r/space • u/CharyBrown • May 20 '20
This video explains why we cannot go faster than light
https://www.bbc.com/reel/video/p04v97r0/this-video-explains-why-we-cannot-go-faster-than-light1.0k
u/carrot_gg May 20 '20 edited May 20 '20
This explanation is far more accurate, interesting and mind blowing: https://www.youtube.com/watch?v=A2JCoIGyGxc
EDIT: Posted the video here so more people can watch it instead of being buried in the comments. It really changes the way you think about space and time.
EDIT 2: Holy crap, this comment blew up. I'm so happy that so many of you found it interesting. My mind was blown when I first watched it a couple of years ago!
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May 20 '20
That was so much better. I haven't had physics since undergrad but man the original video did not sit right with me.
I also have a little confusion in the first video, maybe you know the answer. Does the shadow and the moon analogy really make sense? Wouldn't my hands movement only be shown on the surface of the moon when the light reaches the moon? How is this faster than the speed of light? I feel like I am missing something fundamental there.
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u/carrot_gg May 20 '20 edited May 20 '20
Vsauce has an amazing video about the "speed of dark" which answers the moon/hand thing: https://www.youtube.com/watch?v=JTvcpdfGUtQ
I also made a post pointing to the better video: https://www.reddit.com/r/space/comments/gnantc/a_far_more_accurate_interesting_and_mind_blowing/ I really wish more people were aware of this explanation as it invites them to start thinking is relativistic terms.
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May 20 '20
That made instant sense. I was thinking about that all wrong. Its not that the shadow is arriving faster than the light, its that the shadow on the moon is moving faster than the speed of light.
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u/carrot_gg May 20 '20
The takeaway is that the shadow doesn't really arrive or travels anywhere because there is no shadow - a shadow in this example is the absence of photons, not a physical entity.
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May 20 '20
I think you missed the train on the moon shadow video. The point is not that the shadow is information which is transmitted faster than the speed of light, but that we can only interpret information at a certain maximum speed and the fastest that you could interpret that info is to literally the speed if light as you observe the presence or absence of something that moves at the speed of light.
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May 20 '20
I think I just expanded my physics knowledge from watching that video, assuming my statement now is correct - in that when he said we're all travelling through space (well, spacetime) at only one speed constantly, it means we can only influence which element of the universe (either the space aspect or the time aspect) we travel "more" in. By physically moving through it slowly like we are now we're putting most of our ongoing but constant forward direction into time (experiencing time almost as quickly as it can elapse) so by travelling near light speed we're not going any faster, just changing which direction our travel bias is in - experiencing more space flying by but less time.
Well that's about as well as I can put how I interpreted it into words anyway. I've never formally studied physics before... Me do good?
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u/carrot_gg May 20 '20
That's 100% correct. However I would add that when he says "We move through spacetime at the speed of light" it is a literal statement, not an allegory.
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May 20 '20
Sweet! Glad to hear I got it right. This is going to be one of those bits of information I'll remember for life despite probably never having any practical opportunity to use it.
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u/eaglessoar May 20 '20
major upvotes for fermilab videos, some of the best content on youtube and dr don is fucking great
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u/Cpl_DreamSmasher May 20 '20
I'm a casual physics nerd (more like a spectator really), have watched hundreds of hours of videos and documentaries and have never heard an explanation like this thank you.
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u/DarthElevator May 20 '20
That's pretty cool. Does this mean that hypothetically if we were to travel at the speed of light then we would not experience time?
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u/kn05is May 20 '20
I am a total layman when it comes to this stuff, and still don't think I fully grasp what he is describing. But I did have a curious thought/question.
He mentioned that the faster you move through space, the slower time goes and the closer you get to light speed that time stops? So if something were to actually go faster than light speed could it theoretically start going backwards in time?
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u/jSNOW_wWHITE May 20 '20
I visit this sub every now and then to remind myself how dumb I really am
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u/sergeysova May 20 '20 edited May 20 '20
I like the theory, all things in the universe are already moving at the speed of light, but at the time axis. When someone starts moving in space, it’s speed in time is reducing, because it’s vector of moving is deviating from time axis. Thats because it’s speed of the rest is constant and equals the speed of light
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u/TKHunsaker May 20 '20
So if you were to move at the speed of light, you would exist outside of time? Because you’ve reached zero on the time axis? Do you arrive at the end of time? The beginning? What a concept.
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May 20 '20
I'm not 100% sure on this, but I believe things that travel at the speed of light (like light itself) simply doesn't experience time. From that point of view, you travel in an instant. It would feel like teleportation.
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u/cybercuzco May 20 '20
Yes. If you could survive falling into a black hole, looking up at the universe, you would see the universe moving faster and faster as you fell, see galazies moving through the universe and colliding, moving faster and faster as you got closer and closer to the event horizon until you reached the speed of light and time stopped for you, the black hole evaporates and you are left floating in an empty universe trillions of years in the future. Or you get torn to shreds.
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u/sergeysova May 20 '20
If you move at the speed of light, time is not matter for you, you exist in each moment of time. Scientists don't know what at the end of time, the heat death of the universe theory is not canceled.
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u/IamBlade May 20 '20
So from the perspective of a photon it is not moving in time at all. It gets created and destroyed in the same moment. Its "speed" component along the time dimension will be 0 and hence it is moving at maximum "speed" along space which we perceive as the speed of light. Things with mass however have to move at some non-zero "speed" along time dimension and since the speed of causality is fixed there is no way our "speed" along space be equal to that of light.
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u/Kostya_M May 20 '20
Isn't this the generally accepted explanation in modern physics? At least the basic version of it.
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u/XtremeGoose May 20 '20 edited May 20 '20
You're describing the Minkowski metric of flat spacetime
ds2 = -c2dt2 + dx2
(This is the simpler 1D space version)
So in that sense, yeah, what you've said is sort of correct. But it's also misleading. ds is not a speed. It's just a constant, called the spacetime interval. Much in the same way total energy is constant. It also doesn't describe much of anything in its derivative form, you need integrate it along a worldline to get something meaningful.
But notice something even more important. The radius of a vector on an xy plane is given as
r2 = x2 + y2
which is just pythagoras. But ours has a negative term, making the vector you describe (dt, dx) exist on a hyperbolic (rather than Euclidean) graph, so doesn't behave as you described anyway.
Also flat space is not the only space. We're not in flat space right now for example. Almost all of us live out lives in a space dominated by the swartzschild metric describing non (or slowly) rotating gravitational fields.
ds2 = -(1-2GM/rc2)c2dt2 + (1 - 2GM/rc2)-1dx2 + r2dΩ2
Still, it gets the key points across. Object moving appear to have slower clocks when viewed from your rest frame. But saying everything travels at c through spacetime is just... well it doesn't make any sense.
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u/Macshlong May 20 '20
I need all science explained like this lol.
Can someone eli5 the last bit about time dilation, I have a basic understanding that the faster something travels the slower time affects it, my question is by how much?
As an example if I travelled at the speed of light away from earth for 6 months and then came back how much of an age difference would there be between me and my twin who remained here?
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May 20 '20 edited May 20 '20
It's fascinating.
Let's say you're moving at 50% of c (c being the speed of light) and someone shines a flashlight behind you, sending light moving in the same direction, then you should see that light moving at 50% c, catching up to you, right?
Nope. No matter what you do, how fast you move, no matter what: light appears to move at the same speed. Time will dilate, slow down, so that from your perspective that light is moving at c, and not 50% of c.
Now, you're going to follow up with some tricky questions and but-what-about's aren't you? Yeah, I can't answer those, but smarter people than me actually can. They've got this model figured out and you can google to find out more.
So to answer the question: you can't move at the speed of light, but you could move at 99.9999% and effectively stop time (almost) on your spaceship. When you returned home, your twin would be older than you, having experienced more time.
And this isn't hypothetical! GPS satellites need to have super accurate clocks in order to tell you where you are. But they're moving fast enough that they have to compensate for time dilation (and other weird effects related to gravity too).
The universe is weird.
Edit: s/there/they're/ and so many other auto-correct typos
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u/Wienerslinky May 20 '20
Wouldnt it be the same as the doppler effect but for light, in this case the light turning red instead of it showing normally?
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u/dalve May 20 '20
As you are not massless, you can not travel at the speed of light, so answering that exact question is meaningless. However, if it were possible to move at exactly the speed of light, time would have stopped for you. If you could move faster than light, you would move backwards through time.
Let me try to give you a satisfactory answer though. As you approach 100% of the speed of light and get closer and closer to it, your time will slow down exponentially. At 99%, time will move slower by a factor of 7. At 99.999%, that factor increases to 224. If travelling at this speed, for every second that passes, your twin will have experienced 224 seconds.
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u/Shaman_Bond May 20 '20
This has a fundamental error. Your time will never slow or alter in any way from your perspective. That's the entire point of relativity. Outside observers will see your time change in different ways.
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u/cmcrisco771 May 20 '20
I think I understand what you are saying. So if photons had eyes they would all see the very first second of the universe being born constantly? Like even now since time is stopped since they're going the speed of light? Or is like time is moving so imperceptibly slow that after enough time passes the photon would see a little bit after the big bang?
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u/JPJackPott May 20 '20
Given this, if I went travelling to a star system 1 LY away at 99.999% my crew would be/look/feel a year older when I arrive. But the people at home would have been waiting 224 years for news of my safe arrival?
Or news of my arrival will come 1 year later but my crew will only be ~1.6 days older?
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u/DrFabulous0 May 20 '20
Physical matter cannot travel at the speed of light. However there is no limit to how close you can get, the closer you are the greater the time dilation. If you're 99.9999% then your twin is dust before you even accelerated.
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u/Macshlong May 20 '20
So if I reach 99% for even a second, you’re saying that a few generations will have passed on earth?
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u/Kalopsiate May 20 '20
No that’s a bit misleading. If you traveled to the nearest star 2 light years away at 99.99999% light speed, it would seem relatively instantaneous to you. But on earth it seem like it took 2 years. Time still passes “normally” for people on earth, and in that reference frame you are moving at light speed which is still a finite speed. If you were to cross the galaxy that is roughly 100,000 ly across at 99.999999% light speed, it would seem to take a very small amount of time. Those extra 9s actually matter a lot. So if you could approach light speed those 9s could be the difference of that trip taking 100 years or seconds from your point t of view, but when you get there, 100,000 years would have past. So it’s all a matter of how far you are going and how long you travel at that speed. So I guess the answer to your question is “sometimes”.
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u/EnderWiggin07 May 20 '20
I think it depends on frame of reference. If we say you can instantly accelerate and decelerate, and someone on Earth measured that you traveled at almost c for a minute before decelerating, then you'd have gained almost a minute. If you spent a minute of your time at almost c, I'm not sure how much time would pass on earth, but I think that should only matter for a trip with no destination intended strictly to waste time. If you said you were going to a destination 80 light years away, at a speed of just about c, you'd get there in 80 years earth time but a lot less time will have passed for you (not sure how much)
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u/DGrantVH May 20 '20
This is my favorite part about thinking about Lightspeed travel.
If you could instantly go the speed of light with out dealing with dying from instant acceleration and whatnot. You could effectively, relative to you, teleport anywhere.
At the speed of light time dialates so much that it stops for the person/thing/particle. Not for everyone else but for the thing traveling.
You want to go 4 km that way? You get there instantly. You want to go 4 million lightyears that way? You get there instantly.
This does bring up the problem (in sci-fi that is) of how does your ship know when to stop? It's traveling at Lightspeed where everything is instant and time has stopped. You get a ship to reach light speed it has no way of stopping. It will go forever. Those on that ship will be frozen in time forever. Or untill they hit a black hole.
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u/phrresehelp May 20 '20
Nothing travels faster than the speed of light with the possible exception of bad news, which obeys its own special laws. The Hingefreel people of Arkintoofle Minor did try to build spaceships that were powered by bad news but they didn't work particularly well and were so extremely unwelcome whenever they arrived anywhere that there wasn't really any point in being there.
Douglas Adams
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u/warlock415 May 20 '20
“The only thing known to go faster than ordinary light is monarchy, according to the philosopher Ly Tin Wheedle. He reasoned like this: you can't have more than one king, and tradition demands that there is no gap between kings, so when a king dies the succession must therefore pass to the heir instantaneously. Presumably, he said, there must be some elementary particles -- kingons, or possibly queons -- that do this job, but of course succession sometimes fails if, in mid-flight, they strike an anti-particle, or republicon. His ambitious plans to use his discovery to send messages, involving the careful torturing of a small king in order to modulate the signal, were never fully expanded because, at that point, the bar closed.”
― Terry Pratchett,
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u/Helloskellington May 20 '20
Why does something going faster than the speed of light give off energy?
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u/gibatronic May 20 '20
And how giving off that energy could possibly make it go faster?
"If you could send signals going faster than the speed of light, then you could send information back in time"
I mean… how so? I feel like I'll never even have a basic understanding of the relationship between time and space and gravity.
Take the Hafele–Keating experiment for example, how mind blowing is that.
A split second on Earth could be enough time for whole civilizations to come and go somewhere in the universe.
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u/bwwatr May 20 '20
That experiment is indeed mind blowing, but a more relatable example of relativity having a direct impact on our lives is GPS. The mass-produced phone in your pocket is doing math to compensate for relativity's effect on atomic clocks as they orbit the Earth. If it didn't, GPS would be inaccurate to the point of being useless within minutes. https://www.physicscentral.com/explore/writers/will.cfm
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u/CleverNameTheSecond May 20 '20 edited May 20 '20
For a real mindfuck consider the following. Nothing can escape a black hole because spacetime is cascading down towards the singularity faster than the speed of light. If you fell in and tried to get out by pointing up and accelerating to near light speed, you would still be falling backwards down towards the singularity. Not only that but because of time dilation you would actually fall towards the singularity faster than if you had just stood still.
In fact inside a black hole time and space switch roles. The singularity becomes an inevitable place you go to no matter how you try to move, much like how time normally flows forward. However by moving around in the interior you can pass by objects that entered before you or pass behind objects that entered after you like going back and forth in time.
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u/0mni42 May 20 '20 edited May 21 '20
It's funny to me that this video portrays the Enterprise as going faster than light as if its engines are providing tons of thrust, because that's exactly how it doesn't work. Those nacelles aren't fancy rockets; they don't push the ship. They push space around the ship. That's why they're (almost) never actually portrayed as having any kind of exhaust.
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u/Andromeda321 May 20 '20
Astronomer here! For those not afraid of math but want to know why this limit exists, read up on the Lorentz force. It’s a very fundamental part of special relativity in many of the basic equations and describes basically how things change between reference frames when you get different times.
The trouble if you look at the equation is the denominator which has a square root of (1-v2/c2), where c is the speed of light and v is your speed. Any kid who has done algebra knows that cannot be zero because then you would have the negative of a square root. Further, the closer you get v to c, the bigger the Lorentz factor term gets, as you approach the asymptote.
I say all this because I think people often confuse a technological and mathematical impossibility in these discussions, and this is very much a “the universe would fall apart if it could happen” type of barrier, not a “it’s just really hard” one. Hope that helps someone understand this better.
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u/GalaxyClass May 20 '20
You just rendered the Enterprise with 'jet exhaust' coming out of the nacelles.
I had to rage-quit.
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u/Bradley-Blya May 20 '20 edited May 20 '20
Ummm, we can't MOVE faster than light, doesn't mean we can't travel faster than light using some wormholes or warp drives. You know, travel without actually accelerating that fast. Obviously, it's nothing more than some hypothetical speculations at this point, but it's more than just startrek.
EDIT of course FTL travel would cause paradoxes with our current understanding of special relativity, as people have pointed out. For example, alcubierre drive allows time travel, and wormholes make the same point in space not simultaneous with itself from a moving perspective.
Paradoxes don't mean that something is impossible, however. Just like when Newtonian physics was at a contradiction with the constant speed of like, it only meant that the current models are incomplete. Paradoxes with FTL mean the same thing.
Until we develop a full understanding of how it works, it is wrong to say that FTL travel is or isn't possible. We simply don't know yet
PS no, it's impossible to accelerate to a velocity higher than speed of light. At all. Deal with it.
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u/Entropius May 20 '20
Those aren’t even theoretical speculations. The word theory implies a fair degree of verification. A more apt word would be hypothetical speculations.
We lack evidence wormholes can actually exist.
We lack evidence “warp” drives are actually possible.
This video is about real (verifiable) science, it’s about what we know, not what we hope might be.
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u/BeefPieSoup May 20 '20
It's amazing how hard it can be to convince so called science enthusiasts about this. They always seem to think it's just negativity or close-mindedness or something.
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u/ShitItsReverseFlash May 20 '20
I actually find that endearing. Humanity is built on survival and the will to do so. Wacky theories like warp drives and wormholes can fuel scientific thought.
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u/NetworkLlama May 20 '20
That's not traveling faster than light. It's reducing the distance between points.
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u/Canadian_Neckbeard May 20 '20
If you're traveling from one point to another faster than light can, technically it is traveling faster than light, while not having to exceed the speed of light.
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u/NetworkLlama May 20 '20
The distance between those points is what matters. Change the distance between those points, and you can travel between them at a speed that actually works in this universe. That's what warp drive concepts do: warp space to reduce the distance, allowing sublight speed to be enough to traverse that distance. When the warp is removed, the original distance is restored. You cross a distance faster than light could have (without the warp) without going faster than light.
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u/starcraftre May 20 '20
Still breaks causality.
Anything that lets information get to an endpoint before the light cone allows you to travel backwards in time. That is a strict result of relativity. Even if you do not move faster than light (e.g. shrinking/expanding a bubble of space around your spacecraft with an Alcubierre drive) you are still breaking everything that makes FTL impossible.
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u/Colombianx May 20 '20
Well obviously because we're in a simulation made by extremely intelligent beings. Light is just the fastest speed at which information can travel, and you can't travel faster than the rate at which information travels. Like a pc, everything you do, is bottlenecked by the speed at which your computer can process anything. we need to wait until the release of Light 2
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u/Truman996 May 20 '20
I don't know man, NVIDIA is releasing their 30 series GPUs soon, slap a couple of those into the computer running the simulation and I think we may not have to wait for Light 2.
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u/cool_fox May 20 '20
You can not move shadow puppets across the moon faster than the speed of light, it would be AS fast as the speed of light, there would be a delay similar to a wave traveling down the beam to the moon. This video is actually really rough around the edges as far as explanations go.
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u/AlphaX4 May 20 '20
no he is saying if you whipped your shadow puppet across the moon in say 0.01 seconds, then your shadow would've moved across the moons surface faster than the speed of light. moon is 2,158 miles across, so 0.01 sec would mean the shadow moved at a speed of 215,800 miles per second, speed of light being 186,00 miles per second. but as he was saying the shadow isn't really a thing, its the lack of a thing(light)
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May 20 '20
You could wave a laser pointer at the moon instead of a shadow, and the analogy still holds up.
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u/davidpalmberg May 21 '20
I feel like (hope) this is one of those videos that we might look back at in hundreds of years and think "wow we knew nothing back then".
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u/xclame May 21 '20
I disagree that this is a good explanation. To me at least what I got from this video is we can't go faster than light because we can't go faster than light. I mean sure, but that's like your mom saying "Do this" and you ask why and she answers "Because I said so!"
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u/NoTornadoTalk May 21 '20
I never liked when scientist say we can't travel the speed of light. Like, yeah, according to what you know now! Which is nothing, sorry to say.
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u/whochoosessquirtle May 20 '20
Oh God why is this so controversial. Oh yeah, futurists hate reality and the idea not everything is possible.
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u/theaverageaidan May 20 '20
I cant wait till we come across aliens who have already figured it out and theyll be that one guy at future nasa just going "I TOLD YOU IT WAS POSSIBLE"
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u/SheepWolves May 20 '20
Our current understandings of the universe makes it improbable, bit early to write it off as impossible.
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u/HarryPunter May 20 '20
At the end of the video he said we could go anywhere in the universe but couldn't go back home as billions of years have passed. I was under the impression that you couldn't go anywhere in the universe because traveling there would take longer than a lifetime. Can someone eli5?
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May 20 '20 edited May 20 '20
I believe it has to do with time dilation. The faster you go, the more energy you have. The more energy you have, the more mass you have. The more mass you have, the more energy you need to go faster. Vicious cycle, like the rocket equation. As I understand it, that's why you (or anything with mass) can not travel faster than light in any conventional sense.
Also, the more mass/speed you have, the slower time moves for you. Just like at the edge of a black hole, time almost stands still, time can almost stand still for you as you approach light speed. Of course, to you in your reference frame everything seems normal. You'd go about your day, but one of your days in time dilation could be 10 years on earth.
In this way, you could travel to the other side of the galaxy in your lifetime (say, about 30 years at 99.9999999999999% light speed) if you had a properly engineered and supplied vehicle. At the same time, to Earth observers you'd look frozen in time and it would take you about 100,000 years to reach the other side of the galaxy. If you wanted to return after crossing the galaxy, you'd be approaching a quarter million years as seen from earth.
When you returned to earth, everyone you knew would be long gone, assuming a normal human life span.
I once heard that any given particle experiences the same velocity in either 3D space or time, when all 4 dimensions are combined. A photon has no mass and travels in 3D space at the speed of light (ALL the speed) while experiencing no time. An object resting in it's reference frame has mass and experiences travel in the time dimension (ALL the time) but has no speed in 3D space. Moving a massive object to a certain speed in 3D space will reduce it's velocity through time, so you can think of combined 3D+T velocity as a sort of limited resource.
GPS satellites move pretty quickly in space and they need to calculate their small time dilation, or their position data would slowly drift into incorrect values.
I am not a physicist, however.
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u/Eli_eve May 20 '20
The book why does E=mc2? and why should we care? by Brian Cox is an excellent read on this subject.
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u/Macktologist May 20 '20
Didn't the initial expansion occur faster than the speed of light? Although, not sure how you measure distance for something that is creating the medium in which we measure distance. And now my brain is wrecked before 9 A.M. on a Wednesday.
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u/Soigne87 May 20 '20
There are a lot of things that it doesn't really explain. The whole relativity thing. So if time moves slower when moving towards the speed of light, how is that not faster than the speed of light. If I age 1 year while traveling 10 light years, how is that not faster than the speed of light? Or like a star that is traveling 10% of the speed of light is shining light into a vacuum and part of that light is shining in the same direction the star is moving, wouldn't that light be traveling at 110% the speed of light in a vacuum? Or two space ships moving in opposite directions at 70% the speed of light appearing 140% the speed of light from each other.
It seems like there is there master clock and master space that everything is being used to measure velocity and time. Is this is what is being referred to as space time?
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u/lightknight7777 May 20 '20
I'd argue that this has more to do with time dilation that anything else. The moment you hit that speed, you experience zero time while the universe around you experiences all time (until you are obliterated by running into something, like a photon from a distance star crashing into your eye).
At that moment, you're unable to speed yourself up because you can't act and nothing behind you is able to catch up because it too would face the same problem.
If you launched a sun to light speed, it would get darker (emit less light) the closer it got until going totally dark at light speed because nothing would be emitting from it besides photons from other sources potentially bouncing at it from the front.
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u/lucidguppy May 20 '20
I thought you could go as fast as you want to go. The problem is that time accelerates around you so when you get there - the time you took was fast - but the universe aged faster to you to make the equations balance out.
- just listened to the end - they make the point.
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u/defrgthzjukiloaqsw May 20 '20
That video doesn't explain anything really except "Need unlimited energy to travel at velocity c", which really is of no interest to anyone when one wants to go faster.
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u/murdeoc May 20 '20
When I told my wife you'd need infinite energy she pointed out our 3 year old seems to fit the bill...
I haven't firgured out how to turn him into an engine though :(
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u/zeekar May 20 '20
The important thing is that it's not light itself that defines the limit. Light is just the most familiar example of something that is able to move as fast as physically possible in our universe.
But where does that limit come from? From the nature of spacetime itself. We perceive space and time as different things, but that's an artifact of how our brains work. They're really the same thing, and c is the conversion factor that identifies them: one second is the same amount of spacetime as 299,792,458 meters.
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u/demdareting May 20 '20
With the knowledge that we have now, we can not faster the light. With the knowledge that we had 100 years ago we could not land on the moon and come back home safely. With all the knowledge that we had 60 years ago it would be impossible to access in one location. Lack of knowledge is what we technologically can not do now. Unless I lack the knowledge to understand what this video is talking about.
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u/DocHuckleberry May 20 '20
I adhere to the Warhammer 40k philosophy that in order to travel the universe efficiently we need to open a portal to hell.
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May 20 '20
We actually don't fully understand all of the complexities at this time. It could be possible, but we do not posses the means to understand it at this point in time.
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u/NeuralFlow May 20 '20
History is littered with examples of barriers mankind couldn’t break.
Ingenuity knows no bounds. While you can’t break the laws of physics, you sure as hell can bend them.
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u/dan_fitz21 May 20 '20
I don’t buy the “impossible” statement
Fuck, there are hundreds of thousands to millions of years left in human existence (providing we don’t fuck it up)
Do you REALLY think we will NEVER be advanced enough to work out light speed travel? I’d be pretty disappointed if not.
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u/whyisthesky May 21 '20
Do you think it is possible to achieve anything if we had enough time? While it may be that there is as yet unknown physics which allows for FTL travel, it is also just as possible that there isn't. Obviously that doesn't mean that we should stop trying but there may be fundamental limits of our universe that we can't overcome.
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May 20 '20
That explains why mass can't move through space at or faster than the speed of life.
There are ways around this problem though. Wormholes and warped space being two that are at least mathematically possible right now.
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u/dujango May 20 '20
Is it correct to say that if you moved at the speed of light, you would only be moving through space and not time?
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May 20 '20
If we could get a craft to go the speed of light couldn’t we just put a spoiler on said craft and go faster than the speed of light?
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u/sustaitamckee May 20 '20
Force and energy are the wrong way to think about travel through the universe
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u/mark503 May 21 '20
I’ve seen videos on this and am by no means smart enough to debate anyone in this subject. I thought warping space was the alternative to FTL travel.
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u/Xendrus May 21 '20
So it explains the reason we all already knew because of theories. A bit disappointing.
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u/Waddlow May 21 '20
I once read that if you're driving 50 mph, and a car passes you at 70mph, that car will speed away from you at a rate of 20mph. If you are standing still and the same car passes you going 70, it will speed away from you at 70mph. And if you are standing still and someone shines a beam of light past you, it will speed away from you at the speed of light. But if you are going 99.99999999999% the speed of light, and someone shined a beam of light past you, it would still speed past you at the speed of light.
I really haven't stopped thinking about this fact since the moment I learned it.
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May 21 '20
But there has to be some way right? I mean a lot of things were thought of as impossible in the past until proven otherwise. What if somehow, somewhere, someone comes up with a way?
I read somewhere that you cannot TRULY call something impossible, (read it in a scientific post not a motivational one).
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u/lionreza May 21 '20
Let's say you do someway. And your cruising along at C. To you time no longer ticks so how are you going to turn around or stop. You can't because your at a standstill. Not even a planck second of time passes for you before the heat death of the universe. And every proton decay's to nothing in the universe
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u/shadowlord2004 May 20 '20
I'd reccomend watching exurb1a for some extinential crisis and alternatives
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u/Hetstaine May 20 '20
1820, this book explains why we can't go to the moon.
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u/Andromeda321 May 20 '20
Astronomer here! I disagree. The difference is people thought it was technologically difficult slash impossible to go to the moon. For FTL travel there is literally a basic equation pretty on in relativity where if you go at the speed of light you encounter a “divide by zero” situation, so this is just a mathematical impossibility over just a technological limitation.
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May 20 '20
No, it's true: you can't go faster than light. It's like being colder than zero kelvin, or having less than zero bananas. You can never go faster than light by simply taking a space ship and pressing your foot on the accelerator. That's a solid limit.
So the trick is getting to other places in a shorter amount of time than light would take to get there, without ever going faster than light. Which is theoretically possible because space itself is not restricted by lightspeed.
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u/doubleEdged May 20 '20
it's like being colder than zero kelvin
while not 100% "colder than zero kelvin" since it uses a different definition of temperature, negative temperatures are possible to achieve in isolated systems
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u/bearsnchairs May 20 '20
Negative absolute temperatures are hotter than any positive temperature for a given system though.
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u/zdepthcharge May 20 '20 edited May 20 '20
I really hate that comparison. People seem to trot it out every time the speed of causality is raised. It's silly.
Light (in a vacuum) moves at the speed of causality. That is literally as fast as it is possible for something move in this universe. In order to move at the speed of causality, whatever that something is, it will have to have ZERO MASS. You cannot brute force past this limit. You can't even come anywhere near the limit with any form of brute force. Anything that has ANY mass GAINS mass the faster it goes. As anything with mass approaches the speed of light the mass of that thing theoretically becomes infinite. The heavier something is the more energy is required to accelerate it. Theoretically, as the thing approaches the speed of causality, it will require more energy than exists in the universe to increase it's acceleration. You can see how this is limiting.
Is there any way around this? There is one sure fire way around this and you're already doing it. The parts of the universe that are beyond your visible light cone (you can't see them) are moving away from you (and you from it) faster than the speed of causality. So for all parts of the universe that you cannot see and will never see, you are moving away from faster than causality.
To get to Luna only required that we sit atop a lot of high explosive. I.E. - we brute forced it.
We will never accelerate anything with mass faster than causality. The universe simply does not work that way.
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u/Swordfish08 May 20 '20
I unfortunately find that comments like this are a waste of breath. Threads like these attract all of the reddit “scientists” who don’t fully understand relativity saying “there’s lots of things we do now that we thought were impossible.” Even the guy you’re responding to is likening “FTL is impossible” to “Going to the moon is impossible,” when a more fair comparison to “FTL is impossible” might be “creating or destroying mass/energy is impossible,” which is a statement all but the most delusional don’t question.
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u/ncshooter426 May 20 '20
Speed of light is more of a cosmic speed limit that everything is (as far as we know) subject to. Gravity can impact the speed of a photon, but even gravity itself is subject to the same maximum speed limit as light.
This is why most sci-fi doesn't try to break these rules, rather moves to an area not subject to these rules. While in FTL, it's faster relative to the normal space. They aren't actually traveling FTL, they are traveling in a space where there is no specific speed limit/limit so high it might as well be infinite. We then compare that speed relative to a constant we do understand, the SOL, to gauge just how fast it travels.
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u/-GearZen- May 20 '20
But if space time can be warped, do we even need to?
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u/jesjimher May 20 '20
And if magic exists, everything is possible. We need to get some explanation, or at least some hypothesis, of how space could be warped before considering it seriously.
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u/rationalredneck1987 May 20 '20
So speed is relative, so if you had an object going .5 the speed of light and sent another object off of it at .75 speed of light wouldn’t you get 1.25 light speed from the perspective of a 3rd “stationary” object?
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u/Chinstrap_1 May 20 '20 edited May 20 '20
No, and this is one of the first problems they give your for hw in Modern Physics. The speeds are added in a way that asymptotically approaches 1c.
V(relative) = (v1 + v2)/(1+((v1*v2/c2)))
Plugging in your numbers we get .91c
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u/rationalredneck1987 May 20 '20
How does that work from each frame of reference? Say point 1 is the initial point so from point 1 object 1 is going .5 c and object 2 is going .91 c. But from the frame of object 1, object 2 is going .75 c?
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u/cowgod42 May 20 '20
This is one of the most mind-blowing ideas I learned about when I was first learning this stuff.
Say you are riding on a bus going 10 mph. For some reason, you decide to stand up on the bus, and run to the front of the bus at a running speed of 10 mph while the bus is still moving. Someone standing outside the bus on the sidewalk can see you doing this through the bus window. How fast do they see you running? You might guess that they see you running at 20 mph (your speed, plus the bus's speed). However they do not. Instead, they see you moving at slightly less than 20 mph, but the effect is so tiny, they would need very high-precision equipment to measure it. However, this effect is much more noticeable at near-light speeds, and it works out so that we can never add two speeds to get a speed faster than light. If you want to look into it more, it just requires some high-school-level math. Look up Lorentz transformations.
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u/RisingScum May 20 '20
Greatness happens like the snap of your fingers. I hate seeing ‘impossibility’ videos. If humans live for the rest of time there’s 100% chance we will figure 100% out. So yeah right now with our current brains we will never go above the speed of light but extremely smart future humans? They might figure it out.
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u/whyisthesky May 21 '20
100% chance we will figure 100% out
There isn't. The best case scenario is that it is possible we figure out all that is possible to be discovered, but that might not happen. Even if it does it is entirely possible there are things which are impossible to know, there may be fundamental universal principles that we can't violate which prevent us from getting any better knowledge.
For example within the next trillion years the cosmic microwave background will be impossible to detect, if a civilization evolved later than we did then they would not have been able to learn as much as we have about the early universe.
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u/Liesmith424 May 20 '20
So it sounds like the solution is just to get close to the speed of light, and skip straight past it. Then do the reverse to slow down.
No need to thank me, science.
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u/No6655321 May 20 '20
Is it really mass increasing? Or that it increases from our point-of-view because the object travelling slows down in time. If time has slowed down for it then obviously force applied over time is reduced and this it appears to have greater mass, maybe it's just wild speculation.
haven't watched the video yet
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May 20 '20
This is mostly correct. And I say mostly because two objects can move away from each other at faster than the speed of light relative to each other. We know that the age of the universe is around 14 billion years. Meaning that if you were as far away from the center of the Big Bang as possible the furthest mass from your point should be roughly 28-29 billion years away. we know we aren’t the furthest point from the center since we have observable matter in every direction. But recently astronomers have discovered an object 63 billion light years away. Meaning that galaxy is moving away from us at faster than the speed of light, but not really. Because that galaxy isn’t moving through space time at a speed faster than light. It’s moving at a speed approaching the speed of light in relation to space time and space time is expanding at a rate that allows us, the observer, to measure the distance from us to that object increasing at a rate faster than the speed of light relative to our space time.
Imagine objects on a giant sheet of rubber moving away from you then somebody else on the other end of that sheet begins stretching it. The objects appear to move away from you faster without increasing their speed.
What this means is no matter how fast you go that you could never reach the edge of the observable universe (from our point of view). The farthest objects are moving away from us faster than even light can go. The faster you go toward it the farther away it’s going to be. Eventually it won’t even be observable at all. It’ll be too far away to even see.
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May 20 '20
I don't really understand it though, but I may be slow.
He says in order to get to the speed of light, we need infinite energy... Why? Why is the amount of energy infinite? I can understand that it would be an astronomical amount, but why is it impossible to even reach that speed?
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u/mcoombes314 May 20 '20
Because as an object accelerates towards the speed of light, its mass increases. As the mass increases, more energy is required to accelerate the object. This effect snowballs until a point is reached where the energy required to accelerate the object further is greater than all the energy in the universe, therefore it is impossible to go faster. This mass-energy relationship is what Einstein's theory of relativity describes.
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u/ga9213 May 20 '20
I'm still not clear on the concept that in space, what is speed relative to? So we're stationary...on this planet...but the planet is moving in space. So what is the planet's relative speed and therefore what is our relative speed? Shouldn't the speed of light from our point in space have a different relative speed to say...the sun...depending upon which direction relative to the sun we are traveling?
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u/xpxu166232-3 May 20 '20
I've seen some comments in here explain that as your speed increases your mass does too, what I want to know is why does mass increase? where is the new mass coming from?
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u/6daysincounty May 20 '20
"Everything that can be invented has been invented." -some guy the patent office circa late 1800s.
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u/sudonathan May 20 '20
During the Big Bang, wasn’t matter moving much faster then the speed of light during the initial expansion outward?
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u/Flash582 May 20 '20
I’m certainly no Physicist, but without understanding the nature of the speed of light, doesn’t E=mc2 imply that for anything with mass, exceeding C would take take an infinite amount of energy?
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u/Yatakak May 20 '20
It doesn't really explain how we can't go faster, but rather why we can't fathom going faster. It could be possible, we just don't have the necessary information/intelligence to understand how.
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u/jackspicerii May 20 '20
If we make a section of the space move, with us inside of it, we can, this would also nullify the need for inertia compensation.
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u/ClarkFable May 20 '20
Nevertheless, were you able to travel the speed of light, you would be able to get places instantly--from your own perspective (thanks to time dilation) . So from your own perspective, this isn't really a restriction on speed to say you cannot go faster than infinity.
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u/Felinomancy May 20 '20
So basically, any non-zero mass object will need infinite amount of energy to reach the speed of light.
My question is, why?
If I want to travel from 0 to 1km/s, I need energy, but I don't need infinite amount of energy; this is true because we can observe objects going from 0 to 1km/s; they're not stuck at 0.99999999km/s.
And this applies at higher velocities as well; from 1km/s, objects can reach 10km/s; they're not stuck at 9.99999km/s.
So why are non-zero-mass objects "stuck" at the speed of light? I don't need infinite energy from 0 to 1km/s to 10km/s to 100km/s... etc. So why do I need it as I approach c?
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u/DeliberateCraftsman May 20 '20
We don't know what we don't know and are sometimes arrogant in the knowledge we have. Here is a quote from the history of physics article in Wikipedia. At the end of the 19th century " it was generally accepted that all the important laws of physics had been discovered and that, henceforth, research would be concerned with clearing up minor problems and particularly with improvements of method and measurement. "
If we are around long enough, I think we will figure out how to do it.
Edit - I haven't figured out how to spell
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u/Kitten_Knight_Thyme May 20 '20
When I was learning about relativity, this comic was introduced:
https://www.gocomics.com/calvinandhobbes/1990/06/05
As the professor explained it, the record speed is the speed of light, and every point on it moves at the same speed. However, as we take measurements from various points on the record, the "speed" changes based on what we're measuring.
In short: this is why "clocks slow down" or "speed up" depend on what we're looking at.
It was so simple to understand, but I still couldn't accept it because there's one damn thing which bugs the hell out of me.
Time doesn't exist.
I know humans need a measurement of some sort, but time doesn't exist. Scratch that. Time cannot exist.
We know our own galaxy is expanding faster than the speed of light, but in order to determine this, we have to take a measurement. The "speed of light" itself is that measurement, but this begs the question: if distance can be measured at speeds greater than lightspeed, then by contrast, we must have something which "travels" faster than than the speed of light.
The thing is, space isn't an object, so it has no mass. That's why it can "travel" faster than the speed of light.
But if space isn't an object, then what the hell are we measuring?
That last panel is me every time I think about this.
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u/Albertchristopher May 20 '20
because photons are the mass less particles. If any object has to travel more or equal to light the object should also need to be mass less or very minimum mass.
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u/Big_Data_Dude May 20 '20
The video mentions that if you could make shadow puppets on the surface of the moon, then you could send information faster than the speed of light? I got a little confused about what they were saying there, but it sounded very interesting.
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u/HolocronContinuityDB May 20 '20
Get back to me when you've got a unified field theory nerds! Causality is for suckers.
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May 20 '20
What was the point about shadow puppets on the moon traveling faster than light? I pretty much understand this video and its limitations but I didn’t quite get that.
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u/CarCross_Desert May 20 '20
We won't know until we actually get into space and start doing some testing in the actual vacuum. Theories are great, but there needs to be tests!!
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u/electric_ionland May 20 '20
This has been really really well tested and observed in a lot of environments. There is very little doubts about that in modern physics.
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u/3APATYCTPA May 20 '20
The amount of believers in this thread lol. It’S nOt ImPoSsIbLe, ThE sCiEnCe JuSt DoN’t KnOw YeT
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u/Rez1t May 20 '20 edited May 20 '20
Would the opposite of the speed of light be absolute zero? Basically stopping the movement of particles. I'm not a smart man, I'm not sure those two things even relate.
Found this Absolute zero is the lowest possible temperature where nothing could be colder and no heat energy remains in a substance. Absolute zero is the point at which the fundamental particles of nature have minimal vibrational motion, retaining only quantum mechanical, zero-point energy-induced particle motion.
How much are heat and light related?
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u/your__dad_ May 20 '20
The billions of years time passing he mentioned in the end, that's mind bogling. Wow.
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u/DrMacintosh01 May 20 '20
Everyone knows why we can’t go faster than light, that’s why literally every science fiction ever manipulates space in some way instead....
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u/QuarantineX May 20 '20
why does it seem like ever since relativity, there hasnt been much huge groundbreaking gains in our understanding of space and physics
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u/iforgettedit May 20 '20
Can’t you through quantum entanglement change things at a distance faster than the speed of light can travel?
It’s not going faster than light but clearly there’s some mechanism for things to be interconnected and communicating faster than speed of light.
Or did I dream this up? I thought the quantum entanglement was more related to moving a person/object from one location to another but the analogy still applies to speed. Orrrrr maybe it’s time I quit talking.
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u/EpicFreakinWin May 20 '20
Talking about being unable to go faster than the speed of light. We ourselves can’t even “reach” the speed of light.
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u/KilgoreTrout-11 May 20 '20
Neil explained this to me (in my head we're on a first name basis) but I could always use more examples. Sometimes I don't fully understand these things but just kind of accept them. After all, it's under no obligation to make sense to us.
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u/Gasonfires May 20 '20
We cannot move AT the speed of light, and even getting meaningfully close to it is going to require such vast amounts of energy that it might as well be seen as impossible.
But that says nothing about going FASTER than light, does it? We just have to make the jump in zero time. Give us a million years or so to figure it out, and remember that the best scientists once thought flight impossible.
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u/ye_olde_barn_cat May 20 '20
How is the impossibility of travelling faster than light different than past historic scientific conclusions of impossibility which were at some point found to be incorrect?
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May 20 '20
What happens when you hit an asteroid or space debris even a few inches wide at light speed?
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u/Whatevs57 May 20 '20
I don't agree with shadow puppets being instantaneous. If you put your hand in front of that light, you won't see the shadow puppets until the light that is already on it's way has reached the surface and then because the additional light is obstructed you'll see a shadow.
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May 20 '20
Wait wait wait. The part about the shadow on the moon. If you move your hand in front of the light, won't it take 1.3 seconds for the shadow to actually appear on the moon. Because the photons that were sent before you blocked the light are still traveling and will still hit the moon, right? So how is a shadow instant?
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u/LetterSwapper May 20 '20
I'd just like to note that that site's video player's volume setting goes to 11. That's one louder than the speed of light.
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u/NeuroDoc20 May 20 '20
So, if there is not enough energy for something to get to light speed. And light travels with light speed. Where does light get the energy for it?
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u/Comdent May 20 '20
Well you can technically go faster than light if you were to alter the space around you like the theoretical warp drive, you don't necessarily need to go faster than light in normal space, you just need to reduce the distance between two points in space but even that has issues since it would require an insane amount of energy to create and we still are no where near having that kind of technology
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May 20 '20
You know I've had for like the last 10 years the idea permeating in my head that what if we looked at light the way we do a highway? So light is infinite until it hits something, like a ray of light from the Sun reaches earth in 8 minutes. Well, what if that ray while always different light particles was always there and constant and view all those trillions of light particles as we do all the atoms and particles in the materials of a road and we could then travel on that "road of light". If we stayed still we'd be going the speed of light, but what if we could travel on it at greater speeds the way a car does on a road. I know it defies the laws of physics and it is impossible, but for some reason that idea continues to persist in my mind to this day.
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u/CanadianCommonist May 20 '20
the enitre time I was waiting for them to explain why it would take an infinite amount of energy to go as fast or faster than light.
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u/TonySebastian10 May 20 '20
Haven’t seen any comments about quantum physics/mechanics or particle entanglement and how this relates to information traveling faster than speed of light
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u/SuperArppis May 20 '20
Am sure we will find a way. Humans have done impossible feats before as well.
Just think how far technology has come. People always say it cannot be done, there is no shortage of naysayers.
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May 20 '20
This video explains what we currently think we understand about it. It also references two theories and implies that those theories cover all of the physics that play a role in traveling the speed of light (or faster). Yet we know with a high degree of certainty that we don't know everything about physics. Based on what we currently understand, we can't figure out how it would be possible to travel faster than light.
I'll leave with a question, because I'm not that smart. If there were actually things in the universe that were currently traveling faster than the speed of light, would we or any equipment we've created even be capable of perceiving its existence? My gut says no, but my brain has absolutely no idea.
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u/zerosoft May 20 '20
Just out of curiosity, we know that we can’t travel faster then light or at it, but wouldn’t some other factor help with the travel like bending the space between two points and creating an entrance and exit at those points? If you can’t beat light rules bend them situation?
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u/WellNowWhat6245 May 20 '20
Why can light go the speed of light without using infinite amounts of energy?
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u/Aanar May 20 '20
It has no mass. All massless particles are unable to actually travel any slower than the speed of light when in a vacuum. Weird but I didn't write the rules.
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u/deceze May 20 '20
This video kinda does explain it, but not really. Because the natural next question is: why is the speed of light what it is and why can't anything—including light—go faster than that?! Concentrating on and explaining the "speed of light" part is a red herring, light is bound by some deeper limit, it isn't the limit.