The Official Cool Stuff Thread



  • Post your cool stories or videos here.

    Here's what a journey from the sun to Jupiter looks like at the speed of light. It takes 45 minutes!

    (ugh Discourse doesn't support any kind of Vimeo embed and I couldn't find a YouTube equivalent)



  • @mott555 said:

    Here's what a journey from the sun to Jupiter looks like at the speed of light. It takes 45 minutes!

    Nitpick: This is what it would look like if Special Relativity didn't exist 😄



  • @Rhywden said:

    Nitpick: This is what it would look like if Special Relativity didn't exist

    I've taken liberties with certain things like the alignment of planets and asteroids, as well as ignoring the laws of relativity concerning what a photon actually "sees" or how time is experienced at the speed of light, but overall I've kept the size and distances of all the objects as accurate as possible. I also decided to end the animation just past Jupiter as I wanted to keep the running length below an hour.


  • area_deu

    Ice is nice!



  • Since we're doing relativity stuff at the moment, for those who didn't see this the first time round:

    A Slower Speed Of Light – [01:20..09:16] 09:16
    — Scott Manley



  • No; according to the creators of highly regarded science documentary Star Trek Generations, a rocket will reach a planet/sun the instant it naively appears to.

    Star Trek: Generations (5/8) Movie CLIP - The Nexus (1994) HD – [00:45..02:38] 02:38
    — Movieclips



  • Clearly that planet's sun is a small orb 10,000 feet or so in the atmosphere.



  • Better is the explanation that comes a few minutes before, where they explain that the starship that can travel at like 200,000 times the speed of light can't possibly intercept the rocket before it hits the sun. The chemical rocket.


  • Discourse touched me in a no-no place

    It's impressive they managed to simulate a syzygy, too. I know it was mentioned already and I don't care.



  • I am reminded of this 'tediously accurate scale model of the solar system', which is pretty much what it says it is...



  • @Rhywden said:

    Nitpick: This is what it would look like if Special Relativity didn't exist 😄

    I seem to recall Neil deGrasse Tyson explaining that from the point of view of a photon, all travel throughout the universe is instantaneous, so the concept of 'time' doesn't really exist for them. (Not that photons are capable of perceiving this or reflecting upon it, but still...)



  • To extend that, everything (including us) always moves at the speed of light through spacetime. What we perceive as the passage of time is the component of our speed through the time dimension.


  • Discourse touched me in a no-no place

    Yep, and acceleration is really just a rotation.


  • kills Dumbledore

    Time dilates as you get near the speed of light, so the observed time for the traveller is less than that for an outside observer in a non-inertial frame of reference. This is where the "twins paradox" comes from.

    If you accelerate to c, time dilation would make your passage of time 0, so from your POV you would be able to get anywhere in the Universe in 0 time, effectively infinite speed.

    This shows why adding more energy to a moving particle gets it asymptotically closer to c without ever being able to reach it, as from the reference frame of the moving particle it is being sped up to a larger but still finite speed. It would take infinite energy to accelerate anything with mass to c, at which point the equations of relativity break down as there's a division by 0 involved.

    Interestingly, there's nothing in the maths to prevent FTL travel except the passing through exactly c. A particle that came into existence travelling FTL wouldn't necessarily break the rules of physics. I'm now probably purely in the range of pseudoscience,, but if you were close enough to c, I can't see why it wouldn't be possible for quantum uncertainty/tunnelling to jump you over the light barrier without passing through it.



  • @Jaloopa said:

    noon-inertial

    Let's not bring time zones into this.


  • kills Dumbledore

    Dammit. I rely on speel check to catch the random extra characters my keyboard likes to insert. Making a word into a different word isn't playing fair


  • Discourse touched me in a no-no place

    @tar said:

    (Not that photons are capable of perceiving this or reflecting upon it, but still...)

    It's a good thing you included this disclaimer, otherwise @another_sam might accuse you of believing in magic.



  • @Jaloopa said:

    If you accelerate to c, time dilation would make your passage of time 0, so from your POV you would be able to get anywhere in the Universe in 0 time, effectively infinite speed.

    Well, there's the small problem of lightspeed resulting in a "divide by zero" situation when using the formula for time dilation 😄


  • Discourse touched me in a no-no place

    @Rhywden said:

    Well, there's the small problem of lightspeed resulting in a "divide by zero" situation when using the formula for time dilation 😄

    It works better when you switch to a spacetime vector representation. Acceleration really is a rotation, but the time dimension is… different.



  • Doesn't that still yield a singularity when approaching c because even in the vector form you still have the skalar Lorentz factor in there (which does have this pesky 1-v²/c²)



  • So you don't have to reach c, you just have to get close enough that travel from any point in the universe to any other point seems like a few seconds.


  • SockDev

    just make sure you don't hit ANYTHING while traveling at that speed. even a single proton carries enough energy to be pretty damn fatal when traveling in excess of .99c relative to you.



  • @mott555 said:

    So you don't have to reach c, you just have to get close enough that travel from any point in the universe to any other point seems like a few seconds.

    Yes, but the point was what happens at exactly c and not almost c.

    Almost c we can deal with pretty well, after all, it's pretty much the only reason we see muons on earth 🙂



  • @accalia said:

    just make sure you don't hit ANYTHING while traveling at that speed. even a single proton carries enough energy to be pretty damn fatal when traveling in excess of .99c relative to you.


  • area_deu

    In other words, not fatal, but painful?



  • @aliceif said:

    In other words, not fatal, but painful?

    100 km/h baseball to the noggin? While that may be survivable I certainly won't nominate myself to try that one out.



  • I wonder what the chances are of a proton passing through your body at that speed without interacting with anything. We are mostly empty space after all.


  • area_deu

    Only one player has died after being hit in the head. Cleveland Indians shortstop Ray Chapman was hit by a pitch thrown by submarine pitcher and noted headhunter Carl Mays on August 16, 1920 at the Polo Grounds in New York. He died 12 hours later and is noted as the only player to have been killed by a pitch. The following spring, Chapman's teammates experimented with leather helmets similar to those being used by football players; that year's Spalding Guide declared, "There is nothing 'sissy' about it." Catcher Roger Bresnahan is cited as one of the first players to construct and wear a helmet, in 1907.


  • Discourse touched me in a no-no place

    @Rhywden said:

    Doesn't that still yield a singularity when approaching c because even in the vector form you still have the skalar Lorentz factor in there (which does have this pesky 1-v²/c²)

    Well, strictly you're using the wrong norm there. Couching it in terms of rotations really works, but it's brain-bending.

    In the real world, you don't have to worry about the singularity because it would take you an infinite amount of energy to accelerate anything to c (because mass is not constant). Only massless entities (strictly, entities without a rest mass) can move at c and when going at that speed, experience no time elapsing. We only found out that neutrinos have mass because they were observed oscillating, i.e., that time elapsed for them.



  • @mott555 said:

    I wonder what the chances are of a proton passing through your body at that speed without interacting with anything. We are mostly empty space after all.

    Not that small. While I'm unwilling to dig out an article on how to calculate the cross-section of someone's body, I'd posit that we could compare it to radioactive rays. Let's also posit that the speed doesn't matter (we're talking about a single particle here and not a whole bunch of them).

    I'd put the proton particle's collision chances between that of an alpha particle (essentially a Helium nucleus) and a beta particle (an electron/positron). Since a proton is not an elementary particle it thus possesses an actual radius which would put it more on the alpha end of the collision probability spectrum than the beta one.

    The penetration depth for alpha particles in nearly anything is mere millimeters while beta achieves several centimeters.

    Edit: Scratch that, I'm still whoozy from my stay at the hospital. The penetration depth is indeed dependant on the speed/energy of the particle. For electrons, a summary can be found in this paper, protons should still have a higher chance of interactions, though: http://www.microscopy.ethz.ch/downloads/Interactions.pdf


  • Discourse touched me in a no-no place

    @Rhywden said:

    Edit: Scratch that, I'm still whoozy from my stay at the hospital. The penetration depth is indeed dependant on the speed/energy of the particle. For electrons, a summary can be found in this paper, protons should still have a higher chance of interactions, though: http://www.microscopy.ethz.ch/downloads/Interactions.pdf

    It also depends on the charge. Neutrons and protons have about the same mass and energy spectra, but neutrons are far more penetrating because they don't couple to the electromagnetic fields of the molecules that they're passing through.



  • @dkf said:

    Well, strictly you're using the wrong norm there. Couching it in terms of rotations really works, but it's brain-bending.

    In the real world, you don't have to worry about the singularity because it would take you an infinite amount of energy to accelerate anything to c (because mass is not constant). Only massless entities (strictly, entities without a rest mass) can move at c and when going at that speed, experience no time elapsing. We only found out that neutrinos have mass because they were observed oscillating, i.e., that time elapsed for them.

    I never liked that field stuff much, though one of my professors managed to explain statistical mechanics absolutely brilliantly - almost all of us managed to pass on the first try. The next professor in field theory was the absolute opposite - his homework consisted of "Either you're a genius level physicist or you have to root through the library until you find the solution to this problem in an obscure book from 1953 written in French", his lectures were chaotic and he was an absolute bastard. This guy thought that all Physics after Newton was rubbish and that Einstein was a fraud. The university's dean had a restraining order against him (he wasn't allowed to approch him closer than 200 meters due to a brawl he instigated)

    I also found a recent paper by him where he set out to disprove global warming. He did this by disproving the Greenhouse Effect in its totality. Nevermind that it would be a mite cold without that one here on Earth.



  • I think, I'll share some more stories about this guy. I'm also a bit mystified how he ever made tenure.

    He's shunned by the rest of the Physics department and, yes, that includes his own son who is a very nice guy, by the way.

    He surprised us by knowing all of our names after the 2nd lecture. Granted, we were only 30 students this round but we had never actually told him our names. Just the usual list of attendees we had to sign.

    We had to sign this list only once in the very beginning - he memorized exactly who was attending regularly and who was only going through the motions. This played into his other habit: The homework tasks.

    Those tasks, as I already stated, were fiendishly difficult so for us merely mortals there were two options:
    Copy the solutions from our two geniuses or search for the solution in the library. Both variants rarely resulted in a deeper understanding of the subject matter, however.

    Here comes the professor into play again: The criterium for passing the course was easy - you just had to demonstrate the solution for one of the tasks one single time. He himself would sit in the background and watch our nervous mumblings and scratchings on the blackboard like a hawk.
    Now, if you were a regular attendee and your solution was not too harebrained, then that was it. If you weren't... then he began to ask questions. And not of the "what is your favourite colour" kind.

    The guys responsible for checking our homework were sometimes just as mystified by the tasks as we were, I'd say. I distinctly remember stumbling over one solution in the library, only for it to skip two lines with the accursed words: "Using a simple transformation, we use the result to..."

    Just like the other anathema of any student ("As can be seen easily,..."), such transformations are reliably neither short nor easy. I gave up after filling two pages with scribblings and simply copied those words into my solution. The postgraduate, upon seeing this line, merely nodded sagely and said: "Ah, yes, well done."

    Good times.



  • @Rhywden said:

    100 km/h baseball to the noggin? While that may be survivable I certainly won't nominate myself to try that one out.

    I wouldn't recommend that. I've had something like that happen to me. Fortunately, I have a really hard head, and it hit me pretty square on the eye socket.


  • Discourse touched me in a no-no place

    @Rhywden said:

    The guys responsible for checking our homework were sometimes just as mystified by the tasks as we were, I'd say. I distinctly remember stumbling over one solution in the library, only for it to skip two lines with the accursed words: "Using a simple transformation, we use the result to..."

    Just like the other anathema of any student ("As can be seen easily,..."), such transformations are reliably neither short nor easy. I gave up after filling two pages with scribblings and simply copied those words into my solution. The postgraduate, upon seeing this line, merely nodded sagely and said: "Ah, yes, well done."

    You could have used “It is obvious that…” too. You can hide some huge sins behind that phrase.



  • @boomzilla said:

    I have a really hard head, and it hit me pretty square on the eye socket

    As someone who's not been on the receiving end, the eye socket sounds worse.



  • @loopback0 said:

    As someone who's not been on the receiving end, the eye socket sounds worse

    I think the structure of it probably helped. Nothing was broken, not even a concussion (according to the emergency room). My eye was swollen for a few days.



  • @Rhywden said:

    This guy thought that all Physics after Newton was rubbish and that Einstein was a fraud. The university's dean had a restraining order against him (he wasn't allowed to approch him closer than 200 meters due to a brawl he instigated)

    How the heck did he manage to keep his job?

    @Rhywden said:

    I also found a recent paper by him where he set out to disprove global warming. He did this by disproving the Greenhouse Effect in its totality. Nevermind that it would be a mite cold without that one here on Earth.
    How the heck did he manage to get that published?


  • Discourse touched me in a no-no place

    @HardwareGeek said:

    How the heck did he manage to get that published?

    I'd guess that it's just a matter of picking the right venue. Some places will publish anything as long as the fee has been paid, and other places (think oil company house journal) are naturally more receptive to people pushing the anti-AGW line. Merely being published doesn't count for all that much; what counts is where and who is citing you.



  • Isn't the entire point of peer-reviewed research that it gets published in a place where people can review it and then after the reviewing process someone can decide whether it's a valid result or not?


  • Discourse touched me in a no-no place

    @ben_lubar said:

    Isn't the entire point of peer-reviewed research that it gets published in a place where people can review it and then after the reviewing process someone can decide whether it's a valid result or not?

    The peer reviewing process itself (in a properly functioning system) does a lot of checks as to whether what the author(s) report is plausible. It's one of the more acceptable reasons as to why getting a journal paper out takes so fucking long…

    The exact nature of the checks will vary by journal and discipline. In computing and software engineering, redoing many of the results as part of the checks is often quite possible; the challenge is typically in the picking of what is the right approach in the first place. In other disciplines, it's still relatively easy to check the information processing parts of the paper (typically quite a large fraction for non-bioscience papers) even if redoing the lab parts or data collection parts is difficult. And it's always relatively easy to check the line of the argument in a paper; does what they claim follow from the evidence presented? After review, usually by 2 or 3 people who are experts in the field, the reviewers' comments get passed back to the author for comments and corrections (assuming they didn't recommend a flat rejection) and the updated version goes back to the reviewers to let them check that things are at least better than they were (even if not perfect ;)).

    The cases I'm aware of where there were significant problems are where there was something wrong in the stages of research that are very difficult to check during review. Things like basic data custodianship or just making a bad blunder in the choice of analysis — the latter isn't always picked up by reviewers — will come under this category, and those are where you see things like retractions by the authors or, rarely, by the journal itself (which is usually indicative of something of a scandal, and may well make the newspapers; it's also rare). I sometimes think that it's a good thing the journals are going online; it makes it much easier to Google for the text, figures and diagrams when looking for plagiarism. 😃

    The issue that I was alluding to was that some publishing venues are less scrupulous than that. Their reviewing process might just include an examination of a fee (so everyone and his monkey can get in, and frequently does just that; try searching for auto-generated joke papers sometime). There's also company house journals; they can be very good (some of the old IBM journals are a gold-mine for chip design techniques even now) but are often strongly slanted towards what benefits the company as all the papers they publish have at least one company employee among the lead authors. Caveat emptor.


    [spoiler]Dis[/spoiler]claimer: I've both written and reviewed papers, both for conferences and for journals in both cases. All in software engineering.



  • @HardwareGeek said:

    How the heck did he manage to keep his job?
    How the heck did he manage to get that published?

    Tenure.

    I have no idea. This is the paper, by the way: http://arxiv.org/pdf/0707.1161.pdf


  • Discourse touched me in a no-no place

    @dkf said:

    (typically quite a large fraction for non-bioscience papers)

    Before anyone claims I'm casting aspersions here, the difference with bioscience papers is that they're mostly very short (1, maybe 2 pages). It absolutely drives me round the twist how you can't get into really describing in detail what you did and why it is interesting, but that's the style in the field. I usually need at least 8 pages, and often 10 or more, and my paper writing style is usually criticised by reviewers for being a bit too densely packed. 😉

    Ah, the fun of multidisciplinary working…


  • Discourse touched me in a no-no place

    @Rhywden said:

    This is the paper, by the way: http://arxiv.org/pdf/0707.1161.pdf

    115 pages! Dear god in heaven, that's not a paper, that's a direct attack on the world supply of wood-pulp (or would be if it was printed out). A short rebuttal of at least some of it is at http://arxiv.org/pdf/0802.4324v1.pdf and a longer one is off of http://dx.doi.org/10.1142/S021797921005555X (that's paywalled), the abstract of which is pretty damning, as it accuses the original paper authors of cardinal sins like only applying fundamental physical laws to part of the problem.

    Heh. I've just looked up the impact factor of the International Journal of Modern Physics B, and it's “not very good”. As in, I wouldn't publish there, even if I had something relevant to the journal topic. Oh dear… 😃



  • Yeah, Realclimate.org also did a number on that piece.

    They claim that radiative heat transfer from a colder atmosphere to a warmer surface is forbidden, ignoring the larger transfer in the other direction which makes the complete process allowed.

    That's from your 2nd link. They really didn't get the whole equilibrium shtick, did they?


  • Discourse touched me in a no-no place

    @Rhywden said:

    > They claim that radiative heat transfer from a colder atmosphere to a warmer surface is forbidden, ignoring the larger transfer in the other direction which makes the complete process allowed.

    That's from your 2nd link. They really didn't get the whole equilibrium shtick, did they?

    Quite apart from the fact that we're dealing with non-equilibrium processes in the first place, there's also the shifting back and forth between classical scale and quantum scale physics. The types of description that you use at the two scales are very different (e.g., heat is a classical scale phenomenon, and the laws of thermodynamics only apply statistically at the quantum scale because of quantisation effects) and you have to be ever so careful when mixing the two.



  • On a macroscopic level this should very well be an equilibrium.


  • Discourse touched me in a no-no place

    @Rhywden said:

    On a macroscopic level this should very well be an equilibrium.

    Sort of. We've got this thing called “weather” which illustrates that the equilibrium is only a sort of thing. 😄 Non-equilibrium processes are demonstrations that there's more to physics than simple models. They usually seem to involve fluid dynamics (or, even better, magnetohydrodynamics; that's for people who think that fluid dynamics is too simple and easy to understand…)


  • BINNED

    @dkf said:

    (or, even better, magnetohydrodynamics; that's for people who think that fluid dynamics is too simple and easy to understand…)


    Filed under: I hate fluid dynamics


  • BINNED


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