|
Who are you? I am a graduate student, and I do theoretical astrophysics for a living. I feel an almost religious passion for physics and the cosmos, and it is my personal goal to share a little bit of that with you. What is the purpose of this thread? There is a thread in SAP called the Science/Physics Questions Megathread, which in tehory covers the subject of this one, but in practice mostly get used for homework questions and stuff. If you have a homework question, I suggest you go over there. This thread is about more general knowledge stuff; it's for things that you've always wondered about but could never understand the articles in Popular Science or whatever other lovely magazine or newspaper you read them in (protip: pretty much all science reporting is terrible, it's not your fault). Hopefully, also, by putting this in Ask/Tell instead of in SAP will get a broader audience, with less preaching to the choir. In explaining these things to you, I hope to excercise my ability to explain science. Tell me when I'm not being clear, when you don't understand what I'm saying, so that I can improve. How do I become scientifically literate / what is scientific literacy? Well, the way I became scientifically literate was a path that I can't trace very well because it started back when I was very young. My parents did a good job in raising me to be inquisitive and to always try and understand the world around me. They taught me math through educational videogames, and they taught me science through educational television. They made it interesting enough that by the time I enrolled in school I was ready to absorb and enjoy science (although unfortunately a lot of elementary school science is plain incorrect). It didn't even occur to me until my late teens that there even was such a thing as a scientifically illiterate person - someone who, through some thought process I didn't understand, doesn't care about how the world works, why things happen, and how to distinguish fact from fiction. If you want to become scientifically literate, there are plenty of places to start. I suggest that everyone who has the means (including every single American, since it's on Hulu) to watch Cosmos: A Personal Voyage, a thirteen-part documentary about, well, the cosmos, written and narrated by Carl Sagan. I vaguely remember watching Cosmos when I was about five or six, and I can't imagine I understood much of it, but I think that something about Sagan's wonder and enthusiasm for understanding the universe managed to imprint on me. Don't be put off by Sagan's lilting voice or the fact that he is the nerdiest hippie you've ever seen. To him, being a part of the cosmos was like being a kid on Christmas, and he is full of barely-restrained enthusiasm. Cosmos was released over thirty years ago, and yet there is very little that needs updating for more recent findings, and the core concepts are timeless. Other things that might be good for you: Anything by Carl Sagan. In particular, The Demon Haunted World: Science as a Candle in the Dark is quite good; it's about skepticism, in particular as it relates to UFOlogy. If you like science fiction about actually plausible situations, read Contact, which is about the search for extraterrestrial intelligence and what might happen if we managed to find one, while explaining plenty of real science along the way. Surely You're Joking, Mr. Feynman! is the fantastical autobiography of Richard Feynman, a Nobel-winning scientist who helped build the atom bomb, revolutionized particle physics, and helped unravel the mystery of the Challenger explosion. I strongly suspect many of the stories are greatly exagerrated, but he talks about many different aspects of physics, science in general, and scientists, in an entertaining manner. Mythbusters, though populated with special effects artists rather than scientists, is a great way to learn the most basic idea of all science: have an idea, test if it is true. They are not very scientific about how they test the myths, but that poo poo's better than motherfucking Shark Week. If you're young enough to still be in school, enroll in your high school/college's basic physics class(es), and hope the professor(s) doesn't suck. Pay attention and you might learn something cool. The music videos at symphonyofscience.org are pretty awesome, starting with the viral video "A Glorious Dawn" also known as auto-tuned Carl Sagan. You won't learn a lot of science from them, but they are a glimpse of the distilled awesome of the universe as interpreted by famous and eloquent scientists. Powers of Ten, an exploration into the vast distances of the cosmos and the minuscule sizes of subatomic particles. Everyone should watch this, it's a real mind-bender. You mention the word "cosmos" a lot, what is a "cosmos" anyway? In practical, modern English terms, it basically means "universe." Cosmos is a Greek word meaning "order." The concept of a cosmos is that there are rules, patterns, motifs, and equations that govern the working of the universe. It is the concept that the ancient Greeks gave the idea that since the sun rose yesterday and the day before, it will rise today - this fantastical, almost absurd notion that the things we experience are not random, nor governed by some whimsical intelligent being, but are the result of fundamental order in the universe. It's the drat convenient notion that we can use the past to predict the future. It is the core of science, the most important axiom. As Einstein once said, "The most incomprehensible thing about the world is that it is comprehensible." What kind of questions are you expecting to answer? Here are a few to get you started, if anyone's interested: What's the deal with that whole big bang thing? Black holes: what the christ? Could a lightsaber ever really exist? Why can't we go faster than the speed of light? Does Spider-Man having the proportional strength of a spider even make any sense? How are spiders and other bugs so drat strong, anyways? Why is astrology basically the worst thing ever? Aliens: what's the real deal? Why are we spending billions of dollars to make a giant underground circle that blows tiny stuff up under Switzerland and France? What is dark matter? Dark energy? Why is the cosmic microwave background so important (also, what is it)? What movie has the worst science? Best? I heard that all matter is made up of tiny vibrating strings. What??? What's a quantum? Why do people living on mountains need some combination of salt, pressure-cookers, and/or extra time to cook a potato? Is time travel possible? How, or why not? Double rainbow all the way across the sky - what does it mean? What's a supernova? How do we know so much about the stars and poo poo when they are so far away? What shape is the universe? Are you an atheist or what, and why? What's a cosmic ray? What is antimatter? Why does my shower curtain tend to creep up and stick to my leg? How does an atom bomb work? How does a mirror know which way is left-right, and switch it, while leaving up-down unaffected? How does a lens focus light? What's a tachyon, and why does Data always prattle on about them on Star Trek? How does a distillery work? Water, fire, air and dirt; loving magnets - how do they work? Where else can I find answers to my questions? For many of them, there are key words that are easy enough to google and come up with some good results. Certainly basic things like magnets and rainbows can be found in easy-to-understand Wikipedia articles and similar things. Googling certain other things, like string theory, is a good way to read tons of terribly written material that will give you bad ideas unless you understand the physics in detail already. I imagine that for the layman it can be hard to distinguish between these two things, but if you're still confused after googling around, I will be here to set you straight. Still other topics will only get you fiction and speculation, things like time travel. Still more questions are just hard to google for - such as, to take an example from the list I just wrote, "how do we know so much about stars when all we can do is look at them from far away?" In any case, if you don't want to bother me, you can try some google-fu and see what you come up with, and hopefully it won't be too terrible. Can I help you answer questions? That depends - what is the question, and do you have a physics degree? Certainly on basic things like mirrors and rainbows and atom bombs and electricity, you're probably fine, as long as you're confident in what you're talking about. But no one understands quantum mechanics nor relativity until (maybe even after) they've done the formal mathematics. So if you learned about string theory or whatever from popular science, you're not qualified to explain it to other non-physicists. It's just an unfortunate fact that the cosmos isn't as orderly as we might like and our everyday intuition leads us into dangerous traps when it comes to all things quantum and/or relativistic, and it's all to easy to misrepresent our own flawed intuition as fact when speaking to other laymen. That's enough for now. I can't be always watching this thread, and I fear it might suck up too much of my time (grad students are proverbially pretty busy), but I'll give it a try and answer questions in batches at least once most days if this thread gets flooded enough to warrant it (but no promises). Or else I may just answer questions randomly throughout a bored workday. I don't know. We'll see how it goes. I'm constantly excited to spread my love of physics to other people, and I hope you are as excited to learn about it. DontMockMySmock fucked around with this message at Sep 23, 2010 around 07:50 |
| # ? Sep 20, 2010 10:10 |
|
|
|
| # ? May 20, 2013 02:06 |
|
|
Answer all of your expected questions  or start with this oneWhat movie has the worst science? Best?
|
| # ? Sep 20, 2010 14:08 |
|
|
DontMockMySmock posted:What movie has the worst science? Best? What's your favourite science fiction? Did you watch/enjoy the movie Moon? Any criticisms if you did see it? (I remember thinking it seemed pretty rigorous scientifically, except maybe the very end...) Somewhere between reading Neuromancer and watching Ghost in the Shell I decided to become an EE major, but that sort of sci-fi doesn't seem to break physics much. Or does it?
|
| # ? Sep 20, 2010 14:22 |
|
|
I did terribly with high school physics where we were calculating all the forces acting on objects at any given time. However, I did great with everything but that. I'm great with math, at least up through calc 3. If I wanted to self-teach myself that particular area of earth-bound gravity influenced physics, what the hell is it called and what books are good at unfucking that?
|
| # ? Sep 20, 2010 14:25 |
|
|
Is there a consensus on whether space-time is discrete or continuous? Can you explain how Planck units works and what their significance is?
|
| # ? Sep 20, 2010 15:04 |
|
|
Regarding the fate of the sun, how does the planetary nebula form? Does the sun just literally fall apart?
|
| # ? Sep 20, 2010 15:44 |
|
|
Panzer Pirate posted:Somewhere between reading Neuromancer and watching Ghost in the Shell I decided to become an EE major, but that sort of sci-fi doesn't seem to break physics much. Or does it? From what I understand, nanotechnology is something that shows up in sci-fi that actually has a good chance of developing a lot more. There's also no scientific reason for AI to be impossible, though it'll probably take an extremely long time to develop. Question: Exactly what sort of math courses do you take as someone in astrophysics? How does your math coursework compare with an actual math major/math grad student? I'm sure you have to take stuff like linear algebra, calc III, and differential equations, but what else? What do people in physics generally think of people in biology (and other natural sciences)? Also, what's the general "culture" like, and if you know, how is it different? I work in biology (bioinformatics more accurately), and there seems to be a big spread between people without much math background (some of the post-docs here) and people who are really skilled programmers and write genome mapping algorithms. My personal belief is that it wasn't until the past couple decades that those skills became very pertinent, and that the shift is still in progress.
|
| # ? Sep 20, 2010 16:04 |
|
|
Where do you go to school? What program? What do you want to do with your degree? Are you more of a Treasure Mountain! or a Math Blaster kind of guy? Edited out the pointless flaming. Gomegoth fucked around with this message at Sep 20, 2010 around 16:43 |
|
| # ? Sep 20, 2010 16:18 |
|
|
If a person travelling at C 'fired' a torch in front of them would the light from the torch surround them or be in front of them perpetually?
|
| # ? Sep 20, 2010 16:23 |
|
|
Do you know any good resources for students in introductory physics? How can I become as excited about physics as you?
|
| # ? Sep 20, 2010 16:29 |
|
|
How good are you at arxiv vs snarxiv?
|
| # ? Sep 20, 2010 16:53 |
|
|
Where would you like to work after you finish graduate school? Also, are you an atheist? If so, have you ever been religious? Do you think religion and science can be reconciled or do you find them to be two separate entities?
|
| # ? Sep 20, 2010 17:15 |
|
|
Aluminum Record posted:What movie has the worst science? Best? The worst science is easy enough to answer: The Core. An earthquake-superweapon being developed by the US Military causes the Earth's core to stop spinning (impossible) which causes all kinds of trouble when our magnetic field vanishes. So a team of bad actors get in a ship made of metal that turns heat into electricity (impossible) and drill down to the center of the earth (impossible) in order to kick-start the rotation of the earth (impossible) using nuclear weapons (especially impossible). Other impossible things happen along the way. It's quite an entertaining movie. The best I gave away somewhere in the OP, which is the movie based on Car Sagan's Contact. It makes a few gaffes in the name of making the movie more dramatic but overall it's good. It portrays the science of radio astronomy mostly accurately, and nothing physically impossible happens until the climax, where (naturally) speculative physics becomes involved (because it is science fiction, after all). But the speculation is well founded in our current understanding of physics. Panzer Pirate posted:What's your favourite science fiction? Did you watch/enjoy the movie Moon? Any criticisms if you did see it? (I remember thinking it seemed pretty rigorous scientifically, except maybe the very end...) My favorite science fiction authors are Robert Heinlein, Phillip K. Dick, and Spider Robinson. None of them are particularly good at writing good science, but they're good at writing good characters and engaging stories. Moon was a good movie. There wasn't anything especially wrong with the science in it, except for the clone copying thing, and the fact that no moon base could ever run with only one person. I'm actually in the middle of reading Neuromancer right now. Mostly the parts of Neuromancer that are questionable scientifically are biology things, so I'm not too qualified to comment. Although there is one character who projects psychic images or something like that? That's pretty bad, physics-wise. I haven't read Ghost in the Shell so I don't know about that. Not an Anthem posted:I did terribly with high school physics where we were calculating all the forces acting on objects at any given time. However, I did great with everything but that. I'm great with math, at least up through calc 3. If I wanted to self-teach myself that particular area of earth-bound gravity influenced physics, what the hell is it called and what books are good at unfucking that? If you want a rigorous mathematical treatment (and it sounds like you do), any third year mechanics textbook can teach you. The book I learned it from was by Thornton and Marion. You can also probably find a lot of stuff about it on the internet; search for "Newtonian gravity" and "Kepler's laws" and you can probably come up with some good stuff. Bodhi Tea posted:Is there a consensus on whether space-time is discrete or continuous? There is no consensus. Space-time is a nasty beast, and the only working theory we have has a continuous picture. But somewhere in the realm of quantum mechanics there is a different story - we just don't have any idea what it is, yet. The most popular theories about it are string theory and loop quantum gravity, if you're interested in reading up on them, but since they are some of the crazier bits on the cutting edge of physics, you're likely to get a lot of articles written by people who are more enthusiastic about it than is warranted. Planck units are basically a set of units that make certain constants of nature equal to 1. The constants it sets to 1 are the speed of light in a vacuum c, Newton's gravitational constant G, the reduced Planck constant h-bar, the Coulomb force constant 1/(4 pi epsilon-naught), and Boltzmann's constant k. So c is equal to one Planck length per Planck time. And so on. The only place where Planck units are ever used is when dealing with quantum gravity, since G only comes up in gravity and h-bar only comes up in quantum mechanics. In fields other than quantum gravity, different sets of units are used that set only some of the constants to 1. comaerror posted:Regarding the fate of the sun, how does the planetary nebula form? Does the sun just literally fall apart? When a star runs out of hydrogen fuel in its core, the core collapses under gravity and the envelope expands as the core heats up. The envelope is mostly held up by radiation pressure, i.e. the charged particles in the envelope are bombarded by enough light such that the light holds them up against gravity. As more and more fuels are exhausted in the core, the core heats up more and more, and (in stars the size of our sun) the radiation pressure eventually just blows the envelope away in an expanding cloud of gas. What's left then is a "white dwarf" consisting of mostly carbon and oxygen and an expanding shell of gas that will eventually become mixed in with the rest of the gas and dust in the surrounding area. With stars larger than the sun, the story gets more exciting, but that's a story for another time. Ytlaya posted:Question: Exactly what sort of math courses do you take as someone in astrophysics? How does your math coursework compare with an actual math major/math grad student? Physicists take all the classes you mention, but also need to know infinite series, partial differential equations, Fourier analysis, and complex analysis. At the end of the first two years of math in a physics degree, you've basically got the first two years of a math degree, but at that point their paths diverge. Contrary to popular opinion, physicists don't look down on biologists or anything like that. I have a lot of friends in biology, in fact. I guess my answer to your question is that people in physics don't think much about biologists at all. The "culture" is much like the culture anywhere in academia, except that all of the jokes you see on The Big Bang Theory are ones we've heard jillions of times already. Gomegoth posted:Where do you go to school? What program? What do you want to do with your degree? Are you more of a Treasure Mountain! or a Math Blaster kind of guy? Aww, but the pointless flaming was alright! My answer to your now-deleted pointless flaming is that YOU may already know what "cosmos" means, but I've met people who don't know the difference between "cosmology" and "cosmetology," so I thought it would be good to make that particular point very clear. It's a word that doesn't get used much. I like it better than "universe," personally. Man, I played both Treasure Mountain and Math Blaster when I was little. I have fond memories of both, but especially Treasure Mountain because there was a whole series of games by the same company - Mathstorm Mountain, Gizmos and Gadgets. . . As for my career aspirations, I hope to be able to continue doing research, somewhere in a tenure-track professorship. I like teaching, too, so a university professorship is likely in my future. ibroxmassive posted:If a person travelling at C 'fired' a torch in front of them would the light from the torch surround them or be in front of them perpetually? There's no real way to answer this question because a person traveling at c doesn't make mathematical sense within the framework of special relativity. But I can tell you about a person traveling at very nearly c: an observer standing on the ground would say that the light from his flashlight would be traveling just faster than he is, at c relative to the ground. And the traveling guy would see the light speed in front of him at c relative to himself. This sounds like a contradiction if you're used to ordinary situations at slow speeds, but in fact it's an expression of the founding principle of special relativity - the speed of light in a vacuum is always c, relative to any observer. The contradiction disappears when you consider that these two observers have different points of view of space and time. Alhara posted:Do you know any good resources for students in introductory physics? How can I become as excited about physics as you? When I was first learning physics in high school, we watched a series called The Mechanical Universe, with a Caltech professor lecturing and a voiceover artist that reminded me of Sigourney Weaver. They managed to be pretty entertaining and pretty informative about every subject you might come across in first-year physics. I think you can find them on Google Video. For reading material, besides your textbook, there's Feynman's Lectures in Physics, which is always praised, but I haven't read it because I never knew it existed until I had already passed that level. As for becoming excited about physics, well, it's something that just happened, I don't think you can really force it. Reading popular science can certainly help, if you avoid the lovely stuff (unfortunately you have to already know a lot about physics to know what's lovely). A Brief History of Time and Cosmos come to mind immediately (especially Cosmos, go watch Cosmos dammit!). manifold posted:How good are you at arxiv vs snarxiv? Ms. Happiness posted:Where would you like to work after you finish graduate school? Any of the good universities for astrophysics would be good - Caltech, MIT, and Cornell are the first ones that come to mind. If I don't cut the mustard for those, any decent physics department will do. Before I say whether I'm an atheist, I ought to define the term, since there are two different definitions. Some people think of "atheist" as someone who believes there isn't a god, or thinks they know that there isn't a god. Well, what is a "god" anyway, and how can I prove there isn't one? That's an unreasonable definition. I'm an atheist in that I think that it's fantastically unlikely that any religion I've ever heard of has any idea what they're talking about. One scientist once put it like this: if the word "atheist" is too extreme, instead call me a "teapot agnostic." There could be a teapot orbiting Saturn, and you can't prove it exists nor can I disprove it, but it strikes me as unlikely. I was raised Christian, but as I got older the stories seemed more fantastical and ridiculous until somewhere around when I was thirteen or fourteen I just stopped believing in anything. As a testament to the power of religion, I then got pretty depressed for a while (this also coincided with a major historical event that we may have just been commemorating an anniversary of, and there's nothing like a major terrorist attack to shatter any last vestiges of a belief in God). Then I started learning physics, and things started looking up. I have religion, now, but my religion is a devotion to the cosmos. Einstein famously believed in God as immortalized in his famous quote "He does not play dice." But his God was certainly not a personal god like the Christan or Jewish god. His God was simply the cosmos, in all its beauty, splendor, logic, and order. That's my God too. It doesn't seem to have anything to do with what the word God usually stands for, but the similarity lies in that the emotion felt by religious people, "rapture" you might call it, is the same emotion that I feel when we think about the universe. A deep reverence for this entity greater than yourself. Einstein once called it the "cosmic religious feeling." Not to compare myself to Einstein, he's just the most famous example of a physicist who believed in this same "God." And to the final question - can religion and science be reconciled? Well, I'm not sure it's even a valid question. Religion's primary function is to tell you how to live your life, what your moral values should be, and so on. Science has no answer to these questions (yet? Sociology has a long way to go). As long as people don't hang on to the idea that this book, haphazardly handed down for thousands of years after being written by an old hermit, has the unadulterated truth in it, there's no real conflict. The messages of religion or usually things like "do unto others as you would have them do unto you," and science surely doesn't have a problem to that. The only reason the conflict exists is because some people choose to believe that the testimony of that thousands-of-years-old hermit passed through the longest game of "telephone" ever is more reliable than their own eyes when it comes to simple things like "how old is the earth." In fact, I would go so far as to say that the world would be a better place if everyone just listened to Jesus for a change (especially those people who claim to worship him).
|
| # ? Sep 20, 2010 17:54 |
|
|
What field of theoretical astrophysics do you work in? I'm a graduate student as well (a baby grad student about to take the quals, yikes!), but I do observations and mostly work on the high redshift universe/galaxy evolution right now.
|
| # ? Sep 20, 2010 18:25 |
|
|
Did we ever figure out how elements heavier than iron can form in supernovas? I read a book that was talking about this being a problem... but I never finished it. Also... on cosmic background radiation, is there any theory that this could be anything but the heat left over from the big bang or does it pretty much seal the deal about the big bang?
|
| # ? Sep 20, 2010 18:30 |
|
|
What's your take on the whole mathematics person/physics person rivalry? (I say this as someone with many friends studying/researching physics.) Edit: Also, as someone working in theoretical physics, how does your day-to-day research differ from that of a mathematician?
|
| # ? Sep 20, 2010 18:30 |
|
|
Relativity says space(-time) is curved. How can nothing be curved? Is space in fact not quite nothing?
|
| # ? Sep 20, 2010 18:31 |
|
|
How do you study? are you one of those people who can be shown a problem once and then do every single thing relating to that problem or do you have to do an assload of problems out of the back of the chapter in order to wrap your head around the concept? I am in the latter boat myself.
|
| # ? Sep 20, 2010 18:39 |
|
|
Kiri koli posted:What field of theoretical astrophysics do you work in? I'm a graduate student as well (a baby grad student about to take the quals, yikes!), but I do observations and mostly work on the high redshift universe/galaxy evolution right now. I work with general relativity. I'd like to not be very specific, because I want this forums account to stay unassociated with my name, so that I can continue to bitch about dumb things my students do in SAP without any chance professional repercussions. Besides, sometimes I say dumb things on the internet and I'd like to remain un-google-able for that reason also. I'm not expecting anyone to bother doing all the detective work to place a name to this account, but it doesn't hurt to be cautious. bigperm posted:Did we ever figure out how elements heavier than iron can form in supernovas? I read a book that was talking about this being a problem... but I never finished it. Basically what happens is that in supernovas there are lots of energetic collisions that happen really, really fast, so you can build up to heavier stable elements even though the in-between elements are pretty unstable. The exact specifics of it are still a field of ongoing research, though. Well, the CMB doesn't seal the deal about the big bang, but it does seal the deal about a homogeneous expanding universe. The CMB is a pretty clear signal that thirteen or fourteen billion years ago, the universe was smaller-scale, denser, hotter, and unusually uniform. We literally can't see what happened before then, but it is natural to construct a space-time where it expands from a very very small very very hot very very dense state, and there are indirect observations (such as the ratio of helium to hydrogen in the universe) which can give us a probe to the times before the CMB was radiated, but as you go backward and the universe gets hotter and denser, our understanding fails and we can't be too sure. helopticor posted:What's your take on the whole mathematics person/physics person rivalry? (I say this as someone with many friends studying/researching physics.) The rivalry doesn't exist among professional, rational people who aren't goddamn idiots. There's no reason for there to be a rivalry, any more than there needs to be a rivalry between butchers and grocers. We're all different parts of the great metaphorical machine, a machine which would suffer if any one part disappeared. My day-to-day research mostly involves reading papers, deriving equations, and coding. So, I guess, it is probably pretty similar to a mathematician. I don't know, I've never been a mathematician. GestureSignalThreat posted:Relativity says space(-time) is curved. How can nothing be curved? Is space in fact not quite nothing? Spacetime is like a surface on which you can place things. You can tell it's curved by the way its geometry works. If you draw a triangle on this surface, do all of its angles add up to 180 degrees? If not, it's curved somehow. It's a difficult concept because it goes against everything you ever learned in grade school geometry. Just as curving a piece of paper affects the things drawn on it, so does curving space affect the things in it - you just have to take that concept one dimension higher (leaving time out of the picture for the moment). IratelyBlank posted:How do you study? are you one of those people who can be shown a problem once and then do every single thing relating to that problem or do you have to do an assload of problems out of the back of the chapter in order to wrap your head around the concept? I am in the latter boat myself. I have a pretty good intuition for how to solve a physics problem, but there's no substitute for practice. Some concepts are easy enough, and some concepts you'll never understand even after you can do all the problems flawlessly. There's no cure for this, as far as I know. My general tips for solving problems are: draw a picture, don't plug in numbers until the very end - leave it all as symbols/variables so that you can avoid rounding errors and check whether it makes sense before plugging in the numbers, and keep track of the dimensionality (units) to make sure that it always makes sense. That's all for today, folks, I've got places to be and things to do.
|
| # ? Sep 20, 2010 18:54 |
|
|
Is there an experiment that can be performed to determine conclusively if the experimenter were within the event horizon of a black hole? If so, has that experiment been performed on earth and what were the results?
|
| # ? Sep 20, 2010 19:53 |
|
|
How were your classmates? When I majored in physics a good portion was normal yet a not insignificant part were basically goon stereotypes (except rail thin instead of fat). Also male:female ratio. I wonder if it is different on the other side of the globe (assuming US).
|
| # ? Sep 20, 2010 20:28 |
|
|
Does Theoretical Astrophysics cover methods for finding extrasolar planets, or is that another field? If it is in your field, are there any upcoming potential developments you've heard about that might increase the rate at which we find extrasolar planets or the details we know about them?
|
| # ? Sep 20, 2010 20:35 |
|
|
I'm a materials scientist and I've taken many physics courses (though mostly thermodynamics and solid state), but I have a really simple question that I've never been able to get a good answer for: So, normally, when an object with mass "m" is accelerated at a constant rate "a" we say that it experiences a force F = ma. If this acceleration is due to, say, being in a car or a centrifuge or whatever, then the resulting force can be measured by an accelerometer or felt by a person, and if the acceleration is strong enough it can even destroy the object being accelerated... But when a free-falling object is accelerated by gravity, there is no such force that can be felt or measured. How was this behavior explained prior to general relativity? Is there a classical explanation? Also, is this "forceless" acceleration unique to gravity or does it apply whenever a field pulls/pushes on all parts of an object simultaneously and equally? If a charged object felt a constant acceleration due to an electric field, would it be in an accelerated reference frame, or could it be considered to be in an inertial reference frame the same way objects experiencing constant acceleration in a gravitational field can be?
|
| # ? Sep 20, 2010 21:02 |
|
|
I've been trying to get my head around the expansion of the universe. Can you tell me if this is a decent layperson's explanation? Imagine we have a flat plane with edges (like an A4 peice of paper), where any point on the plane can be described by a tuple of two coordinates (x, y). It is a 2-dimensional universe. Wrap this plane into the shape of a sphere*, and you still have your 2-dimensional universe, but its curvature means that it is boundless - if you move your point in a single direction, it will eventually come back round to its point of origin. This was still the case with the flat "A4" plane - although it has edges, when you go off one edge, you come back out the other side - but by wrapping it up in a sphere, it will hopefully seem more physically "intuitive". Now remember that even though our curved 2-dimensional plane universe is embedded in 3 dimensions, the only thing that exists is our 2-dimensional universe. Points in space can only exist on the (x, y) plane. If you imagine this surface swelling up like a balloon, you can see that specific points on the surface are moving further and further apart from other points - just as we witness with the radial velocities of distant galaxies. The model for reality extrapolates on this by extending this 2 dimensional surface to 3 dimensions. This is fine with me, despite the fact that I cannot visualise a 3 dimensional surface expanding in 4-dimensional space. Where it gets difficult for me is that, although we imagine we are restricted to 2-dimensions, and the 3rd is not part of our "space-time", doesn't this model suggest that we are embedded in some higher-dimensional space, be it 3-d for demonstration purposes, or 4-d in reality? Or is the simple fact that we cannot access this dimension mean that the concept of space external to whatever our "universe" is constrained to is meaningless? * I understand this is topologically impossible, fundamental group something torus something too complicated to bring into the discussion.
|
| # ? Sep 20, 2010 22:42 |
|
|
Ok, graduate student in aerospace/mechanical engineering checking in. I'll try for the hardest questions I can. What is electrical charge? How is it transmitted? What causes the things that give particles charge to do so? What causes that, etc... What are quarks made of? How would the higgs boson give things mass? What gives it that ability? What happened before the big bang? Is a singularity literally a singularity or is it just really really small? Why does the speed of light/plank constant/etc have the value it does? How do we know the universe didn't start 1 second ago, with everything lined up. Ok, this is starting to get ridiculous. Good luck.
|
| # ? Sep 20, 2010 22:56 |
|
|
DontMockMySmock posted:The worst science is easy enough to answer: The Core. This is personally embarrassing because my uncle's company provided a majority of the techno-gizmos that they used to shoot that. They actually do some really amazing things with them in real life - but they also don't do ANY of the things that they showed them doing in the movie (to be fair, I haven't seen it but I hear it's atrocious). Great thread, thanks!
|
| # ? Sep 20, 2010 23:01 |
|
|
Seconding wanting to know about quarks and other subatomic particles (For example: How can one taste a subatomic particle to determine its flavor?). I'm an undergraduate Chem major and anything smaller than protons-electrons-neutrons is a mystery. I've also read a bit on laser interferometers, and would like to ask "What's the deal with gravitational waves?" Thanks!
|
| # ? Sep 21, 2010 00:04 |
|
|
Alright I lied, one more post today. omlette-a-gogo posted:Is there an experiment that can be performed to determine conclusively if the experimenter were within the event horizon of a black hole? If so, has that experiment been performed on earth and what were the results? There is no local experiment that can determine if you are in a black hole; however, large scale observations rule out anything but a black hole jillions and jillions of times bigger than the observable universe, an unlikely concept. An observer in free fall (as we would be, in this enormous black hole) experiences what we call a "local Lorentz reference rame," meaning that for small distances, it behaves as if it was in a flat spacetime. But over larger distances, the curvature resulting from the global geometry becomes apparent. The black hole would have to be big enough such that "observable universe" is smaller than "small distances," where "small distances" is compared to the size of the black hole. So I think it's safe to say that we are not in a black hole. Namarrgon posted:How were your classmates? When I majored in physics a good portion was normal yet a not insignificant part were basically goon stereotypes (except rail thin instead of fat). Also male:female ratio. I wonder if it is different on the other side of the globe (assuming US). Well, mostly we were all pretty nerdy, as you might expect. I am a pretty goony guy myself, unfortunately, and I knew a couple other goony physicists. As for the gender ratio, it was about 4:1 male:female both in my graduating class and my entering grad class. This sort of problem is pretty endemic in western culture, as far as I know. SMBC states the problem pretty succinctly:  Michaelos posted:Does Theoretical Astrophysics cover methods for finding extrasolar planets, or is that another field? If it is in your field, are there any upcoming potential developments you've heard about that might increase the rate at which we find extrasolar planets or the details we know about them? Actually finding them is an experimental issue, and studying them is usually thought of somewhat separate from astrophysics and referred to as "exoplanet studies" or something like that. As for upcoming potential developments, well, we don't need any because we're already discovering them far faster than we know what to do with. Unfortunately we are still discovering mostly the uninteresting (from a science fiction point of view, anyway) gas giant type planets. Only recently have we actually managed to directly see a planet (and as far as I know, just the one); mostly they are discovered by observing partial eclipses, which lead to a characteristic periodic varying of the luminosity of the system. We can tell quite a bit about the planet from this sort of observation: its period of revolution, its approximate size, and its approximate mass. Morbus posted:I'm a materials scientist and I've taken many physics courses (though mostly thermodynamics and solid state), but I have a really simple question that I've never been able to get a good answer for: The curious nature of gravity is something which, in Newton's time, was something of a mystery when people thought about it at all, but which Einstein managed to clear up. The issue is this: the same thing that is the "charge" of gravity, "gravitational mass," also happens to be the same quantity as its resistance to change in motion, aka its "inertial mass." This is one way of stating the Equivalence Principle in general relativity. In freefall, all bits of matter are accelerated evenly, and so there is no stress nor strain in the composite object. When some other force pushes the object, each bit of object has to push the next, and so on. If you had a collection of electric charges such that the charge density was everywhere proportional to the mass density, you'd see a similar effect in the influence of a constant electric force, since then the electric charge would be similarly proportional to the inertial mass. Of course, that's all for constant forces, and you CAN feel gravity even in freefall if the force isn't constant - you get "tidal" effects because the force is no longer equal everywhere in the object. oiseaux morts 1994 posted:I've been trying to get my head around the expansion of the universe. Can you tell me if this is a decent layperson's explanation? You don't have to think about it as a two-dimensional sheet expanding in three dimensions. Instead a better picture would be this: extend your piece of paper to infinity in all directions. Draw a grid of dots on it. Now, stretch it by a factor of two, so that the distance between each dot and its neighbor doubles. THAT is a good picture of what the expansion of the universe is like, and you never needed to think about the third dimension. It's also easy to extend to three dimensions without having to think four-dimensionally: just make it a 3D grid throughout all space, and expand that. That is what the expansion of space is like. The math to describe this is actually pretty simple once you know a little bit of relativity. Catdonkey posted:Ok, graduate student in aerospace/mechanical engineering checking in. I'll try for the hardest questions I can. Hoo boy! Catdonkey posted:What is electrical charge? How is it transmitted? What causes the things that give particles charge to do so? What causes that, etc... Electrical charge is a property that some things have that makes it obey a set of rules that we call the "electromagnetic interaction." It is transmitted by particles that have charge. Particles just have charge, there's no explanation for it - it's almost a philosophical question (but maybe not). The tree of "why"s has to stop somewhere and that's where it stops according to our current understanding. Catdonkey posted:What are quarks made of? Magic. But seriously, in our current model, quarks are fundamental - not made of anything smaller. Other fundamental particles include electrons, neutrinos, photons, and a few more exotic ones you may or may not have heard of. Catdonkey posted:How would the higgs boson give things mass? What gives it that ability? Basically, in the Standard Model of particle physics, everything is described in terms of fields, which are a lot like the electromagnetic field (for example). The fields permeate all of space, and quantum excitations of these fields are particles (for example, a quantum of excitation of the electromagnetic field is a photon). Like electromagnetic waves (photons aka light), the excitations (particles) of these fields ought to travel at the speed of light and be massless. But they are slowed down and given inertia by their interaction with the Higgs field. Fields which do not interact with the Higgs field have corresponding massless particles - electromagnetism's photons and the strong nuclear force's gluons are the only two. An excitation of the Higgs field is called a Higgs boson, and is a natural consequence of the theory. Catdonkey posted:What happened before the big bang? What happened after tomorrow but before yesterday? There is no such time. Catdonkey posted:Is a singularity literally a singularity or is it just really really small? What you mean is, "does a black hole actually have a singularity or just something very compact?" The short answer is, "not only do we not know, we can never know and it can't ever matter that we don't." Anything inside an event horizon cannot influence anything outside an event horizon - that's the definition of an event horizon. The standard simple mathematical picture of a black hole is called the "Schwartzchild metric," and in this picture, a black hole is a literal singularity of infinite mass density. But just because a spacetime looks like Schwartzchild spacetime outside some radius doesn't guarantee that it'll look like Schwartzchild spacetime within that radius. For example, a spacetime that contains nothing but a hollow spherical shell of matter looks like Schwartzchild outside the shell and like flat space inside the shell. But, if the inside of a black hole is made of anything that makes sense, it is a consequence of general relativity that the matter continue to condense and condense until it is of infinite density. I'm not sure that explanation makes sense, let me know if you want to hear more about it. Something to keep in mind in this discussion is that "singularity" doesn't mean "a point of infinite density," it just means "a point where the coordinate system breaks down," and having infinite density is a sure way to do this. Schwartzchild coordinates have a singularity at the event horizon, for example, but transforming to a different coordinate system can remove it. The singularity at the center, however, cannot be removed no matter what coordinate system you transform into. As another example, a simple model of a rotating black hole, the Kerr metric, has a singularity that is ring-shaped at the center. Catdonkey posted:Why does the speed of light/plank constant/etc have the value it does? Why not? Catdonkey posted:How do we know the universe didn't start 1 second ago, with everything lined up. Because that would be incredibly silly! Chard posted:Great thread, thanks! No problem! I'm enjoying it! MattLochNessMonster posted:Seconding wanting to know about quarks and other subatomic particles (For example: How can one taste a subatomic particle to determine its flavor?). I'm an undergraduate Chem major and anything smaller than protons-electrons-neutrons is a mystery. "Flavor" doesn't mean literal flavor. It means "variety" or "type." Neither does the color charge of quarks and gluons refer to literal color. The objects involved are much too small to have either literal color or literal flavor. Sometimes physicists can be pretty dumb about naming stuff! One more SMBC, for funsies:  As for gravitational waves, well, that's a complicated subject. Basically, as massive objects move around, they distort spacetime. Certain types of distortions can propagate like waves, except different. They travel at the speed of light. They're a lot like light waves in that respect. They can be observed by how they cause a periodic stretching of spacetime. A gravitational wave passing through a ring of free masses would cause them to move like this:  which is analogous to how a light wave will move a free charged particle up and down (that's how antennas work). Gravitational wave interferometers use only two axes instead of a whole ring as in that picture, but the concept is the same - one arm will get shorter while the other gets longer, and vice versa, in a periodic motion. How much the masses move depends on how far apart they are - the further apart, the more they move, so your interferometer is better the bigger it is. LIGO, the Laser Interferometer Gravitational-wave Observatory, has two interferometers of arm length 4 km, one in Washington and one in Louisiana. You need at least two for several reasons, mainly so that when you detect something you have independent confirmation of it in the form of a simultaneous signal in the other detector, and so that some idea of what direction it came from can be determined. The other important thing is how does an interferometer detect these small changes in the arm length, anyway? Basically, they use the interference of coherent (laser) light waves bouncing within the arms to detect very small motions as changes in the interference pattern. It's more complicated than that, because of quantum, but that's the gist of it. The problem is that gravitational waves aren't the only thing moving those mirrors around - there's also seismic vibrations, logging that goes on in Washington, traffic from the nearby freeways, animal activity, etc. If a sparrow lands on the detector tube, it produces the equivalent of an earsplitting scream compared to the undetectable whisper of gravitational waves. That's how incredibly sensitive these things are, and yet we still haven't found gravitational waves. So why are we still so confident that they exist? Well, they'd pretty much have to exist to be consistent with every other observation relating to general relativity, unless someone manages to come up with a better theory. There's also one place where gravitational waves have been indirectly observed: the Hulse-Taylor binary pulsar. A binary star system is one system that ought to radiate GWs, and this radiation ought to carry away energy, causing a change in the orbit of the binary. The Hulse-Taylor binary has been observed to be slowing down in a manner consistent with energy loss to GWs. There could be other ways for this to happen, though, so it's not a smoking gun for GWs, just fairly compelling evidence. A direct detection would be so much better, though.
|
| # ? Sep 21, 2010 00:33 |
|
|
Will we ever have artificial gravity-creating devices? Will there ever be significant breakthroughs when in comes to batteries?
|
| # ? Sep 21, 2010 01:22 |
|
|
I'll be the 14 year old and ask "Could a lightsaber actually exist"?
|
| # ? Sep 21, 2010 03:12 |
|
|
Can you explain what a magnitar is and how it forms? Also whats on the cutting edge of cosmological discoveries in terms of celestial bodies? Any new ones that bend the laws of physics beyond black holes? Edit: Im jealous of your conviction and understanding of the subject. I wish I understood the more basic concepts better. Physics 1 & 2 as an undergraduate have given me hell, but the stuff you're doing sounds awesome.
|
| # ? Sep 21, 2010 03:16 |
|
|
What the gently caress is "spin". Like I know its some basic property of particles, but I feel like an idiot every time its brought up in the textbooks. I know it should be simple but somethings not clicking for me. Help me out please. I can't imagine its something as simple as the particle rotating. Or is it? pleease help me Also, why does spin matter? quote:Sometimes physicists can be pretty dumb about naming stuff! One more SMBC, for funsies: Oh don't worry, biologists aren't immune by any means, looking at you Sonic the Hedgehog gene... Yiggy fucked around with this message at Sep 21, 2010 around 03:37 |
| # ? Sep 21, 2010 03:16 |
|
|
Canine Blues Arooo posted:I'll be the 14 year old and ask "Could a lightsaber actually exist"? I don't mean to step on anyone's toes by linking this, but here: http://www.youtube.com/watch?v=xSNubaa7n9o
|
| # ? Sep 21, 2010 03:41 |
|
|
What current astrophysical experiment(s) are you most excited about? Can you explain inflation? I think I more or less understand why we need inflation and am familiar with some of the testable/tested predictions of the theory, but how/why did it happen? Also, what the hell is quintessence?
|
| # ? Sep 21, 2010 03:52 |
|
|
What do you think about Max Tegmark's multiverse? I am an aspiring astrophysicist finishing up my gen eds and his multiverse puts me at the most ease philosophically. My real interest in studying astrophysics is the philosophical part and trying to discover as much as I can about existence. When I get further into my studies, should I be expected to hide this multiverse hullabaloo? It seems to me that many scientists aren't going to want to be bothered with untestable theories. synapse fucked around with this message at Sep 21, 2010 around 04:55 |
| # ? Sep 21, 2010 04:52 |
|
|
Good batch of questions this time!lllllllllllllllllll posted:Will we ever have artificial gravity-creating devices? If you count the possibility of ever building structures large enough to have significant gravity, then yes. Otherwise, no. The only way we know of to have gravity is to have mass, and because gravity is so weak, that means we'll something really friggin' big to do anything significant. As for batteries, you'd be better off asking a chemist/materials scientist. Making better batteries is just a matter of having materials with more disparate reduction potentials. Possibly some space-age nanoengineered crazy material will help someday, I don't know. Canine Blues Arooo posted:I'll be the 14 year old and ask "Could a lightsaber actually exist"? So, to shatter your hopes and dreams, it's pretty clear from how lightsabers behave that they are not made of light. There's no way to make light that ends the way a lightsaber does. But, a lightsaber behaves an awful lot like a hot plasma. First off, it's pretty hot. Secondly, it glows various colors: neon plasma is red, argon plasma is purple, for example. This is the result of different emission lines in the spectrum of the gas. A plasma can be contained as a lightsaber is with very strong magnetic fields, which the charged particles of the plasma can't penetrate. This also explains how they deflect blaster bolts, since blaster bolts also behave like plasma and would be deflected by the magnetic fields. Unfortunately it would take ridiculous quantities of power and engineering beyond current or foreseeable capabilities to produce such a thing. So much power that you might as well just direct that power at your enemy instead. Lastly, it wouldn't even be nearly as destructive as is shown in the movies - passing a lightsaber through someone's arm would give them burns but not sever it. Basically, there's a cool physics idea in there somewhere, but ultimately it's pretty fantastical. onemanlan posted:Can you explain what a magnitar is and how it forms? Also whats on the cutting edge of cosmological discoveries in terms of celestial bodies? Any new ones that bend the laws of physics beyond black holes? A magnetar is just a pulsar with a very strong magnetic field. It is theorized that such an object would, through its magnetic self-interactions, emit x-rays and gamma rays, in a similar periodic fashion as pulsar radio emissions. It's not known conclusively, as far as I know, whether such an object actually exists, or perhaps is a stage in the life of a pulsar, or what. There are some good candidates out there, though. Black holes remain the kings of astrophysics wackiness. People who do gravitational wave detection are particularly interested in binary black hole systems, with two holes orbiting each other, since they are a particularly strong source of gravitational waves. So that's pretty cool. Also, active galactic nuclei are pretty cool; they are supermassive black holes at the centers of galaxies that are surrounded by a hot disk-shaped cloud of material that is spiraling inward, radiating super-strong in the radio spectrum as it does so (strong enough that we detect them billions of light years away - they used to be called "quasars," for quasi-stellar radio source, although we now know they are nothing like stars). Yiggy posted:What the gently caress is "spin". Like I know its some basic property of particles, but I feel like an idiot every time its brought up in the textbooks. I know it should be simple but somethings not clicking for me. Help me out please. I can't imagine its something as simple as the particle rotating. Or is it? So when you have an object going around an axis, or spinning about an axis, it has some angular momentum - a "quantity of rotation" as Newton might put it (he called linear momentum "quantity of motion"). The angular momentum is related to how massive it is, how fast it's spinning, and its moment of inertia about that axis. Angular momentum is important because it is conserved: in any interaction, the amount of angular momentum of the entire system does not change (although angular momentum can be transferred from one thing to another). Angular momentum is a useful concept in calculating orbits, for example, since an object in orbit always has the same angular momentum. That all makes perfect sense (even if I didn't explain it all), and no one has any problem with it. Then we start talking about quantum mechanics. Well, it turns out that angular momentum is quantized - it only comes in parcels of h-bar/2, where h-bar is the reduced Planck constant. It also turns out that most particles have angular momentum, and their value of angular momentum is always the same: it is intrinsic to the particle. This intrinsic angular momentum is called "spin." Again, it is important because it is conserved, but now also for other reasons that have to do with crazy quantum things. If you've learned some chemistry, you might remember "electron configuration notation," stuff like "1s22s22p3". Here each set of three characters represents three pieces of information: what is the energy of this electron, what is the angular momentum of this electron, and how many electrons have that energy and angular momentum. Each electron in an "s" orbital has orbital angular momentum 0, the "p" orbitals have orbital angular momentum h-bar, and so on: "d" is 2 h-bar, "f" is 3 h-bar. This isn't spin, this is just ordinary angular momentum associated with an orbit, just like classical planets or something. However, each of these electrons also has another bit of angular momentum: their intrinsic angular momentum, or "spin." All electrons have spin 1/2 h-bar. Now, angular momentum is a vector quantity, and can be pointing in any direction. So you might think that if you measure the angular momentum along an axis, you could get any value based on the angle between that axis and the angular momentum of the particle. Nope! You always get a value in the set {-s, -s+1, -s+2, . . . s-2, s-1, s}, where s is the spin in units of h-bar. For example, an electron with spin s = 1/2, if you measure its angular momentum along an axis, will always give you the result 1/2 or -1/2 (sometimes called "spin up" and "spin down"). A spin = 1 particle, such as a hydrogen atom, will give you either 1, 0, or -1. And so on. This property has endless repercussions which I won't get into here. So basically, spin is some pretty weird stuff. I only tell you all this to give you a sense of how incredibly weird quantum mechanics really is. And we haven't even gotten into the "spin statistics theorem" that relates spin to the Pauli exclusion principle. . . . To answer your last question, it matters a LOT, for lots of different reasons; it's a ubiquitous concept in quantum mechanics. This is all a roundabout way to answer your question, "I can't imagine its something as simple as the particle rotating. Or is it?" It's not. If you imagine the electron is rotating to give you that spin, and you pretend for the moment that it must be some sort of classical arrangement of mass, and you let this arrangement be as big as possible without violating our observations (which all point towards the electron being, at best, very very very very small), then some portion of the electron MUST be moving faster than the speed of light for it to have this angular momentum. But that violates special relativity. So it can't be as simple as the particle being some sort of rotating thing. It's just yet another inexplicable intrinsic property. manifold posted:What current astrophysical experiment(s) are you most excited about? LIGO, the big effort to detect gravitational waves that I mentioned before, is pretty cool. CDMS, the Cold Dark Matter Search, is an effort to directly detect interactions between dark matter and detectors on Earth. The James Webb Space Telescope, basically Super Hubble, is pretty important if for no other reason than astrophysics has to keep supplying pretty pictures to keep its funding. BICEP-2, a project to detect the polarization of the cosmic microwave background, is probably going to end up being pretty important. LOFAR, the Low Frequency Array, and MWA, the Mileura Widefield Array, are a couple of experiments attempting to look for the signal of neutral hydrogen in the early universe that existed before galaxies and stars formed. There are a couple cosmic-neutrino detection experiments, whose names escape me, which could have important results relating to supernovae. Those are the ones that I can think of off the top of my head. There's plenty more, of course. Inflation is sort of a hand-waving way to explain why the cosmic microwave background is so incredibly uniform. You can look at the CMB and it's all almost exactly the same temperature. So these different patches of sky must have been in thermal equilibrium at some point. But, if you follow the expansion of the universe backward in a logical way, these different patches couldn't have ever been causally connected! They are so far apart and they expand so fast that even information traveling at the speed of light is not enough to get them into thermal equilibrium. So, we postulate that this model is wrong; instead they must have been connected at some point, then suddenly expanded at a ridiculous rate to become causally disconnected as we see them now. This period of ridiculous expansion is called "the epoch of inflation," and we basically know absolutely nothing about it. Quintessence, meaning "fifth essence," is among the names Aristotle gave the "fifth element" that was meant to be loftier even than fire; it composed the heavens; it was also known as "aether" (pronounced the same way as the chemical "ether," FYI, every Magic: the Gathering nerd ever gets this wrong and it is a constant source of minor annoyance). But that's probably not what you're talking about. Quintessence in modern physics is a theory that attempts to explain dark energy. I don't know a whole lot about it, but in cosmology, all you really need to know about the theory is one number: called "w," it is the "equation of state parameter" which relates the pressure to the energy density of a material. Basically, in cosmology, you've got radiation, with pressure equal to one-third its energy density (w = 1/3), matter, with pressure negligible (w = 0), and dark energy, with negative pressure (w < 0) (I know that doesn't make sense, but bear with me). The simplest theory of dark energy is the "cosmological constant," with w = -1. Quintessence has w = -1/3. That's basically all I can tell you about it, unfortunately, as this is not my area of expertise. Does it exist? Is it the ultimate explanation of dark energy? No one knows yet. Of course, now someone has to ask me "what's dark energy?" Or maybe you all already know since it's talked about in popular science a lot. Basically, it's something that must exist to help explain why the universe is the shape it is (flat, or drat near), and why it keeps expanding (at an increasing rate, no less), while still being within the realm of general relativity. It may be that general relativity is ripe for an overhaul, instead, between dark energy, dark matter, and the nondetection of gravitational waves. . . but no one has had any luck with it yet. synapse posted:What do you think about Max Tegmark's multiverse? I am an aspiring astrophysicist finishing up my gen eds and his multiverse puts me at the most ease philosophically. I don't know anything about it, and can't really be bothered right now, but I am generally suspicious of anything that predicts things that we not only can't observe, but can never observe, such as "other universes." I don't know whether Max Tegmark's crazy theories are like that, but I do know that it certainly isn't multiverse theory that pays the bills. I don't think there is anything wrong with a little philosophy, though, and I don't think anyone will look down on you for dabbling in it. So long as you don't soliloquize about it at parties or anything.
|
| # ? Sep 21, 2010 06:27 |
|
|
DontMockMySmock posted:If you count the possibility of ever building structures large enough to have significant gravity, then yes. Otherwise, no. The only way we know of to have gravity is to have mass, and because gravity is so weak, that means we'll something really friggin' big to do anything significant. How does mass work near the speed of light? What if there was some kind of machine that rotated or used some sort of centrifugal spinning thing to increase its mass (as in near the speed of light)? I guess what i'm trying to ask is if the mass of an object traveling near the speed of light only has its mass increase apparent to its own reference frame or does it increase in all reference frames? You could probably build some sort of gravitational slingshot engine if you shoot out some sort of device that spins up a mass to near the speed of light, effectively making however much mass as you want, and therefore gravity. Then your spaceship or whatever would be accelerated to the device due to gravity. You could then spin down the device and store its energy in some kind of battery. Pick up the device as you fly by and start the whole process over again. I'm thinking the thing i'm missing here is the energy required to spool up the device would effectively be infinite because you want to spin it up as close to the speed of light as possible so it would take an infinity large battery to store the energy. The energy used to shoot out the device could also be stored and recovered somehow, especially since it wouldn't have nearly as much mass as it does when its spinning. Seems like one of those things you might have to do the calculations on to know. vvv Nothing in my post goes over the speed of light. (its a four stroke gravity engine: shoot, spool up, attract, spool down  )
SanitysEdge fucked around with this message at Sep 21, 2010 around 07:38 |
| # ? Sep 21, 2010 07:03 |
|
|
My understanding is that faster-than-light travel may not necessarily be possible, but recent experiments have implied that faster-than-light information transmission is possible - the experiments having to do with transmitting quantum spin over distances of several kilometers, if I remember correctly. How groundbreaking are those experiments and/or what are their implications?
|
| # ? Sep 21, 2010 07:19 |
|
|
Is it accurate to say that the existence of quantum indeterminacy demonstrates that the law of mass/energy conservation does not actually apply at the quantum level (regardless of whether or not we can actually use that fact to get free zero-point energy or whatnot)?
|
| # ? Sep 21, 2010 07:34 |
|
|
|
| # ? May 20, 2013 02:06 |
|
|
Ion drive as a plausible means for space travel over extremely long distances? Also, ignoring the whole running-into-a-rock problem, do there exist any theoretical problems regarding people traveling at a significant fraction of c? Does quantum entanglement allow for the possibility of the ansible (from Orson Scott Card's books, basically faster-than-light communication) or some other form of "faster than light" communication, even if it involves previous preparation? I know you don't want to say more about what you do, specifically, but since you've already said you work in general relativity, can you elaborate on the field in general in terms that are relatively easy to understand?  Seriously though, can you please elaborate on what the field of "general relativity" entails?Finally, please add Kim Stanley Robinson's Mars Trilogy (Red/Green/Blue Mars) to your reading list if you haven't read them. They're great.
|
| # ? Sep 21, 2010 07:46 |
|
