Sabine
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I think it's possible to travel faster than light. Here's why.
🕑 Added 2023-04-08 12:00:02 +0000 UTC[This is a transcript of the video.]
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, er, 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 made a video about faster than light travel already 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 extra-terrestrial 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 aerial 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 travelling 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 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 kilometres per hour. Bob gets on a train which moves at 200 kilometres 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 kilometres 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, cows are spheres, and 3 is either equal to pi or infinity, depending on whom you ask. How fast do you see the light of Bob’s 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-Morley 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, E equals m c square, where E is the energy and c is the speed of light.
But now we accelerate this massive object from zero velocity to some other velocity, v. The energy you 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 one plus one half v over c square, the one cancels out and the c’s cancel out and you get one half m v square, 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 1. Then this factor gets close to zero, and the entire energy gets close to one over zero, 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 maths doesn’t properly work. Big bang, black holes, non-renormalizable effective field theory, whatever. If there’s a singularity, they’ll say it’s a mathematical artefact and not real. They don’t say that in this case, and I think they should.
The third issue is that we have a counterexample 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 atoms 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 neutron that’s two down and one up, and for the proton 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 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 m c square. But this means it’s really odd to put the mass of an object into this equation in Einstein’s formula. 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 find that hard to believe.
What’s with the remaining mass, the part that isn’t binding energy? Electrons and quarks do have masses, albeit very small ones. These masses come from the Higgs-field, not to be confused with the Higgs-boson. To be more precise, the masses come from the condensed Higgs field. This Higgs-field condensate fills the entire universe and drags on particles. It’s kind of like the 19th century aether, but with two important differences.
First, the aether was believed to be necessary for light to travel. But for the Higgs-field it’s the opposite. The particles of light, the photons, are massless, which means they don’t feel the Higgs field at all. But other particles do feel it. When the field condenses, it sticks to the particles. That slows them down and it looks to us like they have a mass.
Another difference between the condensed Higgs-field and the aether is that the Higgs-condensate looks the same for everyone, regardless of how fast they move. It’s just a number at each point in space-time 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 aether 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 Higgs-field and its condensate. If you like technical terms, and I just know you do, it’s a Lorentz-scalar and invariant under Poincare transformations.
Ok, so the masses of fundamental particles come from the Higgs-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 it come from? Well, air contains water vapour, which means that individual water molecules float around in the air. But warm air can hold more water vapour 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 Higgs field has done a very similar thing, not at night, but in the early universe. In the early universe it was really hot. There was a Higgs-field but it wasn’t condensed, kind of like the water vapour in the air. But then the temperature dropped, and the Higgs field condensed. This condensate now fills the entire universe. But it was only when the Higgs field condensed that particles acquired masses.
It’s a phase transition called “electroweak symmetry breaking” and it’s believed to have happened about 10 to the minus 11 seconds after the Big Bang at a temperature of 10 to the 15 Kelvin, that’s much hotter than even the centre 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 phase 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 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 uncondense the Higgs field. Even if we could, it’d basically evaporate the traveller 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 Alice observes a spaceship which goes by faster than the speed of light. Zoom there 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 percent the speed of light. Then Bob would see the space-ship going back in time.
Let's draw this into a space-time 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 which doesn’t move, according to this axis, just makes a vertical line. A spaceship at constant velocity is a line which moves at some angle. By convention a 45-degree 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 Alice.
The faster-than-light space-ship 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 arrow of time from entropy increase, let’s say someone drops a raw egg. The guy in the spaceship stumbles here, and the egg smashes to the ground here. This means, importantly, that time on the space-ship passes in this direction, and *not in the other direction.
Since Bob is moving relative to Alice, 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 of the faster than light ship 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 Alice 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 Alice 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, alright, 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.
Imagine you are 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 faster-than light spaceship, and the second ship brings the message back to you. It would then arrive before you sent 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 time-like closed loop, it’s a loop in time.
The argument then concludes that if faster-than-light travel 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 space-ship in a direction that Bob calls backwards in time, that doesn’t mean if a space-ship goes that way then its internal forward-in 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 space-ship could go this way, but it’s not a good reason. It’s because in special relativity all observers must be treated the same. In Special Relativity, if you think that this is possible, then this 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 going so let’s stop for a moment to appreciate where we are. I summarised 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 rest 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 centre of the milky way and the milky way is rushing towards something called the big attractor 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 kilometres per second into this direction. No, wait. This. Or, this?
Alright, 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 are Alice again but now you are Alice in a universe with general relativity and you are 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 Andromeda, 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 used this as an example. It’s an example to show that faster-than-light travel does not necessarily imply time-travel paradoxes. The latter 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 space-time, 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 quantum gravity.
Of course you already know that no one’s figured out how to travel faster than the speed of light. But I hope I have 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 this.
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Thanks for watching, see you next week.
Comments
By Arthur Henry Reginald Buller, in Punch Magazine, 19 December 1923
There was a young lady named Bright, Who travelled much faster than light. She set out one day In a relative way And came back the previous night!
Jeffrey, my hope still resists against that
Tanj
Where does the 'co-moving frame' come from, and why should we assign it any reality? We have only frames of reference. The EPR puzzle illustrates that attempting to explain reality from a universal frame cannot work. The 'multi-verse' solution is not the comic book version. It is the same solution as special relativity: multiple frames of reference.
Great video and thought provoking stance. Appealing idea that aliens just aren’t interested in us EM-communicating species. Have thought that it was tenuous that FTL necessarily implies time travel … sure it can make an effect appear to happen before the cause, but an observer aware of the speed of light can reasonably infer the sequence of events. The notion that we must go back in time based on the space time diagram presupposes that nothing can travel FTL in a vacuum. So we shouldn’t expect math/thought experiments based on the theory that FTL is impossible to be valid in an FTL regime. While this makes sense to me, it’s quite rare to see a physicist by career take such a bold position that breaks from the mainstay narrative. I know it’s not the only thing you disagree with the mainstream about, but this dogma is virtually untouched. Great topic and can’t wait till we can hear what pillar will drop next. Maybe this notion of dark matter. G << ke; so could a very small galactic polarization fix the rotation curves with similar considerations for the Big Bang leading to CMB echos
Exploring other habitable worlds makes sense and is but an extension of what civilizations do. However, I think that it is a delusion in most cases because, as with earth, there is probably but one truly habitable world in any given solar system. For example, Mars is not habitable beyond small, Antarctic colonies. Therefore we need to focus on reversing the damage we cause and reduce our load to allow the earth's natural system to function to support life as we know it. I see the same situation throughout the universe as most planets have cleared spaces around themselves and thus most systems would have a very small number, one or two, planets on which liquid water would exist that would permit the chemistry of life as we know it to develop. Civilizations need to focus on protecting the natural systems in which they developed, reject ideologies that promote some special status that allows them to believe that they are the center of creation with no obligations. BTW, I do not accept 'longtermism' at all. What matters is the here and now, not some future time as all that matters are the living, their pain and suffering.
Rad Antonov
Do you think it makes sense for an intelligent civilization to invest in “exporting” life from its home planet to potentially habitable worlds in other solar systems? We might soon have a handful of potential targets and while no one individual can expect to make the journey to one of those, a robotic probe loaded with DNA samples and a way of “seeding” some life forms might have a chance. Is it worth a try?
Actually, I don't see intelligent life as a rarity, chemistry is the same throughout the universe and so if the conditions are right then life should result and evolve similar to here, but I do see that advanced life as more rare. This is because I think that advanced life does what we are doing, overpopulating and running their planet's ecosystems into dysfunction to the point that they drive an extinction event that ends their reign, drives them either into extinction or a total collapse of their civilization that can't recover. That's why we haven't received any signals, they winked out too quickly.
Agree, perhaps our solar system is not the only one to allow life, but I think it's a rararity. Happy to live here on an exceptional jewel, first task is to save it for future.
Spot on! People get deluded by sci-fi, they believe that we can tech our way out of any situation, when we can't. Your example of biosphere is a very good one. While we have been able to live in space for extended periods, we restock from earth, the space stations are not closed systems. We really need to act now to allow our ecosystems to heal, to reduce the human load and develop closed-loop, sustainable economies before the current extinction event becomes irreversible.
You've put into words pretty much exactly how I feel, both about FTL travel and escaping the solar system. I used to think that generation ships might work as a permanent human habitat, but the biosphere experiments in the AZ desert pretty much killed that for me. Yeah, there were technological things that failed with the biosphere experiments, but the psychological and social problems with the people were much worse and will be much harder to solve if long term interstellar travel is ever to become a thing.
While there exists the possibility of faster than light travel, I doubt any physical construct, such as a ship, will ever get fast enough to make interstellar travel practical, the distances are simply too great. Any advanced civilizations that comes into existence are therefore constrained to their home solar system, if they don't kill themselves off by destroying the ecosystems of their home world, that is. That wouldn't be that bad as there are more than enough resources in other system bodies to meet the needs of any civilization, so long as they don't overpopulate and destroy their home's ecosystems, that is.
Mark Behets: Maybe you don't have to wait long for this; it has happened already. It was seen in the experiments of A. Riess and S. Perlmutter (both with Nobel Price). The plausible explanation of their results is not dark energy - this was not found and will not be found. It is the conclusion that the speed of light was higher in former times than today (reference to the Doppler Effect). Admittedly, Perlmutter did not follow this explanation, but also he could not give me an explanation for the so called “Dark Energy”.
Absolutely brilliant. If ever empirical evidence is found that faster than light travel is possible, this video will become part of the history of science. I hope this will happen.
Rad Antonov
Hi Sabine, yes, exponentially damped because f=sqrt((1-v/c)/(1+v/c)) spits out an imaginary value when v>c, like an imaginary index of refraction that limits the wave propagation. For a moment I thought the intrepid astronauts might be fried by the infinite energy of the CMB they’ll see as they go through the barrier, but they didn’t accelerate past it, so they’ll be fine. Lorentz transformations also seem to go haywire but we are going FTL, who needs those?!
You're right of course, saying that the argument for why it's impossible doesn't work doesn't mean it's possible. But enough for me to believe it is possible... I don't understand what you mean by imaginary frequencies there. (That would be a damping factor.)
Tom Tomm
Warp 10 woooo!
“The argument then concludes that if faster-than-light travel was possible, that would lead to causality paradoxes, so it must be impossible.” Which means that we have here a theory which is not at all robust but behaves critically for unexpected observations. And it has singularities. I think we agree that nature does not have singularities. Is this theory necessary? No, it is not. Because the version of relativity following Lorentz does not have these weak points; but it has, on the other hand, exactly the same results as the version of Einstein for the real observations. And this includes the cases of General Relativity.
D Brown
P.S: I believe it is not so unlikely that extraterrestrial UFOs have been seen from earth, but I feel it is a small percentage of what is actually reported. I say this because, 1: Lying and filing a false report are grounds for a dishonorable discharge in the military. I feel it is unlikely commercial and military pilots would risk ending their ability to be a pilot by reporting something they did not see. I also do not believe that as a group they suffer from bouts of hallucinations. 2: In a million years, assuming we don't blow it all up, people from earth will be visiting other stars. What do you think they would do if they came across a planet where people were at war with each other and were making their planet uninhabitable at an accelerated pace? Would the people on such a planet be considered an intelligent species? Would the people on such a planet be considered safe to engage?
D Brown
“I know this video is some tough going...” 1: This was the first statement I understood. 2: I am glad to have someone like you who is serious about explaining such complex topics. There will be a time when my job is not as demanding. At that time I will enter my hobbyist phase in life and will get better an consuming your lectures/content.
I can indeed confirm that astronomers count 1, 2, infinity. This does present problems when trying to determine how many licks it takes to get to the center of a Tootsie Roll Tootsie Pop or when deploying a Holy Hand Grenade. In a similar vein, I can also confirm that element 1 is Hydrogen and elements 2 and up are all metals. I can appreciate that loopholes exist for the standard arguments against FTL travel (or information flow). What I find most rewarding about this video, though, is reintegrating bits of knowledge that I already have to come to an 'aha' moment -- of course, if GR isn't quite right and QM is squirrely with causality, then any future QG theory might not explicitly preclude FTL travel; it might, it might not, we just don't know at this time.
I'm on board
The video is such a smart and entertaining Easter present. I was quite astonished, when I heard some years ago the first time, that the mass of three quarks is just a tiny amount of the protons/neutrons mass, and all the rest comes from gluons changing into pions/sea-quarks and back and changing color, and all this is the strong force and this chaotic pap brings exactly the right mass to an atom. Perhaps one time a video about that? Understand better now, how Higgs field works, and that it condensed in the early universe, thank you
Rad Antonov
Interesting, though I am not sure that just because the argument avoids a time travel paradox it makes FTL travel possible. What if you chose the CMB as the reference frame and asked what the Doppler shift is wrt to it? Wouldn’t that give an imaginary frequency for the light? Not necessarily a show stopper if there is a sensible way to modify the formula. Or maybe it means light is exponentially suppressed and you can’t see anything when gong FTL.
“Because the speed of light is always the same. This is what was confirmed with the famous Michaelson-Morley experiment … “ Was it really confirmed? Hendrik Lorentz has shown 15 years before Einstein that this result has a straight physical cause: objects contract at motion with respect to some reference frame. This is caused by the fact that any field contracts at motion. And this again follows from the model that fields are mediated by exchange particles. Because if the motion of the exchange particles is transferred into another frame, their path changes in a way that the according field contracts; and so molecules contract and in the consequence objects. And it does so by the Lorentz factor. At the time of Lorentz this was understood as an assumption. But from the present knowledge of the setup of matter it is an unavoidable consequence. So, the constancy of c in every frame is a measurement result only. Which BTW makes the treatment of physics much easier. Einstein was educated to appreciate a world which is dominated by structures. So he was reluctant to follow the view of Lorentz.
Jason Bolton
My plan is to move an inertial reference frame at rest with a surrounding cylinder volume that is a black hole on the top and a white hole on the bottom.
Thank you Sabine, this is brilliant ! I will have to watch this a few times .. As I don't really understand time. I can see how faster-than-light speed could work if the time direction changed, but wouldn't we see that as something moving below the speed of light, and wouldn't that imply a "mirrored" general theory of relativity, with different laws adapted to that situation ? But no need for such complicated stuff... I am already stuck at the point where photons don't experience time. I can't visualize that, as everything I see is bathed in time. But it makes me think it's not implausible that they could be in two places at once, until the collapse of the wave function. The 'until' here implies time, and they don't see time. Maybe time is a dimension that condensed early on like the Higgs field?
