So we had a poll on the channel for the next subject and concepts for Faster than Light
Travel and communication, FTL, also called superluminal technologies, got selected.
This turned out to be a problem though because as I began writing up material I found I was
quickly surpassing even the record holding videos for duration on this channel, Terraforming
Techniques and Solutions to the Fermi Paradox, both of which were surveys of concepts like
this was going to be, and I always felt involved a little too much skimming of the material,
and the latter comes in at nearly an hour.
On the other hand I’ve specifically been trying to keep the videos shorter these days,
and I just can’t imagine giving this subject a proper treatment in anything less than hour.
But a number of the concepts don’t require individual treatment and share a lot of common
properties.
So we’re going to break this up into sections and make a new series, like we have for megastructures
and habitable planets.
It also means I can turn out videos on other subjects in between new installments.
As we go through these we’re going to try to give all a fair treatment.
Our goal is to familiarize ourselves with these concepts regardless of whether they
work, and what we’ll see is that some can be outright dismissed whereas others work
but sometimes only because of possible scenarios requiring things like negative or imaginary
matter that we’re not sure even exists.
So today we’ll look at some of the basics of FTL, the misconceptions about the speed
of light a lot of people have, and one the currently most popular but also most misunderstood
FTL concept, Quantum Entanglement.
But before launching into that, I want to emphasize that since I usually try to avoid
including anything beyond simple algebra in these videos, and try to keep even that to
a minimum, while we can do Special Relativity with that, we can’t do General Relativity.
The Einstein Field Equations, the special solutions to which are what open the door
for a lot of these ideas, are simply out of our reach.
To look at that in any meaningful way you need the full series of calculus, linear algebra,
and both ordinary and partial differential equations.
Even with that, proper explanations take a very long while, more than I’m willing to
devote in this video or any other, but if you do have that mathematical background and
want to get that deeper understanding, I recommend Leonard Susskind’s 13-part lecture on General
Relativity and the video link will take you to that Playlist.
But we can talk about Special Relativity so let’s refresh on that real quick, we’ll
see if I can do it under three minutes.
Back in the late 1800s we noticed a peculiar property of light.
Which is that it always moved at the same speed.
Let’s illustrate this with Earth.
The sun constantly emits a lots of particles including photons, the particles of light.
If we have three people standing on the equator of Earth measuring these particles, not including
the photons, they will get three different speeds because the planet turns.
Here at noon, the man is neither getting closer or further away from the sun, so he measures
the particles at a certain speed, on average about 400 km/s for the solar wind.
But the Earth spins around at about half a kilometers a second.
So this guy near the dawn is heading right toward the sun at half a kilometer a second
and should measure those particles averaging about 400.5 km/s.
His speed combines with their speed, over here near the twilight the guy is flying away
from the sun and solar wind particles.
They need to catch up to him, and the particle speed measured will be 399.5 km/s.
That’s just good old-fashioned relativity, Galilean Relativity or Galilean Invariance.
Each of those three people has an inertial frame of reference, which is to say they have
a speed and direction, and each will measure any object’s speed and direction differently.
Same as you aren’t moving when sitting on a bus, but see a guy walking up the aisle
of the bus as moving, while someone outside the bus will see you and the guy in the aisle
both moving with the addition of the speed of the bus.
Back to our Earth model, these guys are measuring the incoming particles at different speeds,
but now they start measuring light, incoming photons, and something weird happens.
They all measure it at the same speed.
Why doesn’t matter yet.
That was just the state of play at the dawn of the 20th century.
Light, for whatever reason, always had the same speed when measured.
That’s not a consequence of Einstein’s Special Relativity, it’s the strange fact
he developed the theory to handle.
He assumed, postulated, only two things.
That the laws of physics were invariant in all inertial frames, which just means the
speed and direction you are moving at doesn’t change the rules of the Universe, and that
the speed of light is the same for all observers.
It does not vary, it is invariant.
Since speed is simply distance over time, 60 miles, a distance, per hour, a time, if
people going different speeds are measuring something and getting it’s speed the same
then the Einstein reasoned that these observers had to measuring different distances and times.
And he further reasoned this effect wasn’t just limited to light but to anything traveling
fast, the closer to the speed of light, the more intense the effect, as governed by this
equation.
And we’ve checked this, I don’t think there’s any theory that’s been checked
more often and rigorously.
So if a guy standing on a giant digital space clock measures that clock as a mile long and
checks his watch, he’ll see them running at the same speed.
If a guy flies by at 87% of the speed of light, he’ll see that clock only seems to add a
second every other second and the clock will only be half a mile long to him.
Another guy flying by at 97% of light speed will see the clock running at only a quarter
as fast as his watch and will measure the clock as only a quarter mile long.
All right, refresher complete, intro complete.
I mentioned misconceptions.
The first of these is the speed of light itself.
It really isn’t about light at all, it just happens to be one of the few things that travels
at that speed and the one we first discovered.
Any massless particle, such as the gluons that glue quarks together, moves at the speed
of light, and nearly massless particles like neutrinos usually move within spitting distance
of it.
It’s even possible photons themselves have a tiny little bit of mass and actually move
just a hair under the speed of light, though of course if that were so we’d have to chuck
speed of light as a term.
But that would be fine, since it’s more accurate to think of this as the maximum speed
information can move at, because that’s the actual restraint that matters.
Nobody’s going to rename it the speed of information, or the maximum propagation rate
of cause and effect, but that’s more accurate and more appropriate to what we really want
to circumvent anyway.
We don’t really care if photons get somewhere faster, we care about the signal we are transmitting
with those photons.
And information in this context include objects since a note, or a person, can obviously contain
information.
The second misconception is that if something is some number of light years away, say a
hundred, you can’t get there in under a hundred years.
That isn’t so, you could get there in a second flat if you had enough energy to get
really close to light speed.
When you got there though, while only a second would have passed for you, because of time
dilation, their calendar will say it’s a hundred years in the future.
The third misconception is that relativity says nothing can go faster than light, that’s
never been true or claimed.
It’s trivially simple to move something faster than light and the only reason you
can’t easily verify this yourself is that you’d need a strong telescope and a very
powerful laser to do it.
If you stuck a beam on the edge of Mars, and then flicked it as quick as you could across
the surface to the other end, someone watching that beam will see it swipe across Mars very
quickly and faster than light can travel.
In this same way, if you moved something in front of a light source you could get its
shadow to move faster than light.
That beam, and that shadow, are things.
This not a quibble, because it’s important to a lot of misreported violations of light
speed.
Nor is it fringe science or radical thinking, this is universally accepted and mundane science,
and it matters because while you can argue the dot and the shadow aren’t real objects,
we have a lot of stuff like virtual particles and wave packets that can also do this trick
and also have that ethereal status as not exactly real.
But what matters is that you couldn’t use that to send information faster than light.
That light dot on Mars will move faster than light but it won’t move when your hand did,
it will move when the light from that laser in your hand arrives.
Same for a shadow, it won’t move until the light you’re blocking, or no longer blocking,
arrives.
Stick something right in front of the sun shadowing Earth and that won’t appear for
several minutes.
And again this is an important distinction because there are other examples of things
that move faster than light, or that we have some good cause to think can, and in virtually
all of these we can show how you couldn’t use it to transmit meaningful information
faster than light.
But you’ll probably have seen articles in pop-sci publications loudly proclaiming that
something does move faster than light and simply assuming you can use that to send information,
when in most cases they’ve been outright told by the very person who discovered the
item that it does no such thing.
We see this lot with things involving quantum, which leads us to Quantum Entanglement.
Since sometimes in the mid 70s to about the turn of the century the Tachyon, which we’ll
cover in the future, was the got to particle for science fiction trying to justify their
in-story mode of faster than light travel.
Sometimes in the early 2000s that role got stolen by Quantum Entanglement.
That’s actually kind of funny since Entanglement has been around as an established idea since
the 1930s but tachyons came up as an idea in the 60s.
Quantum Entanglement, leaving out the math, isn’t too complex.
Though the feature that tends to be of interest to people in sci-fi for faster than light
communication is actually Quantum Non-Locality, what Einstein famously called ‘spooky action
at a distance’.
But Quantum Entanglement is a situation in which two or more particles are connected
in terms of their quantum state.
They are entangled.
You can’t describe individual parts of the system of two or more particles independently
and correctly.
Distance doesn’t appear to matter for this, and the most common entangled state discussed
in this would be two particles being created by some event and flying away.
So you’ve got two particles flying away from each other, and being quantum thingies
that whole Schrodinger’s Cat issue comes into play where you not only don’t know
what the properties of that particle are until you measure it but we’re pretty sure it
isn’t even determined until you do.
Now these properties can be anything from spin to charge to momentum and many other
but for now I’m going to call these coinons and say they have the property of being either
heads or tails, and when made in pairs one must be heads and the other tails.
What Quantum is telling us is that observing a coinon is equivalent to flipping and catching
it, until then its spinning around and doesn’t have a heads state or a tails state, it’s
both at once.
The moment I catch that though the other coinon turns into the opposite.
I catch a heads and a moment later my lab partner catches the other particle and sees
its on tails.
We’ve checked this tons of times and as best as we can tell it is true, and can only
happen if those two coinons are talking to each other somehow.
And while we haven’t determined yet if this is actually instantaneous we have nailed this
chat down as taking place at no less than 10,000 times the speed of light.
This is actually Quantum Non-Locality, which as the name implies indicates the ability
of Quantum things to act in a way which would imply they violate Locality, or basically
means they can do things faster than the speed of light, or appear to anyway.
The coins, pardon, coinons, are entangled, once one is determined the other is determined.
And it doesn’t have to be just one particle, we’ve done this with larger things like
molecules, and hypothetically at least you could do it with a person.
Now, obviously your first thought is that you can use this for sending information faster
than light.
But you can’t, or at least you can’t by any method we know.
I think people get hung up on the super-fast motion and figure that must be able to be
tapped but remember we already saw to superluminal effects with our Martian Laser Dot and Shadow
and we know you can’t send information with either, at least not faster than light, and
you can’t with Quantum Entanglement or Non-Locality either.
Here’s why not, and we will just use coins here.
I am giving you a coin and your buddy a coin, a magic pair of entangled coins, and I am
telling you that no matter how far away you are the moment you flip your coin his will
flip to the opposite side yours comes out on.
But this is a truly random coin, you have to flip it, you can’t just set it on the
side you want.
Remember this a quantum random event, and it has a 50/50 chance to come up heads or
tails.
How do you send a message with that?
I mean if we could control the coin we could easily send a binary code, heads one, tails
zero.
Too easy.
All you’re going to generate is random noise though.
Heck, quantum randomness like this is one of the few safe ways to generate a truly unbreakable
one-time pad encryption since there will be no pattern to the result.
But wait, you can send a message using that coin.
I don’t need my distant partner to receive heads or tails, I just need him to know I
flipped the coin.
I decide I will flip or not flip the coin once every second, a coin flip, regardless
of outcome, it’s a one, and a non-flip is a zero, a simple binary code with a bandwidth
of one bit per second.
Again too easy.
Our digit are simply motion or non-motion.
Unfortunately, once again, that doesn’t work.
Because with quantum particles you have no way of knowing if your particle has or hasn’t
been observed when you look at it.
It works for our magical coin but not for entangled particles.
I can’t send out a constant beam to distant locations from some central location that
they can then use to transmit information superluminally, or have two big boxes full
of entangle particles pairs they can check at need to send messages, because the state
of each particle isn’t determined until you look at it and you don’t actually know
if it’s partner has been looked at unless someone tells you, by old fashioned light
speed.
You can both meet up later, or phone each other, and tell each other which once you
looked at and what it was and note that his was opposite yours but you can’t send any
information this way.
This doesn’t necessarily mean we’ll never figure out a trick for using this, since these
particles appear to be talking faster than light they presumably use a method that maybe
we can use too.
But for now this method is closed off to us and doesn’t appear to have any way we could
use it.
Next time in the FTL series we’ll take our first look at Exotic Matter and its role in
FTL technologies by looking at Tachyons, a hypothetical type of particle that not only
goes faster than light but actual goes backward in time, and we’ll discuss the implications
and dilemmas of that.
If you enjoyed the video like it and share it, questions and comments are welcome, and
if you want to be alerted when that video comes out, click the subscribe button, and
in the meantime you can try out one of these other playlists.
Thanks for watching and we’ll see you next time.