I Think Faster Than Light Travel is Possible. Here's Why.

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Sabine Hossenfelder
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Video Transcript:
I believe there's intelligent life on other planets and the most plausible reason why they haven't contacted us is that we're too boring I mean we haven't even figured out how to send information faster than light pathetic but wait let me guess you've heard that it's impossible to send information faster than the speed of light because physics yes I've heard that too but I think it's wrong and in this video I want to explain why is it possible to break the speed of light limit that's what we'll talk about today if you've been following this channel
for a really long time first of all thank you I know it isn't always easy second you may remember that I already made a video about faster than light travel a few years ago but I think no one understood it in fact when I watched it again recently I didn't understand it either so please give me a second chance because I think it's becoming increasingly relevant to get this right and this time I'll try to do it better I'll even let you leave the toilet seat up in the past year or so there's been a
lot of talk about unexplained aerial phenomena formerly known as UFOs I don't actually believe any of those are of extraterrestrial origin because as I said we're just too boring for aliens to bother visiting us then again what do I know maybe some of those aial phenomena really are space probes from alien species and if we want to properly evaluate How likely that is we need to talk about the possibility of traveling faster than light or at least sending information faster than light because if it's possible at all then that's what the aliens are doing the
idea that the speed of light is a limit comes from Albert Einstein's theory of special relativity yes this guy again the speed of light plays a special role in his theory because it's the only speed that's the same for all observers and just to make sure I mean the speed of light in vacuum the speed of light in a medium any medium is slower than the speed of light in vacuum and it depends on how you move relative to the medium but the speed of light in vacuum does not depend on how fast you move
because there's nothing for you to move relative to I know this sounds about as exciting as flossing teeth but it has some unexpected consequences and I don't mean that your crowns pop off suppose you and your friend let's call him Bob both have a water hose and it spits out water at say 10 km per hour Bob gets on a train which moves at 200 kilm per hour if you live in the United States make that 20 then he turns on his water hose again the water moves with 10 km per hour relative to him
but how fast does it move relative to you you'd expect it to be the speed of the water plus the speed of the train right now imagine you don't have water hoses but laser pointers they send out light with well the speed of light your friend Bob gets on a train again in vacuum of course because this is theoretical physics where people don't breathe cowos spheres and three is either equal to Pi or Infinity depending on who you ask how fast do you see the light of Ops laser you'd expect this to be faster than
the light that comes out of your laser pointer by the speed of the train but not so it moves with the exact same speed as yours because the speed of light is always the same this is what was confirmed with the famous Michaelson moley experiment and it has a very odd consequence you can't catch up with light it doesn't matter how fast the train is light will still move away from it with the speed of light if that didn't make your crowns pop off you've probably heard it so many times before that you've forgotten how
remarkable it is that or you have a very good dentist we can quantify the difficulty of catching up with light by asking how much energy it takes to accelerate an object let's suppose the object has a mass m this Mass corresponds to an energy which is given by the most famous equation ever eal MC square where e is the energy and C is the speed of life but now we accelerate this massive object from zero velocity to some other velocity V the energy un need for this acceleration is the total energy of the object at
the new velocity minus the energy it previously had in Einstein's theory the total energy of an object that moves relative to you with velocity V is given by this expression now if you want to know the kinetic energy you take this and subtract the same expression for zero velocity so you get this somewhat messy expression but don't despair it isn't as bad as it looks for one thing when the velocity V is much smaller than the speed of light then the ratio V over C is much smaller than one in this case the complicated thing
with the square root is approximately 1 + 1 12 V over c² the one cancels out and the C's can out and you get 1 12 MV squ which you might remember is just the kinetic energy but we're more interested in the case where the velocity gets close to the speed of light so V over C gets close to one then this Factor gets close to zero and the entire energy gets close to 1 / Z which is infinity this means if you want to accelerate an object until it reaches the speed of light you
need an infinite amount of energy another way to put this is that the only way you can move at the speed of light is when your mass is zero even a keto diet isn't going to do that for you this is where the idea comes from that the speed of light is a limit that you can't cross but this argument has some issues the first issue is that it doesn't mean faster than light travel is forbidden in Einstein's theory indeed his theory is entirely compatible with faster than light travel the problem seems to be instead
that you can't Accelerate from below the speed of light to above the speed of light it's more like a barrier than a limit the second issue is more a peculiarity it's that on all other occasions when physicists see some quantity go to Infinity they'll tell you that Infinity is unphysical and a sign that the mass doesn't properly work Big Bang black holes non-renormalizable effect of field Theory whatever if there's a singularity they'll say it's a mathematical artifact and not real they don't say that in this case and I think they should the third issue is
that we have a counter example to the claim that one needs an infinite amount of energy to reach the speed of light which makes the argument extremely suspect but to see why I say this I first need to tell you where mass comes from no it's not too much cheese it's simpler than that most of the mass of objects around you isn't really Mass it's binding energy you see almost the entire mass of atom is in the nucleus the nucleus is made of neutrons and protons and the neutrons and protons are each made of three
quarks for the neutrons that's two down and one up and for the protons it's two up and one down quarks not thumbs I mean the quarks do have masses but if you add them together the sum is far less than the mass of either the neutron or the proton instead most of the mass of neutrons and protons is The Binding energy from the strong nuclear force that holds them together we interpret it as mass because E equals mc² but this means it's really odd to put the mass of an object into this equation in Einstein's
theory because really if you look at the object microscopically most of it isn't mass and yes that means most of you isn't Mass either you're almost entirely made of pure energy though when I see how much time you spend watching YouTube I found that hard to believe what with the remaining Mass the part that isn't binding energy electrons and quarks do have masses albe it very small ones these masses come from the hick field not to be confused with the hick boson to be more precise the masses come from the condensed hick field this hick
field condensate fills the entire universe and drags on particles it's kind of like the 19th century ether but with two important differences first the ether was believed to be necessary for light to travel but for the hick field it's the opposite the particles of light the photons are massless which means they don't feel the hix field at all but other particles do feel it when the field condenses it sticks to the particles that slows them down and to us it looks like they have mass another difference between the condensed hix field and the ether is
that the hix condensate looks the same for every one regardless of how fast they move it's just a number at each point in SpaceTime and everyone agrees on what this number is it's like the number of socks in your washing machine doesn't matter how fast the spin cycle is the number of socks doesn't change or if it does I guess it's time for new socks The Ether on the other hand was believed to be basically like a fluid some people would drift with the flow and some people would move against it and they'd see different
things this is not the case for the hick field and its condensate if you like technical terms and I just know you do it's a l and Scala and invariant under Point Transformations okay so the masses of fundamental particles come from the hick field but this is only the case when the field is condensed and that wasn't the case in the early Universe think of an early morning in Spring no not the coffee I mean the dew on the grass where does does it come from well air contains water vapor which means that individual water
molecules float around in the air but warm air can hold more water vapor than cold air if the air temperature drops during the night the water molecules collect to form drops which are too heavy to keep floating and they fall to the ground the hick field has done a very similar thing not in the early morning but in the early Universe in the early Universe it was really hot there was a hick field but it wasn't condensed kind of like the water vapor in the air but then the temperature dropped and the hix field condensed
this condensate now fills the entire universe but it was only when the hix field condensed that particles acquired masses it's a phas transition called Electro weak symmetry breaking and it's believed to have happened at about 10 to Theus 10 seconds after the big bang at a temperature of 10 to the 15 kin that's much hotter than even the center of the Sun what all this means is that in the early Universe none of the particles had masses they were all massless and they were all moving with the speed of light later they were not and
here's the important bit the energy that was released in this pH transition was finite if it hadn't been we wouldn't be here and someone would have written a paper about that I'm sure but the equation that we looked at said earlier said that the difference in energy should have been infinite what gives mathematically it's pretty obvious what goes wrong with the earlier argument if you look at this equation again you see that if this Factor goes to zero but the mass also goes to zero then the ratio can well remain finite this doesn't help us
at all to travel at the speed of light because we can't just UNC condense the hick field even if we could it did basically evaporate The Traveler and I mean I'm not a doctor but that's probably not healthy so this isn't going to let us build a warp drive but it shows that the argument that the speed of light is a barrier isn't even technically correct there is another reason that physicists often bring up for why you can't travel faster than the speed of light which is that it can allegedly cause time travel paradoxes the
argument goes like this suppose Ellis observes a space ship which goes by faster than the speed of light soon here it goes her friend Bob can't afford the new super duper spaceship and lamely zooms by in last year's model at merely 90% the speed of light then Bob would see the spaceship going back in time let's draw this into A Spacetime diagram to see why the horizontal axis depicts One Direction of space so left and right for example and the vertical axis is time a spaceship with which doesn't move according to this axis just makes
a vertical line a spaceship at constant velocity is a line which has some angle to the horizontal by convention a 45° angle is the speed of light Alice just sits there and moves on this straight line and everything that happens on a perfectly horizontal line happens simultaneously according to Alis the faster than light spaceship goes by like this and Bob moves on this line the question is now what Bob sees for this let's look at two particular events and let's make sure those events have a clear error of time from entropy increase let's say someone
drops a raw egg the guy in the spaceship stumbles here and the ax smashes to the ground here this means importantly that time on the spaceship passes in this direction and not in the other direction since Bob is moving relative to Ellis he sees different events happen simultaneously I explained this previously in my video on why the past still exists so well either take my word for it or watch the other video for Bob events that happen at equal times are on these straight lines not on horizontal lines you can then see that for Bob
the order of events is that the egg first smashes to the ground and then gets dropped it seems that for Bob the time order on the faster the light chip is reversed crazy the first reaction you may have to this is who cares what Bob sees I mean you can watch this video in reverse and that doesn't mean I actually spoke in Reverse fair enough the second reaction is to point out that this isn't what either Ellis or Bob see anyway you can't see a faster than light ship coming for the same reason you can't
hear a supersonic plane coming what do you want to see it with instead both and Bob will only see the spaceship after it's gone by and then they'll see it moving away in both directions and again you can say so what I mean gravitational lensing distorts galaxies into rings all right but that doesn't mean the Galaxy is a ring it's just some weird trick on our perception and that's entirely correct but you know physicists have noticed that too thing is this wasn't the entire argument there's a piece missing which goes like this imag imagine you're
a bob and there's really a spaceship that can go faster than light and according to you that goes back in time let's not ask what this means but what you can do with it if the time on the spaceship really goes forward this way then you can give a message to the guys as they come by they take your message to Andromeda hand it over to another fast than light spaceship and the second chip brings the message back to you it would then arrive before you send it this means you could send messages to yourself
back in time and that causes a lot of trouble imagine that this video greatly disturbs you and you send a message to your younger self to not watch it then you'd never have sent the message in the first place so did you or didn't you watch it this type of construction is also called a timel likee closed loop it's a loop in time the argument then concludes that if faster than light Shel was possible that would lead to causality paradoxes so it must be impossible but this argument is also wrong the reason is that just
because according to Bob there's a spaceship going that way with a time that goes forward on the spaceship in a direction that Bob calls backwards in time that doesn't mean if a spaceship goes that way then its internal forward and time direction would be that way if the time Direction on the ship goes that way they can't deliver a message to your younger self instead your younger self can send a message there and nothing's weird about that physicists do have a reason to assume that time on the spaceship could go this way but it's not
a good reason it's because in special relativity all observers must be treated the same way in special relativity if you think that this is possible then that must also be possible but special relativity is special because it doesn't contain gravity and this means it doesn't actually describe reality for this we need general relativity and while the time travel argument is correct in special relativity it is not correct in general relativity I know this video is some tough goinging so let's stop for a moment to appreciate where we are I summarized the usual argument for why
faster than light travel leads to time travel paradoxes I'm about to explain why this argument doesn't apply in the real Universe the usual argument uses special relativity According to which only relative velocities are physically relevant in special relativity you can't be at a velocity of absolute zero that just makes no sense but the real Universe contains stuff as you've probably noticed you can take all this stuff calculate the average velocity that it moves with and then you can Define absolute add to be motion that has no relative velocity to the average of all that stuff
since you like technical terms so much it's called the co-moving frame it's the reference frame that moves along with matter in the universe we are currently not at rest relative to the average of stuff in the universe because the earth goes around the sun and the Sun goes around the center of the Milky Way and the Milky Way is rushing towards something called the biger tractor that no one really knows what it is if you wanted to be at rest with the universe you'd have to run at 300 km/ second into this direction uh no
wait uh this uh or this all right so there's matter in the universe that moves one way and not another but what does this have to do with the time travel story suppose you're aess again but now you're Alis in a universe with general relativity and you're moving with the stuff you are in the co- moving frame and now assume that faster than light travel is only allowed forward in time in this particular frame in this case you can't make loops in time regardless of what Bob thinks he sees the co-moving frame defines One Direction
as forward in time the only thing Bob can do is send two signals to endomet and there's nothing paradoxical about that you may Wonder now what the motion of matter should have to do with the possibility of faster than light travel this is a very good question to which the answer is quite possibly nothing I just Ed this as an example it's an example to show that faster than light travel does not necessarily imply time travel paradoxes the letter just doesn't follow from the former to add one final reason why you shouldn't trust the argument
that faster than light travel is impossible is that we know our current theory of SpaceTime general relativity can't be correct because it doesn't work together with quantum theory this is why we need a theory of quantum gravity and we still don't have one we know however that causality and locality become really screwed up in quantum mechanics and the same is probably the case in quantum gravity this is why I think it's extremely implausible that any argument about faster than light travel would survive in the to be found theory of Quant gravity of course you already
knew that no one's figured out how to travel faster than the speed of light yet but I hope I've managed to convince at least some of you that the formal reasons you may have heard against it are on shaky grounds this is why I believe physicists should think a little harder about faster than light travel at the very least then maybe humans wouldn't be so boring when I was in Middle School my physics teacher told me that very few people understand Einstein's theories maybe that was once correct but I can very confidently tell you that
it's no longer the case today I believe that everyone can understand Einstein's theories today but passively watching YouTube videos won't get you there you have to actively engage with the material our sponsor brilliant can help you with that brilliant.org offers courses on a large variety of subjects in Science and Mathematics and they add new cont content every month the great thing about their courses is that they're all interactive with visualizations and follow-up questions so you can check your understanding right away to get some background on the physics in this video check out for example their
course on special relativity it'll shed light on how it really works with the reference frames and the Lawrence Transformations when I need to freshen up my knowledge or want to learn something new first thing I do is look it up on brilliant I now even have my own course on brilliant which is an introduction to Quantum Mechanics it covers topics such as interference superpositions and entanglement the uncertainty principle and bells theorem it's a beginner's course that you can take without prior knowledge and you can then build up on this maybe with their courses on Quantum
objects or Quantum Computing if you're interested in trying brilliant out use our link brilliant.org Saina and sign up for free trial you get to try everything brilliant has to offer for 30 days and the first 200 subscribers using this link will also get 20% off the annual premium subscription thanks for watching see you next week
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