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Jim Silly-Balls posted:Moving at all equates to time travel, it only becomes noticeable as you approach C I’m moving through time at a rate of one second per second.
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Jun 23, 2021 14:45
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Jim Silly-Balls posted:Moving at all equates to time travel, it only becomes noticeable as you approach C The closer you get to c, the less you travel in time.
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Jun 23, 2021 20:38
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Lol, just imagine thinking space and time are two separate thing. Hard lol.
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Jun 23, 2021 23:30
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Thing I never got was how that rule doesn't imply the existence of an objective "at rest" Unless I suppose time is also somehow subjective and the difference is just that you perceive things moving differently through it as they move geographically.
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Jun 24, 2021 00:27
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You’re only ever at rest relative to something else. There is no pure frame of reference for “no movement” as far as we know in the universe
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Jun 24, 2021 00:50
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OwlFancier posted:time is also somehow subjective Relative
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Jun 24, 2021 01:19
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Platystemon posted:I’m moving through time at a rate of one second per second. Not relative to where I'm standing 
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Jun 24, 2021 03:23
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OwlFancier posted:Thing I never got was how that rule doesn't imply the existence of an objective "at rest" Not "subjective," but relative, yes. List of things that are relative (depend on your reference frame):
List of things that are invariant (constant, regardless of your point of view):
So yeah, time and space are relative. When we say "the faster you move in space, the slower you move in time", we mean that relative to some observer. If you're goin' 60% of c relative to me, and you send out some signals at what you think are 1 minute apart, I'll think that you sent those signals 1.25 minutes apart. To me, it looks like your clock is running slow. However, we both agree that you and your clock have experienced 1 minute. The faster you go relative to me, the more time I will observe between those signals (even after accounting for the signal-travel-time it takes for me to get the signals at all). Similarly, your observations of my clock are identical, since I'm also going 60% of c relative to you. I think your clock is running slow, and you think mine is running slow. This seems like a paradox (usually called the "twin paradox"), but it's resolved once you take into account the fact that we do not agree on which ticks of your clock are simultaneous with which ticks of mine. It all makes more sense if you graph it (that graph uses different numbers btw). The only way for us to agree on that is to meet up at the same place - but for us to be moving relative to one another and yet meet up, someone's gotta accelerate to turn around and head back. Here's a graph about that. This breaks the symmetry between our motions, and whoever did the accelerating is the one whose clock went slower (or of both of us accelerated equally, our clocks read the same). Anyways this is all a bit crazy so feel free to google "twin paradox" for a more in-depth explanation.
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Jun 24, 2021 03:54
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With all the relativity and light speed stuff I kind of understand that a thing moving at light speed will appear to be moving at light speed to all observers (though I might have stated that badly or maybe I don't actually understand at all) but my question has always been if it's all relative and I'm trying to accelerate to light speed vs my origin, which was already moving at light speed vs some other point in space/time, why can't I ever be actually moving through space at greater than light speed vs that 2nd point? Like say point A and point B are moving away from each other at precisely .5c, relative to each other. If I'm at point A and decide to travel away from point B I am instantly traveling at faster than the speed of light relative to point B, right? Is this wrong? Or is it just a stupid thought experiment because nobody gives a poo poo about what's happening at point B? And if I can travel faster than light speed away from point B that basically means, as far as I understand, my journey could never be directly observed by point B? And what about two points moving toward each other at precisely .5c? Surely I can accelerate toward another body and increase my energy on impact? Inspector 34 has a new favorite as of 07:17 on Jun 24, 2021 |
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Jun 24, 2021 07:15
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Inspector 34 posted:With all the relativity and light speed stuff I kind of understand that a thing moving at light speed will appear to be moving at light speed to all observers (though I might have stated that badly or maybe I don't actually understand at all) but my question has always been if it's all relative and I'm trying to accelerate to light speed vs my origin, which was already moving at light speed vs some other point in space/time, why can't I ever be actually moving through space at greater than light speed vs that 2nd point? Let's say I can throw a 60 mph baseball. So if I'm on a train, moving 50 mph to your right, and I throw a baseball also to your right, you, standing in the train station and looking through the train's window, see the baseball as going 110 mph to the right relative to you. In other words, the velocities combine through simple addition. Similarly, if I throw the baseball to the left, you'll see it moving 10 mph to the left. But, it turns out, this is just an approximation. When speeds get near c, the math gets more complicated. Let's say I can shoot a 0.6c space torpedo. So if my spaceship is moving 0.5c to the right, and I fire my torpedo also to the right, then does my torpedo go 1.1c relative to you, observing from Earth? You've heard that nothing can travel faster than c, so this must be impossible. In fact, the torpedo would be going 0.846c relative to you. The formula isn't just: v1 + v2 it's: (v1 + v2)/[1 + (v1*v2)/c2] but in normal everyday life, that denominator is so incredibly close to 1 that it doesn't matter. You will find that if the two velocities are between -c and c, then the resulting velocity will also be within that same interval. So if you're going really fast, and you accelerate to try to go faster, what happens? Well, you get closer and closer to c. And since the way kinetic energy works in special relativity is also different, your energy still increases just as much as you'd expect, but that energy gets you less and less velocity, asymptotically approaching (but never reaching) c.
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Jun 24, 2021 08:14
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I'm not sure I understand that. It looks like if v1*v2 = c^2 then the denominator is 2, so (v1+v2)/2. But that doesn't jive at all to my layman brain's with the idea of v1+v2 collision between two objects travelling at light speed relative to each other, or a third object that launched itself off of either object toward the oncoming body. Why would the relative velocities be cut in half? It seems kind of arbitrary that just because they are approaching or past the speed of light relative to each other that different math is involved. And I'm not saying different math shouldn't be involved, I'm more curious if there's a certain point where it has to be. Where is that point?
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Jun 24, 2021 10:37
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Inspector 34 posted:I'm not sure I understand that. It looks like if v1*v2 = c^2 then the denominator is 2, so (v1+v2)/2. But that doesn't jive at all to my layman brain's with the idea of v1+v2 collision between two objects travelling at light speed relative to each other, or a third object that launched itself off of either object toward the oncoming body. Why would the relative velocities be cut in half? The denominator is 2, but the numerator is 2c. The resulting velocity is c. In fact, if either velocity is c, then the result is c. (v1+c)/(1+v1*c/c^2) (v1+c)/(1+v1/c) (cancel out c in the fraction in the denominator) c(v1+c)/(c+v1) (multiply top and bottom by c) c (bits in parentheses cancel out) Therefore, anything moving at c is moving at c relative to any observer. In other words, if I'm on a train (in a vacuum) moving right and shine a flashlight to the right at speed c, you also see the light as going at c, not c plus 50mph or whatever. There is no arbitrary math - the math is exactly the same for all objects, regardless of how they are moving. And regardless of what object is being observed in what reference frame, its speed is at most c. I'm not really sure what you're talking about with a "v1+v2 collision" and stuff. Can you lay out a specific situation in more detail?
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Jun 24, 2021 11:01
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I don't think I understand this well enough to describe a situation like that. I'm just trying to understand it conceptually at all. But I'll try. If I have two ball bearings heading toward each other, one from from the left at 20mph and one from the right at 20mph, the energy of produced by their collision is equivalent to if one were standing still and the other was going 40mph, right? So the simple v1+v2 scenario. But at what point does that stop being true? Assume they're going 100mph each, or 10,000,000mph each, why do I need to bring c into the equation? How fast do they need to be going relative to each other for that original 20 + 20mph to not work? That's what I mean by arbitrary, is there a specific point where that kind of simple equation doesn't work and we need to bring c into the equation?
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Jun 24, 2021 11:29
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DontMockMySmock posted:Let's say I can throw a 60 mph baseball. So if I'm on a train, moving 50 mph to your right, and I throw a baseball also to your right, you, standing in the train station and looking through the train's window, see the baseball as going 110 mph to the right relative to you. In other words, the velocities combine through simple addition. Similarly, if I throw the baseball to the left, you'll see it moving 10 mph to the left. Inspector 34 posted:I don't think I understand this well enough to describe a situation like that. I'm just trying to understand it conceptually at all. But I'll try. the (v1*v2/c^2) should produce a small number and for most every day things that number (plus 1) is basically 1 so you can ignore the full equation and get by with just v1+v2 like your 20mph baseballs. When the velocities get into big numbers approaching C, you end up with a denominator appreciably larger than 1 which makes the full equation necessary. so when (1+(v1*v2/c^2)) starts getting appreciably larger than 1 is when your 20+20 math no longer works. 500excf type r has a new favorite as of 15:11 on Jun 24, 2021 |
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Jun 24, 2021 11:38
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Inspector 34 posted:I don't think I understand this well enough to describe a situation like that. I'm just trying to understand it conceptually at all. But I'll try. Oh, I see what you're saying. 500excf type r already answered this but to reiterate, when we do 20 mph + 20 mph = 40 mph, we're using an approximation. It's really 39.9999999999999644 mph. That approximation is really, really accurate, for things on the scale of 20mph, but gets less accurate the higher the speeds get. Where exactly you must stop approximating depends on how accurate you need to be.
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Jun 24, 2021 18:17
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Thanks got it! At least, I get the math part.
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Jun 24, 2021 20:43
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OwlFancier posted:Thing I never got was how that rule doesn't imply the existence of an objective "at rest" You’re not the first person to notice this. quote:In physics, the twin paradox is a thought experiment in special relativity involving identical twins, one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more. This result appears puzzling because each twin sees the other twin as moving, and so, as a consequence of an incorrect and naive application of time dilation and the principle of relativity, each should paradoxically find the other to have aged less. https://en.wikipedia.org/wiki/Twin_paradox
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Jun 24, 2021 22:32
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Phanatic posted:Traveling any faster than c equates to time travel. Yeah relativistic and imaginary ftl travel is amazingly mind bending, and I just thought of something maybe someone smart can confirm/deny for me let's say we invent a drive that let's us Pop out anywhere in the galaxy immediately, and we jump to a star 10 light years away. For us no time has passed, but while we're there we should technically exist 10 years in the future, from Earth's perspective. If someone on earth used a ridiculously strong telescope and watched us at the star right after we popped over, the visual data, our "ring of existence, would need 10 years to reach earth again. Now if we popped back to earth after an hour and then waited that 10 years, we should be able to see ourselves in the telescope, technically existing at two points at the same time, and having travelled back in time when we went back. Is this correct or just the rambling of a mad man who reads too much sci Fi? Also yes the name of the drive would be the pop drive, do not steal.
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Jun 26, 2021 14:18
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Inspector 34 posted:I don't think I understand this well enough to describe a situation like that. I'm just trying to understand it conceptually at all. But I'll try. The bolded part isn't true even in traditional Newtonian physics. Kinetic energy is 1/2mv2. The sum of the energy of two balls at 20 is much less than one ball at 40.
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Jun 26, 2021 14:26
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Son of Rodney posted:Yeah relativistic and imaginary ftl travel is amazingly mind bending, and I just thought of something maybe someone smart can confirm/deny for me Yes. By 'popping' back to earth you have escaped your own light-cone and broken causality.
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Jun 26, 2021 14:41
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If causality can't stand up to even slight stress then I don't want anything to do with it
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Jun 26, 2021 14:44
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Blue Footed Booby posted:The bolded part isn't true even in traditional Newtonian physics. Kinetic energy is 1/2mv2. The sum of the energy of two balls at 20 is much less than one ball at 40. Choosing to observe from a point where one ball is at rest doesn't make the other ball strike it with any more energy, though. It just means the whole system you're considering has more energy than if you were looking at it from a different point. When you're doing a collision calculation for one ball at rest and one ball moving, you also have to take the kinetic energy of the entire system into account, because the center of mass of the two balls is moving with respect to your frame of reference. This gives the whole two-body system a non-zero momentum and a non-zero kinetic energy, but this motion through space doesn't grant any extra energy or momentum to the interaction between the two bodies. The extra energy of the one ball moving at 40 vs the sum of the two balls moving at 20 mathematically accounts for the system's kinetic energy. If you do the math for the collision from the center of mass of the two bodies - this is the both balls moving at 20 case - it cancels out that system energy and ends up making the math a little simpler. In both cases, momentum is conserved, and the change in momentum felt by each ball when they collide when both are moving at 20 is identical to the change in momentum if one was at 40 and one was at rest.
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Jun 26, 2021 16:23
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https://www.iltalehti.fi/kotimaa/a/a4a92d80-1030-4dbc-9202-b17f1a84b639 (in moon language, use translator) Three ~20 year old youngsters on the Midsummer's Eve night notice that the dry lightning storm just set the entire roof of an apartment building ablaze in the the middle of the night, alert the fire brigade, and rush into the building to wake and alert the people living there. They arrive on the scene 5 minutes before the fire brigade, and start the evacuation; as a result 0 casualties even if the building has several elderly people who have trouble using the staircase. When fire brigade gets things under control, the entire apartment building is left unlivable and 4 topmost floors are basically burned to crisp; the lightning rod had failed. Der Kyhe has a new favorite as of 19:26 on Jun 26, 2021 |
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Jun 26, 2021 19:24
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Der Kyhe posted:https://www.iltalehti.fi/kotimaa/a/a4a92d80-1030-4dbc-9202-b17f1a84b639 (in moon language, use translator) The occurrence is not only truthful, but also very remarkable. It is left to those knowledgeable of nature to judge further. (that is super badass)
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Jun 26, 2021 19:29
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Carthag Tuek posted:The occurrence is not only truthful, but also very remarkable. It is left to those knowledgeable of nature to judge further. In case if you are wondering if this is shitposting by Iltalehti, which is a tabloid, YLE (the BBC of Finland) https://yle.fi/uutiset/3-11998480 also confirms this story. (still in moon language)
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Jun 26, 2021 20:50
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no i just thought it was an appropriate quote (from here)
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Jun 26, 2021 20:56
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Son of Rodney posted:Yeah relativistic and imaginary ftl travel is amazingly mind bending, and I just thought of something maybe someone smart can confirm/deny for me This is all correct, but none of it has much to do with time travel/causality violation. You can see yourself because of the light travel time. Seeing yourself in your past isn't special - you do that every time you look in a mirror. When we say that FTL violates causality, we're talking about something much more fundamental than that - it's a result of the warping of spacetime because of different reference frames going at different speeds. Let's say that you FTL instant-jump to 10 light years away. But before you jump back, you engage your non-FTL engines and travel away from Earth at 0.6c. Now, from your perspective, Earth is moving away from you at 0.6c. Because space and time are relative, the moment you left Earth is now 12.5 light years away and 7.5 years in your new "future." Barring FTL, there's still no way to get there or even send a signal there. But since you have an instant FTL drive you teleport back to Earth (which is 8 light years away from you in your new "present"), and use your non-FTL drive to match Earth's speed and land. This speed change also shifts space and time for you, and now the moment where you left is now 6 years in your future. Your trip has landed you six years in the past, and you are free to go shake the hand of your past self and steal their FTL drive and create paradoxes and all the other time travelly things that you might do. If you change the velocity to something other than 0.6c away, and/or change the distance you FTL-jump, you can fine-tune your time travel to go to literally any time in Earth's past or future history, with the only limitations being your engines' ability to get you to that velocity and your FTL drive's ability to teleport that distance.
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Jun 26, 2021 21:07
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Carthag Tuek posted:no i just thought it was an appropriate quote (from here) Yeah yeah, no bad, I get *you*, but in case someone else wonders. Not all of us are mand med uendelige kulturelle citater. This used to be an international forum before going dead and gay, you know. EDIT: And apparently, aggressively Nordic. Der Kyhe has a new favorite as of 21:12 on Jun 26, 2021 |
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Jun 26, 2021 21:07
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Mustachioed flying rodents know more about acoustics than you do
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Jun 26, 2021 23:01
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DontMockMySmock posted:Because space and time are relative, the moment you left Earth is now 12.5 light years away and 7.5 years in your new "future." I follow everything else in your post but I'm not sure I'll ever really grok how the second part of this follows from the first I appreciate all the effort posting itt though
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Jun 27, 2021 02:12
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The Bloop posted:I follow everything else in your post but I'm not sure I'll ever really grok how the second part of this follows from the first Well i didn't post the details of the math. If you have a basic competence with the easy parts of algebra, it's pretty understandable tho. So, in the scenario I posted, the event of leaving Earth is 10 light years away, and at time zero (i.e. the present). The Lorentz transformation, simplified for only one relevant dimension of space, looks like this: γ = 1/sqrt(1-v2/c2) (this parameter is just called "gamma" and I'm only bothering to define it here to make the next two equations simpler) xnew = γ (xold - v*told) tnew = γ (told - v*xold/c2) Plugging in xold = 10 c*yr and told=0 for the old coordinates of the event, and v = -0.6c (negative 'cause moving away) for the relative velocity of the new frame of reference, you get γ=1.25, xnew = 12.5 c*yr, and tnew = 7.5 yr. So those are the coordinates of that event in this new frame of reference. Basically, what the "present" is, to you, depends on how you are moving. So if you can travel places "instantaneously", i.e. to another point in the "present," then when those places are depends on how you're moving, too. (To be clear, you don't have to actually travel instantaneously to break causality, only greater than c, but the math is simpler.) edit: man i forgot how shittily the forums' default font renders lower-case gamma. looks like a weird small capital Y. It's probably normal enough to a greek speaker but it looks really weird to me. edit2: forgot a factor of c in the equation because i'm too used to using "natural units" aka being too lazy to write out the "c" DontMockMySmock has a new favorite as of 02:35 on Jun 27, 2021 |
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Jun 27, 2021 02:31
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What the gently caress is going on in this thread
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Jun 27, 2021 02:54
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Physics is badass.
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Jun 27, 2021 03:00
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I still appreciate the effort but for most people, and speaking for myself specifically, a paragraph of algebra is the opposite of "grokking" something I can follow the math but I can't intuit anything about it, it feels extremely wrong I don't really have issue with most outside-the-normal-frame stuff like huge distances and tiny quantum poo poo but the back in time component of >c travel just feels like we must've got the math wrong, if that makes sense Not saying we did, or that I disbelieve it, just that I only know it by rote not by any sort of deep understanding
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Jun 27, 2021 03:12
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DontMockMySmock posted:edit: man i forgot how shittily the forums' default font renders lower-case gamma. looks like a weird small capital Y. It's probably normal enough to a greek speaker but it looks really weird to me. 𝛾
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Jun 27, 2021 03:51
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ain't gonna remember that code, nor bother looking it up, next time I do a SR math post The Bloop posted:I still appreciate the effort but for most people, and speaking for myself specifically, a paragraph of algebra is the opposite of "grokking" something It feeling "wrong" is normal. The thing about humans is that we're hard-wired and well-trained to deal with the world of things between the sizes of 1mm and 1km, going at speeds no higher than that of a thrown rock. All this stuff sounds crazy to us because it is crazy, and we only believe it's true because it fits together into a system of rules built on sound logic, and has incontrovertible observational evidence. When you venture outside of that range we're comfortable with, our intuition just isn't helpful, and you really just need to crunch numbers until you sort of build up a new intuition. I posted the math because, well, that's what I got. Graphing also helps but I've been too lazy to do that other than to post those Desmos links.
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Jun 27, 2021 04:59
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ultrafilter posted:Physics is badass. What is that, please ?
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Jun 27, 2021 06:01
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The Bloop posted:I don't really have issue with most outside-the-normal-frame stuff like huge distances and tiny quantum poo poo but the back in time component of >c travel just feels like we must've got the math wrong, if that makes sense It's why the pithy version is "Relativity, causality, FTL, pick two". If relativity is correct, and you have a way to do FTL, you can theoretically set up a situation where effects precede causes. So either relativity is wrong (but it's been very good at predicting behavior so far & we don't have any better model), FTL is impossible, or time travel is possible Lady Disdain posted:What is that, please ?
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Jun 27, 2021 06:10
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It's why Dr. Manhattan is blue in the Watchmen. 
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Jun 27, 2021 06:20
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Der Kyhe posted:Yeah yeah, no bad, I get *you*, but in case someone else wonders. Not all of us are mand med uendelige kulturelle citater. This used to be an international forum before going dead and gay, you know. vi spiller den samme bold
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Jun 27, 2021 06:28
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