing[/I] how you can make an equation from observations in the real world and have it be essentially universal in terms of what it is capable of describing. for example, a simple observation can lend you the fundamental newtonian equation f=ma. from just this, you can describe the interaction between a force and [I]virtually any object anywhere[/I]. the fact that an equation like that is so universal and constant and telling is what is so captivating of physics.
[QUOTE=Trixil;52986090]i'm going to take my first college physics and a college calculus class next semester, and i'm really excited for my physics class. i've loved physics since last year after i realized just how cool equations really are. to me, it's [I]fucking amazing[/I] how you can make an equation from observations in the real world and have it be essentially universal in terms of what it is capable of describing. for example, a simple observation can lend you the fundamental newtonian equation f=ma. from just this, you can describe the interaction between a force and [I]virtually any object anywhere[/I]. the fact that an equation like that is so universal and constant and telling is what is so captivating of physics.[/QUOTE] Just wait till u get on that quantum train tho uh oh Me after seeing classical mechanics break down at the quantum level: Wut duhhh O_o
Spent 2 hours today trying to figure out why a term in a field theory calculation was off by a constant factor only to realize that I was using the wrong metric convention. And that is why the field theorists' metric convention sucks. Long live -+++
[QUOTE=Trixil;52986090]i'm going to take my first college physics and a college calculus class next semester, and i'm really excited for my physics class. i've loved physics since last year after i realized just how cool equations really are. to me, it's [I]fucking amazing[/I] how you can make an equation from observations in the real world and have it be essentially universal in terms of what it is capable of describing. for example, a simple observation can lend you the fundamental newtonian equation f=ma. from just this, you can describe the interaction between a force and [I]virtually any object anywhere[/I]. the fact that an equation like that is so universal and constant and telling is what is so captivating of physics.[/QUOTE] Oh boy, have fun! For me the biggest change when moving up to college-level stuff was how rigorous and airtight everything seemed, at least compared to high school. The curriculum removed many shortcuts and simplifications present in phys at the HS level and basically slapped us and said "fuck you time to go, but we're still gonna leave all these other simplifications in because the math required is a few years out for y'all if not more haha have fun!" It really gave me a feeling for how complicated physics must potentially become. I knew that I was playing in a sandbox while in high school, but the size and necessity of the sandbox didn't really strike me until physics 2 (electricity and magnetism in my school). Of course, depending on the university, the level of rigor and difficulty can vary immensely. But geeeez, my school, aaaaaaa. I hadn't planned on majoring in physics regardless but that class made me bow my head anyways. Don't get me wrong, it's immensely satisfying to learn so much about... well, how the universe fundamentally works, and then the joy and wonder that comes when you realize that there's still so much more to learn and describe in intense detail is the cherry on top.
[QUOTE=Repulsion;53008179]Oh boy, have fun! For me the biggest change when moving up to college-level stuff was how rigorous and airtight everything seemed,[/QUOTE] Am learning about path integrals. Cannot confirm rigor. "And here we integrate infinitely many times..."
I have an uneducated question for you guys regarding orbital mechanics and such. In Kerbal Space Program, calculating DeltaV involves having to use the gravitational acceleration value g, which is approximated to 9.81 m/s^2 in the game. After doing a bit of light documentation on gravitational acceleration on [url=https://en.wikipedia.org/wiki/Gravitational_acceleration]this wikipedia page[/url], I found the below formula: [img]https://wikimedia.org/api/rest_v1/media/math/render/svg/730c340053be238bcc55fbb54827149606377c6d[/img] where M is the mass of the attracting object, r-hat is the unit vector from center-of-mass of the attracting object to the center-of-mass of the object being accelerated, r is the distance between the two objects, and G is the gravitational constant. Given that r can change at any point, it will have an inverse-square "effect" on g. See the below DeltaV formula taken from the KSP wiki: [img]https://wiki.kerbalspaceprogram.com/images/math/6/9/9/699abff01f7e7d587ecbf434866c8a75.png[/img] where g is the value of 9.81 m/s^2. Wouldn't the value of g have to be adjusted depending on how far the craft is located from the body being orbited? As far as I can tell, the further away the craft is from the body being orbited, the less DeltaV you get out of the craft, which doesn't seem to make much sense. Could someone explain this for me?
I'm seriously considering hosting a campaign to change the terms "it's not rocket science" and "it's not brain surgery" to "It's not optics engineering" Been reading through the book. "Solid State Laser Engineering" This stuff is confusing as hell. I'm trying to wade through it by myself. I think I need to go back to Uni.... Been playing with concepts for a 50W YAG laser.
[QUOTE=supervoltage;53074451]I have an uneducated question for you guys regarding orbital mechanics and such. In Kerbal Space Program, calculating DeltaV involves having to use the gravitational acceleration value g, which is approximated to 9.81 m/s^2 in the game. After doing a bit of light documentation on gravitational acceleration on [url=https://en.wikipedia.org/wiki/Gravitational_acceleration]this wikipedia page[/url], I found the below formula: [img]https://wikimedia.org/api/rest_v1/media/math/render/svg/730c340053be238bcc55fbb54827149606377c6d[/img] where M is the mass of the attracting object, r-hat is the unit vector from center-of-mass of the attracting object to the center-of-mass of the object being accelerated, r is the distance between the two objects, and G is the gravitational constant. Given that r can change at any point, it will have an inverse-square "effect" on g. See the below DeltaV formula taken from the KSP wiki: [img]https://wiki.kerbalspaceprogram.com/images/math/6/9/9/699abff01f7e7d587ecbf434866c8a75.png[/img] where g is the value of 9.81 m/s^2. Wouldn't the value of g have to be adjusted depending on how far the craft is located from the body being orbited? As far as I can tell, the further away the craft is from the body being orbited, the less DeltaV you get out of the craft, which doesn't seem to make much sense. Could someone explain this for me?[/QUOTE] It's because you're misunderstanding the purpose of 9.81 m.s^-2. Notice they give a figure rather than a variable meaning it's fixed. Your delta-v does not change because of the gravitational acceleration. The 9.81 m.s^-2 is there because of specific impulse (I_sp) part of the equation. It comes from converting weight (measured in newtons) to mass measured in kg. It would help you to look at the derivation of the delta-v formula. A lot of people prefer the other version of the formula because it's not geocentric: delta-v=v_e*ln(m_0/m_f) Where v_e is the effective exhaust velocity.
Science stuff
Joe Polchinski died of his glioblastoma on the 2nd. [url=https://arxiv.org/abs/1708.09093]Here's[/url] what is essentially his memoir that he wrote a few months back. I got the first volume of his string theory textbook this past Christmas. All the more reason to make time to work through it.
im SO excited for grad school hot damn
reduced mass central force problems are very annoying
Can anyone here tell me the application of Fermi gas? You know a gas full with fermion patricles at very low temperature (if not at zero).
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