Bartender says "We don't sever faster then light particles here". A tachyon walks into a bar.

PBS Space Time: my favorite show I don't understand.

Whenever I watch these I start out understanding what he's talking about. Then I think I know what he's talking about. Then I pretend that I know what he's talking about. Then I confess that I have no idea what he's talking about.

"My ship is _so_ fast, that it can beat _itself_ in a race!"

"It's possible to receive a reply to your message before the message is sent." I must be using a tachyonic anti-telephone when I ask girls out

Kudos to the person who makes all these diagrams... phenomenal job!

This video reminds me of a joke: Two cows are talking and the first says "Most people abbreviate PI to 3.141592 but in reality the decimals go on for infinitum". The second cow replies "Moo". I feel like the second cow after watching this video.

Enough talk! Lets build that ship and really see what happens!

"before Albert showed us the way" love it

7:31 "The Paradox appears to materialise out of nowhere and then proceeds to split in two" Woah, Prof Matt just scienced the Picard Manoeuvre!

"We are temporal creatures, our experience of the universe is a thing that emerges from the forward causal evolution of the matter that we're composed of." Thought this was such an articulate way of describing reality.

"In the olden days, before Albert showed us the way..." Beautiful

If you have a valid idea for building a time machine, you will most likely be getting a visit from your future self, warning you to never build it.

I have no idea what the fuck he is saying But i like it

He has a unique way of sounding interesting while simultaneously making you feel like you have no friggin idea what he just said.

You can't do a lorentz transformation between a ship in a warp field and one in normal space time, thats kind of the whole point. In a warp field you are effectively removed from the rest of space time until you reach your destination. No light or any information travels between the two points. Because for spacetime itself the speed of causality is infinity as present in blackholes an inflation period where spacetime streached at a rate greater then C. So you can't change reference frames from inside a warp field to outside one using mathematics designed for a normal space time, not more then a photon can escape across the event horizon outside of a black hole. The warp field solution to get around C is not just to get fast, its to get around the limit of a lorentz transformation control universe where FTL is indeed impossible. It does this by not violating any rules but by placing the mass it wants to transport in a kind of bubble universe and then move the bubble. The only interaction between the two areas is not light or any particle but vacuum energy (so possibly virtual particles) which quantum field theory says exists, at least partly, due to the wave particle duality. Basically we can't mathematically model an FTL ship correctly because we don't have a theory of everything that balances out relativity and quantum mechanics. Thus this shouldn't be a way to disprove FTL by its nature, rather it shows a flaw in our current theories, a flaw that is very well known. Or in other words, we can't model FTL very well until we at least figure out Dark Energy as Dark Energy probably involves vacuum energy of some kind on the macro scale but using the current equations the numbers are widly off. This is just another manifestation of that discrepancy between the two models.

Literally sent my solution an hour ago! Dang, better get on my FTL spaceship so I can submit it a little earlier

Hmm, yeah. I understood some of those words.

this show is just awesome. I would love to see some history on the experiments behind these theories, trying to understand how these strange notions were originally devised.

About 20 years ago I was writing a screenplay about sending a message to the past. I emailed Kip Thorne (who was about 58 at the time) to ask him if my messaging idea was possible. He replied "No"...I then replied to him: "That's not what you told me at your 65th birthday party!" (True story)

Any chance we can get a string theory video?

You lost me on this one. lol

fantastic content and delivery as usual. visuals on point. amazing stuff! thanks!

"..objects returning to their origin before they depart"... I had to put down my drink... Damn you PBS... Damn you

Great video, but I disagree with the statement that an observer on the Annihilator sees the Paradox travel forward in time. To get the velocity of the Paradox relative to an observer in the Annihilator, use the formula for velocity transform between relativistic reference frames and you get u' (velocity of Paradox relative to Annihilator) is infinite as observers on the Annihilator would see the Paradox leave the Earth and arrive at the destination at the same point in time in their reference frame. en.wikipedia.org/wiki/Velocity-addition_formula

The EVE Online Tengu at 4:30 though

This is easily my new favorite channel!

After watching this video twice, i understand it and i'm fascinated as always.

Love your series! I recently came across this: In 2016 a Japanese physicist, Dr. Takaaki Musha, wrote a paper entitled, “The Possibility of FTL Space Travel by using the Quantum Tunnelling Effect through the Light Barrier.” Any chance you can look at/debunk this?

OK, this video forces me to come to the conclusion that I'm dumb 😂

God these vids are just too awesome. Please keep up the awesome work guys :) Great channel!

All of these PBS youtube shows are amazing

Except.... Aren't the Paradox and it's crew isolated from the effects? It was my understanding that the space it's self moved, protecting the crew from time dilation and causality violations. If that's the case, what does the diagram for the *crew* look like?

Thanks for the cool video. I was just talking to a friend last night concerning time dilation and space travel and I was wondering what are your thoughts on what we discussed. Essentially he had asked me what would happen if we were to be able to travel at the speed of light. I told him that we would approach infinite mass and would take more and more energy to be able to travel faster and that time dilation would become an issue. That said though, I told him it is possible that we could accelerate to a significant fraction, as much as 75% with traditional means given some time and some assistance of gravity assists through very careful navigation. He was surprised and asked if that meant that we could travel to other planets and I responded yes, we could, but that the time dilation would be a problem. At 75% the speed of light I roughly calculated (very roughly based on a post saying that it roughly goes at the square of the percent speed of light difference) that the time dilation would be on the order of 1 second = 1 minute to the observer, or 60X the difference. At that speed it would take around 5 1/4 to 5 1/2 years to reach our nearest neighboring system, but to people outside the ship almost 300 years would have gone by. Then factor in a return trip and 600 years. In that time, we'd probably have better technology such as warp drives where space is warped so that the time inside the bubble and the time to an observer would be the same. Using these warp drives would allow us to travel faster than light without the undesirable effects of time dilation and increase in mass. I did note that it would take a lot of mass to create a warp bubble and there is also the problem of forming and collapsing the bubble, but that through clever math, the mass needed has been reduced from a solar system mass down to around a planet Jupiter size mass, so in the 600 years, we could possibly solve this issue. That brings up an interesting question I pose to you (and anyone interested in postulating with me), namely, assuming all the other issues such as fuel, acceleration, deceleration, etc. were also solved and given that by the time a ship would reach our nearest neighbor would likely be longer than the time to solve the issues with creating and using warp bubbles, should we even send ships towards these distant objects, or should we wait until we have warp bubble technology? On the one hand, we can gather information in the mean time of what lies between, and there is no guarantee warp bubble technology will be feasible in the intervening time, but on the other, if warp technology is developed, the travelers would only find themselves arriving to an already populated planetary system...Exploration of our own solar system is a given as it is on the scale of 20-30 years travel to the edge and greatly enhances our understanding of how the universe works, but missions to other solar systems...that is the big question. What are your thoughts? Some other things to consider if we do use warp bubbles: All space objects positions and velocities would probably need to be noted for two reasons. The first is that while small objects (under a cm) probably would become just dust as I understand it, the effects of warping through larger objects, especially planets (heaven forbid stars or gravity wells) is largely unknown guess work. The second is that if you do need to avoid going through objects, you can't just rely on their observed current positions. Even observing Mars from here on Earth, we are seeing minutes into the past. In fact, if the Sun were to explode, we wouldn't know for 8 minutes. So if traveling at warp speeds, we would need to know their current actual positions. Also, how far out from a target planet would we need to stop or start our warp bubble capable ship? Too close and it might rip the planets apart. Could we even enter another planetary system, let alone construct our warp bubble within our own? Or would the planetary mass destabilize the orbits of all the solar system objects? Even a Jupiter size mass object being positioned anywhere in our system would probably destabilize it, so are warp bubbles even possible for space travel? Finally, how in the heck do you shift a planetary size mass so as to create the bubble to begin with and shift it back to collapse it at the destination? I imagine the one pebble at a time argument here would not work, but maybe it could?? If so, at what point does acceleration due to gravity stop and the bubble form where you are able to travel faster than the speed of light? Would this method violate general relativity? Logic? My mind? (Definitely the last one...it is starting to hurt, so I'll stop here.) What do you think?

I've thought about this for a long time and it just makes sense

took the survey; glad to help in my small way!

*Before* you transform the perspective to the "near light speed traveler", draw the path of the space ship traveling back to Earth. It will arrive in the future in Earth's perspective, as it should. Now apply the transformation to *both* paths, and it can easily be seen that the slope of the ship's return path is > 45 degrees, traveling correctly into Earth's future even in the near light speed perspective, instead of the arbitrary < 45 degree line you've drawn traveling into the past. But hey, doesn't FTL travels have slopes < 45 degrees? Yeah, *from Earth's perspective!*

when you see the stars, you see them in the past. the time it took light to reach your eyes. it is the same thing here. The annihilator sees the paradox in the past. the time it took light from the paradox to reach annihilator by the distance between the two. when the annihilator sees the paradox, it has already travelled the distance travelling twice the speed of light by the time it took light to reach the annihilator. real-time, they are not seeing each other travelling at their own speeds towards their own directions every second. real-time they are both traveling with every passing second. both ships experiences the same time. real-time they both exist on the same space at the same time.

The only youtube video that blows my mind in 5 secounds

Did your survey....hope it helps! Keep up the good info!

Love these vids, thanks guys. Also.. my first ever first comment on any YT vid! :)

oh my god i just realized they did this in star trek. this is the picard maneuver!!!

Survey complete. I hope you find my feedback useful. I wanted to reiterate here though what an outstanding show you guys produce. Don't fret too much about Patreon rewards. The show is the reward.

4:21 Matt I want that song! :) Love it! Great work Matt!

I'll be the first to admit that the mathematics behind this are beyond me. They are farther advance than anything I have formally studied. That said, it feels to me like there's something being misinterpreted to reach the conclusions reached in this video. I think the problem is choosing a reference frame. Would there not be some reference frame that is static to the fabric of spacetime, and then therefore that any other is therefore relatively in motion and then no longer able to be treated the same under transformation? Like, if that 2c ship were to fly for 50 years, turn around, then fly back for 50 years, wouldn't 100 years have passed at its point of origin? The ramification of time dilation is that maybe time would have to flow backward on the ship, but clearly that doesn't make physical sense (hence the asymptotic energy boundary in accelerating past c... that results from the dilation of time such that time effectively stops at c... sort of like a zeno tortoise, but with increasing speed instead of advancing position. As time slows down, the power it takes to provide more acceleration grows infinitely and crossing that c boundary, at least from the perspective of the ship, would require infinite power since at c, time no longer passes.) We try to get around this by invoking the notion of an Alcubierre drive so the ship is contained in a spacetime bubble and does not experience dilation. Wouldn't this then eliminate any of the time travel aspect of FTL? Suppose a completely static frame is trapped in the bubble and translated through the galaxy at 2c for 50 years in one direction then 50 years back... assuming negligible relativistic effects at the origin point, pretty much both the bubble and the origin would have experience 50 years of tick-tock on the watch. The more I think about it, the more I'm driven to the conclusion that the discussions in this video and the few preceding it are what Fermi would have called "not even wrong."

The Tengu isn't known for its speed.

Sub loom in all LOL, space puns are hilarious, especially the confounding of weaving, with moving swiftly through space. Though, curiously one does move faster when secured in place.

Just the trick to starting the day! Now working on the car this Saturday doesn't seem all that of a problem to tackle. Cheers.

If the Alcubierre drive works as intended, wouldn't the extreme induced curvature of spacetime and the moving spacetime itself break the flatspace diagram, rendering this simplified analysis invalid for the specific case of the Alcubierre metric?

I haven't dug through ALL of the comments, so this might have been brought up before. There was, as far as I can tell, a slight error in this video about the speed of the Paradox in the Annihilator's frame of reference at about 8:00 minutes. The two points in space-time that we're interested in are the launch of the Paradox and its arrival at the planet. The first one is at position x1 = 0 (i.e., at the earth) and t1 = 100 years. The second is when the Paradox arrives at the planet, x2 = 100 LY and t2 = 150 years. We can now use the Lorentz Transformation to find these two points in the Annihilator's frame of reference. The velocity v = 0.5 LY/year. Therefore, the Lorentz factor is 1/sqrt(1-v^2/c^2), or 1/sqrt(1-(0.5)^2) = 1.1547. t'1 = 1.1547(100 years - (0.5 LY/year)(0 LY)/1^2) = 115.47 years. t'2 = 1.1547(150 years - (0.5 LY/year)(100 LY)/1^2) = 115.47 years. In the Annihilator's frame of reference, the Paradox leaves Earth, passes the Annihilator, and arrives at the planet all at the same time. I will leave the calculation of the x locations in the Annihilator's frame as an exorcise, but they are not the same. Another way to consider this is that the speed of the Annihilator (in Earth's frame) is 0.5 c. The Paradox's speed is 2.0 c. Given the conventional arrangement of a space-time diagram, these are the inverses of the slopes of the "world lines". They are also the inverses of each other, so they are symmetric about the speed of light, which is always a 45 degree angle, or a slope of 1. If we transform to the Annihilator's frame, its world line is now vertical. That doesn't break this symmetry, so the Paradox's "world line" is still symmetrical about the speed of light line, so is horizontal. It is everywhere at once. Thank you, Tim

I love this channel so much.

I.... am picking up the pieces of my scattered over the room. Mind blowing

At 6:57 Actually, the paradox is not traveling forwards in time wrt the annihilator. The "world line" of the paradox is perfectly horizontal (with the numbers you gave) in they annihilators frame. Remember the annihilator time axis in earth frame has slope v, or 0.5, which is the same slope 1/v, or 1/2, of paradoxs "world line" in that frame. The journey would appear instantaneous.

Can you go back in time (via FTL round trips) in order to refuel with the same stuff you consumed to go FTL in the first place?

I'm so happy that you mentioned a Sophon!

Thank you. That was clear and clarifying.

What I find hard to believe is the idea that simply passing one's own photons places someone physically into the past instead of simply being ahead of the range of visual perception.

Step #1 Load some Moscovium (Element 115) into a mini particle accelerator with an add-on heat-to-electricity converter. Make sure your Moscovium has 115 protons and 184 neutrons so that the half-life is greater than one hundred years. Step #2 Shoot a proton into your Moscovium so that it becomes Livermorium for a split-second before reverting back to Moscovium. Inverse beta decay happens, and the proton becomes a neutron plus a positron. The neutron undergoes beta decay, and becomes a proton plus a neutrino plus an electron. The positron and electron collide, and release energy. The neutrino hits another proton in the nucleus, and causes another inverse beta decay. Step #3 Use the energy from the positron/electron collision to amplify the [strong nuclear force] holding the Moscovium together such that the gravity field envelops and encompasses your space-faring ship. This creates a bubble that is outside the normal space-time fabric. Step #4 Travel faster-than-light by creating a gravity down-slope in front of your space-faring ship using focusing amplifiers that bend space-time in front of your ship. This causes your bubble to be in constant free-fall in a given direction until you stop focusing or turn-off your mini particle accelerator. Step #5 Laugh and enjoy this bit of fiction ... or is it fiction? lol (taken from Area 51 forums/threads/posts)

took me forever to re-find this, i'll have to like it.

Love this show. Thanks so much!

"traveling FTL is traveling back in time" Only if done in normal space. Alcubierre drive distorts space-time but doesn't transit the passenger backwards in time.

"Rolling down the causality hill" I'm going to need a helmet.

Another cool video. It's been pretty well known that FTL travel will take you back in time (first Superman movie, for example), but I'm surprised no one had mentioned how this is a solution to the twins paradox. Here's a challenge question: how much faster than light would you have to go in order to arrive at Alpha Centauri exactly when you left earth (assuming instant acceleration). :-)

Such a unique utube channel never change please

But by definition the warp drive ship is not "moving" its warping space in front and behind it.

"They've gone to Plaid!"

Wow!!!love this amazing video . Thank-you,.

So to the captain of the annihilator sees your ship spontaneously appear out of nowhere and split in two opposite directions? correct me if I'm wrong but doesn't that sound similar to how subatomic particle pairs appear out of nowhere and immediately annihilate each other? I think I'm just connecting unrelated patterns but it would be interesting if there was some connection there.

Hi, isn't that so, that with Alcubierre drive creates a bubble of flat space, so that the reference frame of the observer on Earth and the occupants of the spaceship remain the same ? Therefore, the diagrams You presented do not apply to the Alcubierre drive powered spacecraft, and also time travel is excluded.

Finally I understand why this video ran backwards, when I was watching it the day before it came out!

Now that I know the answer lemme get in my FTL spaceship, go back in time and send the correct answer...

If travelling superluminally is *fundamentally* the same thing as time travel, how does this affect galaxies that move away from each other superluminally due to the expansion of the universe? Shouldn't we see weird time-travelling affects from this?

As a fan of Liu Cixin, I was pleasantly surprised to see a nod to his "The Three-Body Problem"/"The Dark Forest"/"Death's End" trilogy. Though he does play fast-and-lose with some things (like the Alpha Centauri system and quantum entanglement), his speculative physics is interesting and his notion of weaponizing physics is terrifying. Wallfacer Matthew O’Dowd, I am your wallbreaker. ;-)

Nice video. I am always delighted when Pr O'Dowd dives into the realm of Sci-fi to demystify it BIG TIME. We cannot help but dream of doing FTL travels, simply because we do not enjoy the thought of witnessing our own world lines disappear. Ironically, fancy FTL travel is the number 1 pathway for destroying our own world line. (Number 2 being an enthusiastic jump into a BH's singularity, of course). Still, what a cool way to die...

Wouldn't faster than light speed travel do wacky things to the matter of travelling particle? How would a particle of finite mass behave under these hypothetical conditions, and what's the overall heat balance of the journey?

invalid... a Tengu can jam the ship before enter in wrap. the tengu .. such op ship I love Caldari ships

this is the best youtube channel to watch while smoking weed,hands down.

Keep doing what your doing!!

In theory couldn't super light speed particles exist but just have no way of interacting with our sublight speed particle based perception of the universe?

How many answers to the challenge do you usually recieve? Just trying to figure out the probability of winning a shirt. :D

Mind-bending. I have more reading to do about the conformal diagram of a fully extended, Schwarzschild black hole...the somewhat complex version jotted down in my notebook has some fundamental time dilemmas that need working out.

JUST BLEW MY MIND. I guess I'm staying on earth and traveling no where. DAMN

I am sorry but, I have an unrelated question. If PBS experiences budget cuts, would it effect the funding for PBS supported KZfaq channels? PBS Space Time, Brain Craft, Physics Girl, It's okay to be smart, PBS Infinite series, I am subscribed to all of them, and I am a little afraid that I could loose some of my most favourite channels. Thanks for responding in advance, and if you wanna stay out of political stuff, I would understand.

Δt' = Δt / √( 1 - ( v² / c² ) ). If v > c, then 1 - ( v² / c² ) < 0. That makes √( 1 - ( v² / c² ) ) imaginary. That makes Δt / √( 1 - ( v² / c² ) ) also imaginary. That makes Δt' imaginary. Which means you aren't going backwards in time. You're going sideways in time, since that's what imaginary numbers do in directions. Weird.

Insane!! Hats off

Beautiful video. Nice shout out to Sophons! Three Body for the win!

I love Astronomy!

Maybe this would make more sense if I smoked one before watching.

Glad I found this!

I'm so happy for the eve memes :D

So by my understanding, by traveling faster than light, one could catch up to the photons which havent yet been intercepted by other matter, but that's all they'd be. Photons. Even then, you'd need to gather all of the photons which have spread out over massive distances in order to get a coherent picture of one singular point in the past. This essentially would mean that speed alone is not enough to travel through time in any real way. You'd just be catching up to emitted photons.

In my opinion, traveling back in time is not possible, but into the future is sort of possible. But how could we ever travel back in time, when things don't exist anymore ? Just the light remains to show us what there was, but it ain't actually there anymore. So stop with back traveling in time, we already proved that it won't be possible ever. This is not how the space and time works, it's a linear event, when it past, it dies, what we see is only the light of it, but if you manage to go faster than the light itself, which is not possible for the moment (hope one day it will), you will still not go back in time to see what was there, you would see the present instead. Future is possible, past ain't. Nice video, but hard to understand for non english born.

Can you define time travel please? Is it possible for the same photon of light to hit my retina more than once if i can travel faster than light?

These videos are amazing! They're almost the only source I've found to give plain English explanations without the usual pop science hand-waving. A couple questions though - at the end of the video you turn around the conclusion and say that in fact such a path isn't possible. But such a path is what you would take traveling (virtually) faster than light, right? Does that mean that the Alcubierre drive isn't possible? Or is there a problem with the diagram? Do we need a special notation or transformation to describe what happens after the Paradox leaves Earth's light cone? What *would* the Paradox's world line look like? What would the Paradox's *reference frame* look like? I will be obsessively fretting over these questions while I wait for your answer :)

How to get rich with super-luminal speeds: Make a FTL-capable spaceship. Fill it with gold. Engage hyper-drive to arrive in your starting location 1 day ahead of when you were planning to leave. Now you have two spaceships filled with gold. repeat process until satisfaction is reached. Sell the gold. Profit.

Why this guy remind me of lord faarquad? Lol

I enjoy the logic in everything

I am so happy you guys remember the ansible

If I understand this properly then this serves as a proof by contradiction showing that FTL isn't possible. I'm wondering if this is a result of the math (ie the transformation not being made to handle this) or of the underlying physics.

You make two incompatible assumptions that cannot be both true : Assumption 1 (implicit): Einstein's 1905 constant-speed-of-light postulate is correct. Assumption 2 (explicit): Superluminal motion is possible. One of the assumptions is true, the other is false, and that's it. Causality, traveling back in time, etc. are irrelevant. In the example below, if the deactivation device is able to send a faster-than-light signal to the bomb, then special relativity ends up in a contradiction: the bomb explodes in the frame of the train but does not in the frame of the tunnel. We conclude that Einstein's constant-speed-of-light postulate is false and that is the end of the story: www.people.fas.harvard.edu/~djmorin/chap11.pdf pp. 41-42: "11.6. Train in a tunnel. A train and a tunnel both have proper lengths L. The train moves toward the tunnel at speed v. A bomb is located at the front of the train. The bomb is designed to explode when the front of the train passes the far end of the tunnel. A deactivation sensor is located at the back of the train. When the back of the train passes the near end of the tunnel, the sensor tells the bomb to disarm itself. Does the bomb explode?"