Rumor has it NASA
is actually working
on a real faster than
light warp drive.
So when do we get
our first starship?
Faster than light travel is
a staple of science fiction.
Star Trek warp drives
zip around the galaxy
at hundreds of times
the speed of light.
But traveling at the
real cosmic speed
limit of 1 times
the speed of light
would make for some
pretty dull sci-fi.
It would have taken
Han Solo 40 years
to make the Kessel
Run in 12 parsecs,
traveling at only light speed.
It's understandable that both
physicists and sci-fi fans
dream of cracking FTL travel.
Spanish physicist and
sci-fi fan Miguel Alcubierre
was so inspired by
the idea that he
decided that the Star Trek warp
drive should become a reality.
In fact, he was inspired by
Gene Roddenberry's choice
of the word "warp."
Alcubierre constructed
a warp field
in the mathematical language
of Einstein's theory
of general relativity,
a real solution
to the equations of
GR that would actually
allow faster than light travel.
Yep, pretty much the
ultimate in fan fiction.
But is it actually fiction?
NASA doesn't seem to think so.
It's Eagleworks
Laboratories is actually
trying to produce and
detect warp fields.
More on that later.
But if NASA's researching
it, it must be legit, right?
So when are we going to be
warping around the galaxy?
Let's break this idea apart.
First, it's important to
note that this idea does not
contradict the principle
of a cosmic speed limit.
That limit, the speed
of light, refers
to things-- mass,
energy, information--
traveling through space.
However, according to
general relativity,
there's no limit on the relative
speeds of two separate patches
of spacetime.
For example, as we talk
about in this episode,
the expansion of
the universe means
that very distant
galaxies are moving apart
from each other
faster than light,
even if the galaxies
are relatively still
in their local
frames of reference.
Also, below the event
horizon of a black hole,
spacetime cascades towards
the central singularity
faster than light, carrying
light, matter, monkeys,
and everything else with it.
Now, the spacetime around
and within a black hole
is predicted by solving
Einstein's field equations
around a point of extreme
positive energy density.
Basically, mass and energy
tell us how space should warp.
But if you're cheeky, you
can actually just make up
a solution to the
equations of GR
without starting with a real
mass/energy distribution.
That's what Alcubierre did.
He developed a spacetime
description, a metric tensor,
that describes a volume of
nice, flat spacetime enclosed
in a bubble of
extreme curvature,
a pinching or warping of
spacetime in the surrounding
shell that causes
space to expand behind
and contract in
front of the bubble.
As a result, the bubble is
pushed and pulled by spacetime
itself, moving at
speeds only limited
by the intensity of the warp.
A starship inside the bubble
is carried along for the ride
while feeling no
acceleration at all.
It's sort of like building a
conveyor belt out of spacetime.
You stand still with respect
to the conveyor belt,
but the belt itself
moves faster than light.
But is this even valid?
Can you just make up a
spacetime description
and then essentially solve
the Einstein equations
backwards to figure
out what arrangement
of matter and energy would
be needed to create it?
It's sort of like
giving the answer
before you have the question.
So, 42.
Yeah, sure you can do this.
There's just no guarantee
that the resulting mass/energy
distribution would be
physically meaningful.
In fact, when you try to
do this for the warp field,
you find that you
need to produce
a ring of negative
energy density in a band
around the ship to produce
the right warp bubble.
That means our ship looks
something like this in order
to produce a spacetime
curvature like this.
Unfortunately, it
may not even be
possible to make
negative energy densities
on large enough scales.
We can create something like
it, a negative pressure,
on quantum scales
via Casimir effect.
But on macroscopic
scales, you'd probably
need some sort of exotic
negative mass matter,
like element zero, which
is tricky, because there
may be no such thing.
There are other minor issues.
Any FTL device
can, in principle,
be used to make a time machine.
Excellent!
Except Stephen Hawking
chronology protection
conjecture states that quantum
mechanics will always stop
causality-breaking actions.
It suggests that
there's something
in the deeper union
of GR and quantum
mechanics, the
theory of everything,
that prohibits the warp drive.
One possible quantum disaster
is that the extreme spacetime
curvature of the
warp bubble walls
would roast the interior
with crazy Hawking radiation.
Does anyone else get the idea
that Stephen Hawking really
doesn't want us to
build time machines?
Suspicious.
Here's another challenge.
Assuming that you can even
make negative mass matter,
to make a warp field,
some of it would
need to go outside
the warp bubble, which
means it gets left behind
when you go to warp speed.
There are some proposed
solutions, one of which
is to lay down the
external negative energy
conditions along the path before
you leave, sort of like a warp
highway.
The first trip has to be
made at sub light speed.
But I'm personally cool with the
awesomeness of warp highways.
Last tricky thing--
as Alcubierre
devised the warp
bubble, he figured
it would take a lot
of negative energy.
In fact, it would take
significantly more negative
energy than there is
positive mass/energy
in the entire
observable universe.
Later refinements
brought this down
to the mass
equivalent of Jupiter.
Either way, not practical.
Happily, recent reworkings
of the bubble geometry
have cut this down further.
Thicken the walls
of the warp field,
and you get the negative
mass/energy requirement down
to the equivalent of maybe
the moon or even an asteroid.
Rapidly oscillate
the warp field,
and you hypothetically
soften the fabric
of space via higher
dimensional effects--
literally, a hyper
space warp drive.
And this brings mass
needed down to kilograms.
Given that we're just
making up solutions
to the Einstein
equations, we could even
shrink down the warp
bubble while expanding
the internal volume,
Tardis style, which
could get us down to
needing only milligrams
of negative mass.
If the bubble is small
enough, then we may not even
need actual exotic matter.
Quantum scale manipulation
of the vacuum energy
a la the Casimir
effect may be enough.
Check the description for the
sources of all of these ideas.
Now, this sort of wild optimism
has inspired NASA's Eagleworks
Laboratory to try an
experiment to create and detect
a warp field.
Now, this would be a field
created by positive, not
negative, energy density.
But baby steps, right?
It uses a Michelson
interferometer,
like a mini version
of the one being
used to detect
gravitational waves,
To measure the tiny changes in
path length created by a warp
field.
Now, some intriguing
results have been detected.
But interpretation is
very, very challenging.
So when are we going to be
warping around the galaxy?
If it's even possible,
it'll take several centuries
at a minimum.
As I've argued before,
we'll reach the stars
by sub light speed
starships long before that.
Even the Kugelblitz engine,
the black hole drive,
has fewer physics hurdles
than the warp drive.
Honestly, I think it's going to
take an actively interstellar,
or at least interplanetary,
human race to motivate
the monumental advancements
needed to build the first warp
drive.
The good news is we're going
to need a ton of physicists
to get to that point.
Let's make it so on the next
episode of "Space Time."
Last week, we talked
about gravitational waves,
and whether the advanced
LIGO Observatory has maybe
seen them.
You guys had lots of
amazing questions,
so let's get to them.
Renato Grigoli and others asked,
what about the LISA Mission?
LISA is amazing, although now
it's ELISA, the Evolved Laser
Interferometer Space Antenna.
It'll be an orbiting
gravitational wave observatory
designed to detect much higher
frequency gravitational waves
than advanced LIGO.
And this should actually
allow it to detect binary star
systems in our galaxy.
The program is being developed
by the European Space Agency.
NASA was originally
a part of it,
but had to drop out
due to funding cuts.
And so now, the original plan
is scaled back significantly.
Now, that seems a
shame, doesn't it?
The scheduled
launch date is 2034.
psantochi asks if we have
any comments on the BICEP 2
experiment.
OK.
So this was the much hyped
gravitational wave detection
based on polarization
anisotropies
in the cosmic microwave
background radiation that
came out earlier this year.
Yeah.
So now, the money is
on the signal actually
being due to dust, not G waves.
The lesson-- quadruple
check your quadrupole.
This is why LIGO
won't say anything
until at least the
end of the year.
Now, MrSh1pman wants to know,
if we find these G waves,
will it change anything?
Can we build something
cool with them?
Well, maybe.
Quantum mechanics began
as an abstract musing
on the nature of reality.
And I doubt that Max Planck
and Schrodinger and Bohr
imagined that this
crazy theory would
lead to the invention
of the transistor,
a quantum mechanical
device, let alone
the computer, the
smartphone, the Apple Watch.
Tenebrae wants our thoughts on
that amazing new Kepler Space
Telescope result
that the media is
hyping that there's an alien
megastructure eclipsing
a distance star.
Now, this is a stunning result.
But as we say on "Space Time,"
it's never aliens.
Check out the actual
signal that reveals
this eclipsing material.
Those dips are the drops
in the star's brightness
from some stuff moving
in front of the star.
It's dimmed by a crazy
20% at some points.
Now, this is definitely not
a clean geometric structure.
It looks like it has to be some
fragmented clumpy material,
like the proposed
swarm of comets.
That suggests a natural origin.
Although I imagine it could
possibly be insanely vast
ragtag colony of space
structures surrounding a parent
planet== except
it's never aliens.
Radio telescopes are
now pointed at it.
So perhaps we'll
know pretty soon.
To Un Disclosed,
I say, you laugh,
but the first
evidence of alien life
may be the
spectroscopic signature
of biogenetic atmospheric
methane on another world.
To Simon Martin, don't worry.
They're holding me very gently.
