
Scientists Are Starting to Take Warp Drives Seriously - elorant
https://www.sciencealert.com/scientists-are-starting-to-take-warp-drives-seriously-especially-this-one-concept
======
mellosouls
_Scientists Are Starting to Take Warp Drives Seriously_

No they aren't. This is just a fluff piece for a highly speculative but
excitingly sci-fi sounding propulsion mechanism with not even the remotest
prospect of practical implementation. See also EM Drive, etc.

~~~
hhas01
Never mind implementation; what about causality?

[https://en.wikipedia.org/wiki/Causality_(physics)](https://en.wikipedia.org/wiki/Causality_\(physics\))

Anyone who wants to build a warp drive has to start by proving Einstein wrong.
Anything else is a scam.

~~~
alfromspace
How does FTL violate causality? I've tried reading on it before but didn't
understand it with my casual understanding of physics.

~~~
shadowgovt
This website explains it much better than I can, but the tl;dr explanation is
there's no "privileged frame of reference" in relativity. Even if two frames
of reference can be arranged to agree on a causal sequence involving FTL
phenomena, a third observer can be constructed that perceives the sequence of
events happening out of order; they get the light from effect before they get
the light from cause.

This creates nasty phenomena that we don't seem to observe in nature (i.e. if
the third party observes effect before cause, they can interfere with cause.
Everyone loves a good temporal paradox ;) ).

[http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-
ti...](http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel)

~~~
alfromspace
>What does the ship see? They see the phone call received on Proxima Centauri.
Then they see the phone call placed from Earth. Effect precedes cause:
causality is violated. In fact, if the ship had a FTL phone set up in the
right way, they could call Earth before Earth placed the call. They could even
tell Earth "hey, don't make that call to Proxima Centauri we just saw you
make." Then what?

I don't understand the problem here. The ship couldn't call Earth before Earth
placed the call. It would see the call being received before Earth placing the
call, but if it then called up Earth on their FTL phone and said "hey, don't
make that call to Proxima Centauri we just saw you make," wouldn't Earth just
reply "Uh, we already made the call, you seeing old light doesn't mean these
events didn't already happen." Why does it matter what the third observer
sees? Cause and effect aren't violated just because it can appear that way.

~~~
shadowgovt
"just because it can appear that way" is all "cause and effect" are.

The source doesn't do the math on the final step, but you can arrange the
third observer so they emit light that reaches Earth before the phone call is
sent (because we are assuming FTL tech).

~~~
alfromspace
Then it doesn't violate any fundamental laws of existence, does it? We're just
talking about receiving delayed images of events. The ship isn't engaging in
backwards time travel by contacting Earth after seeing its call being
received, because Earth knows it already placed the call. No information from
the future is being conveyed to Earth, and the third party isn't actually able
to affect the "cause" after seeing the "effect", because the cause is over and
done with.

~~~
shadowgovt
No, you misunderstand me. Earth hasn't placed the call yet; the ship can use
FTL and its knowledge of the effect to send a message to Earth that Earth
receives before it places the call. The scenario you're describing is
described as such in the link above:

"""

Now, you might say "wait, light takes a finite amount of time to travel.
You've just shown what times the spaceship will assign to various events, but
they can't see it immediately. That'll save us!" Sadly no. Here's when the
ship actually gets the light from the events. [complicated figure, but it
shows there's enough time in the light-cone chart for the ship to receive the
'Proxima received the phone call' event and then travel to Earth slower than
speed of light and tap Earth on the shoulder before the phone call was sent]

As you can see, the light from the phone call reception arrives well before
the light from the placing of the phone call. Again: causality is violated.

"""

In fact, that message can be "Place the call," which means the call is placed
because Earth was told to by the third party because the third party knew the
call had to be placed because they observed the effect because the call was
placed... FTL allows for closed-causal loops.

~~~
alfromspace
I'm still not getting it. What mechanism allows for knowledge of the effect
before the cause objectively happens? For the third party to observe the
effect, the cause had to have happened from Earth's perspective. The fact that
the light hasn't reached the third party yet seems immaterial. I'm not trying
to play gotcha, seriously don't get it.

"As you can see, the light from the phone call reception arrives well before
the light from the placing of the phone call. Again: causality is violated."

It's still only speaking about the perspective of the ship, and it seeing
effect before cause.

~~~
shadowgovt
> What mechanism allows for knowledge of the effect before the cause
> objectively happens?

Yeah, it's tough. I don't think I can explain it without bootstrapping a
college semester of relativistic physics, and I'm afraid I'm not that good. :(

To start your search, "Objectively happens" is the intuition that doesn't hold
water in relativity. There is no objective frame of reference (i.e. nothing in
the universe is moving at 'speed zero', or more precisely, _everything_ moves
at 'speed zero' relative to itself). So everything is relative; there's no
place anyone can stand and observe things objectively. Relativity changes the
rules upon which reality operates so they hinge, loosely, on two fundamentals:

1) The speed of light, in a vacuum, must be observed to be the same by all
observers

2) Observers do not agree on the times that they measure for when events
occurred (for example, the "moving train" thought experiment shows that
simultaneity is violated by relativity), but they can agree that the events
align to each other subject to the Lorentz transformation when relative
velocities are accounted for.

Under these rules, causality is maintained; I don't have the whole proof at my
fingertips, but it can be shown that regardless of how you apply Lorentz
transforms to sublight-velocity observers, they'll agree that events that
caused one another have the same ordering (this is a subtlely different
statement than "Two things happened at the same time," and it's partially a
property of the events that are effects being within the 'light cones' of the
effects that are causal). FTL travel allows one to exceed the "light-cone
limit" and as a result, the causality constraint that 'effects are in the
light cones of causes' is violated. The frame of reference where one event
caused the other exists (i.e. there are velocities one could have where the
light cones will line up that way), but there are also now velocities one can
have where the light cones do not line up that way. It's only impossible for
_any_ observer to see effects happen before their causes if nothing can exceed
light-speed.

For your specific question ("What mechanism allows for knowledge of the effect
before the cause objectively happens?"), I think I can offer a short
hypothetical thought experiment that might illuminate things. Imagine there
were a door from Earth to Mars allowing instantaneous transit (so infinite
velocity, in excess of speed of light). One day, the sun blinks out of
existence. Earth will see this occur three light-minutes before Mars does.
Someone steps through the door and yells "People of Mars! I come with a
warning! In three minutes, the sun will go out! Evacuate now!"

From the Martian point of view, that person is a time traveler from the
future, and the intuition relativity brings to us is that the Martian point of
view is as "objective" as any other point of view. This (Lorentz-transform-
violating) visitor has knowledge of an event that will definitely occur in
three minutes before the cause of that knowledge has occurred.

------
contravariant
I think it's always been taken somewhat seriously from the start of general
relativity (it didn't take long before the first formal description of a
wormhole). The discovery of gravitational waves has again provided strong
proof in favour of general relativity, but I don't think this is what is
preventing people from seriously considering warp drives.

Until a way is found to remove the need for exotic matter or to generate
exotic matter it remains a purely theoretical exercise.

~~~
qubex
The problem isn’t really the need for exotic matter in enormous quantities
(apparently we have a negatively curved universe where dark energy serves
exactly that purpose), but rather the aspect of causal disconnection:
everything inside the bubble is disconnected from everything outside it, so
it’s difficult to envision how the spacecraft inside could be generating,
steering, or even shutting down the warp bubble outside itself.

------
unknownkadath
I feel really bad for this undergrad; The student's advisor did not do him any
favors by letting him go and give this talk to the IEEE. It is perfect
material for clickbait farms and the wider krank-net.

If you can access it, the doi link to the conference paper is:
doi.org/10.2514/6.2019-4288

This is not a serious attempt, and in no way indicates that scientists are
starting to "take warp drives seriously." It is pitching that same silly stuff
White et al have been promising is "real close now" for around 15 years. I
also cringed at the equations and figures that were obviously copy/pasted from
White's PDFs to Word and back.

Having this kind of kooky thing hanging from a baby undergraduate's name--a
name that I'm not going to propagate on the web for his own good--is not going
to help his future career, and everyone involved should feel bad for wasting
his time. Sorry this is boiling my grits so badly, am I over reacting or is
this awful?

------
honoredb
Typo near the beginning, "press a petal," gave me a fascinating mental image
for a second.

I'm sure it'll be informative to learn exactly why every theoretical avenue
for faster-than-light travel doesn't work, but I feel like we can infer from
the size of the universe that these effects don't exist; if they did, they'd
dominate our observations of the universe and we'd never have thought the
speed of light was a fundamental limit in the first place.

~~~
nateferrero
Flower petals would make an amazing tactile controller

------
tjchear
I've heard often about how the energy estimate for warp drive has been revised
down from the mass of the universe to that of Jupiter. Forgive my ignorance,
but is this just a matter of refining the shape of the warp around a
spaceship, or is it something else? What would it take to further drive down
that theoretical energy requirement? Is there a trade-off being considered
here?

~~~
qubex
It is the result of refining the geometry of the warp bubble to be generated
by two toroids rather than a single ring, inflating the interior compared to
the external perception thereof (a la Tardis), and most critically, by
oscillating the field.

------
diegoperini
"Scientists" is not single community of converging opinions. "Scientists" do
not even agree on how serious the climate change is. Prefixing these kind of
titles with "Some" (as in "Some Scientists...") may seem redundant but it
actually gives an entirely different message which I believe is almost always
important to be explicit about.

------
reportgunner
If you like the idea of Alcubierre Drive, give Elite: Dangerous a try - every
ship (that is not a fighter) has an Alcubierre Drive installed and you use it
extensively to get around "The bubble" (a sphere of inhabited space roughly 20
light years with Earth as its centre) and even beyond.

I have no affiliation with Elite: Dangerous, that's just how I learned about
Alcubierre Drive

------
34679
>Please don't post shallow dismissals, especially of other people's work. A
good critical comment teaches us something.

[https://news.ycombinator.com/newsguidelines.html](https://news.ycombinator.com/newsguidelines.html)

Just a reminder.

------
mnky9800n
sciencealert is starting to post non-clickbait articles. wait no they aren't.
lol.

------
pingyong
tldr: Nothing changed, we still don't know if negative energy is even
something we can generate.

~~~
Pigo
But they got it down to only needing the total negative energy requirement to
be around the mass of Jupiter. So we're on our way?

~~~
jerf
That's one way of looking at it. No sarcasm, I'm serious.

But another valid way of looking at it is that scientists have moved it from
"impossible", to "impossible", to "impossible", then, with some more work,
upgraded it to "impossible". Or, in other words, no progress at all.

The negative mass is still only one problem with the Alcubierre drive concept.
Last I knew, it remains unclear how to enter and/or create a bubble without
being totally destroyed, or exit and/or destroy a bubble without being totally
destroyed. Reuse of any of the components is probably also a problem; in the
Einstein equations, playing fancy games with spacetime tends to want to rather
explosively go back to normal with the entire mass-energy of the distortions
in question. It's also somewhat unclear what would happen to an Alcubierre
warp drive in the real universe, where the space between stars is not a
perfect vacuum.

It's not a drive being taken "increasingly seriously", unless you mean it's
gone from epsilon to twice epsilon. It's a particular solution of the Einstein
equations that involves impossible quantities of things and a particularly
complicated setup basically already existing. If we didn't have science
fiction making FTL drives cognitively available to people's imaginations and
perhaps even subconsiously bleeding over into people's impressions of what
real is (i.e., the bizarre but clearly pervasive subconscious assumption that
seeing something in a sci-fi show means the probability of that occuring in
real life is higher), nobody would be taking this seriously right now. Between
the actively impossible elements (sustained, enormous quantities of negative
mass) and the things that may not be mathematically "impossible" but are
probably engineering-impossible, this is just a thought experiment right now.

Now, for all that, it's a worthy thought experiment. I am a firm believer in
putting down a bit of money on the very long-shot payoff research. I'm not
asking anyone to stop working on it. I'm just asking for realistic assessments
of the current state of the art, which is that the probability that this drive
will ever work is basically indistinguishable from zero at this point.

~~~
ColanR
> But another valid way of looking at it is that scientists have moved it from
> "impossible", to "impossible", to "impossible", then, with some more work,
> upgraded it to "impossible".

I think that description used to apply to a lot of technology, which then
progressed to "almost impossible", "slightly less impossible", and finally to
"built a prototype". From my laymans' perspective, it's the trajectory that
matters more than the current state-of-the-art.

~~~
jerf
Not the way I'm using the word. The drive is not currently merely like an
airplane, where it is obviously possible to fly (at least as well as birds),
we just didn't know how to bang the rocks together correctly to do it. The
Alcubierre drives requires things that we have every reason to believe are
_impossible_. In English the term "negative mass" may just seem like, oh,
someday maybe we'll advance and have this; in math, it's even worse than you
may think I'm going to say. It isn't that we don't know what "negative mass"
is. It in fact already appears in some of our equations. The problem is that
the product of negative mass times the amount of time it exists seems to be
fairly sharply bounded at literally dozens of orders of magnitude too small to
conceivably be of any use.

We have every reason to believe that stable negative mass is impossible. Not
just "we don't know how to do it yet", but _impossible_. Impossible is like
"perfect"; technically, it doesn't admit of "degrees" of impossible. So moving
from "impossible" to "impossible" is not progress.

People like to cite a lot of cases of various supposed boundaries being broken
over time as evidence that maybe this one will be broken too, but there's a
qualitative difference between some "elderly distinguished scientist" opining
something is impossible, and the mathematics of physics saying something is
impossible. It is not a sophisticated, open-minded position about the
technological possibilities of the future to say that someday, man will break
the barriers of the laws of thermodynamics and someday produce the perpetual
motion machine; it is ignorance and scientific illiteracy. FTL is not _quite_
that certain yet, but at the moment, the smart money is on it being the exact
same sort of thing, not humanity someday overcoming it. At the moment I'd say
that if you properly understand the science of the matter and just how
thoroughly reality seems to stymie us in our every attempt to worm around the
speed of light restriction, you are completely unjustified in giving even a
.1% chance of FTL being possible, let alone that humanity will ever achieve
it. It looks to be a lot closer to perpetual motion than breaking the sound
"barrier", which barely even deserves the same English word as the speed of
light barrier given their massive qualitative differences.

Now, as I say, the long shots sometimes pay off, so I don't advocate that
nobody thinks about this. Even the process of discovering why the <.1% is
better thought of as a flat 0% can be valuable scientific progress, plus there
is always the chance I'm wrong. However, at the moment, it looks like FTL is a
problem that is far harder than just waving a couple of hoary old quotes about
scientists at it is going to solve. You're not fighting "scientists", but the
_math_.

Personally, I tend to think Hawking probably got it right with his chronology
protection conjecture, and that even if you do manage to build something that
goes faster than light or travels back in time, the entire system will
literally explode. FTL may not be just impossible because we don't know how to
build it, but because it really is fundamentally impossible; spacetime will
_literally_ explode in your face even if you do manage it.

[https://en.wikipedia.org/wiki/Chronology_protection_conjectu...](https://en.wikipedia.org/wiki/Chronology_protection_conjecture)

~~~
ColanR
> The drive is not currently merely like an airplane, where it is obviously
> possible to fly (at least as well as birds), we just didn't know how to bang
> the rocks together correctly to do it.

> People like to cite a lot of cases of various supposed boundaries being
> broken over time as evidence that maybe this one will be broken too, but
> there's a qualitative difference between some "elderly distinguished
> scientist" opining something is impossible, and the mathematics of physics
> saying something is impossible.

I appreciate your distinction in the use of the word 'impossible'. I didn't
actually see what you meant by it before. From what I remember from learning
about the development of airplanes, it was considered physically impossible
until proven otherwise. It wasn't an elderly scientist saying planes can't
fly, it was the best science of the day declaring that something heavier than
air was meant to stay on the ground (IIRC).

I'm simply skeptical of claims of impossibility, across the board. I do
appreciate and understand the science of the reasoning behind the claim; but
to a layman who knows a bit of the history of science, 21st century scientists
declaring things scientifically impossible (because science has progressed so
far since 100 years prior) sound eerily similiar to 19th and 18th century
scientists saying the same thing, for the same reason.

~~~
antepodius
I have a very hard time believing that, given birds existed.

------
ptah
how is this different from aether
[https://en.wikipedia.org/wiki/Aether_theories](https://en.wikipedia.org/wiki/Aether_theories)

~~~
juped
Using "aether" as a generalized snarl word is really irksome. None of us were
alive for the debates in physics of a century ago. General relativity is an
aether theory; i.e., it ascribes properties (the metric tensor) to empty
space. Appeal to authority below since that's the level we're playing on when
we misuse dated terminology like this.

"We may say that according to the general theory of relativity space is
endowed with physical qualities; in this sense, therefore, there exists an
ether. According to the general theory of relativity space without ether is
unthinkable; for in such space there not only would be no propagation of
light, but also no possibility of existence for standards of space and time
(measuring-rods and clocks), nor therefore any space-time intervals in the
physical sense."

\-- Albert Einstein

~~~
taylodl
Don't confuse the model with reality. The interesting thing about GR and its
stress-energy tensor is you _can 't distinguish_ the model from the reality.
The model says space is curved and it's this curvature which we perceive as
gravity. Does that mean space is actually curved? No. But we have no way to
tell. It's a fascinating concept when you think about it.

Quantum gravity may give us a way out but so far we've achieved little
progress, mainly due to the very same stress-energy tensor being a different
type than those found in other quantum fields. Viktor Roth provides a simple
explanation of the problem:
[https://www.forbes.com/sites/quora/2017/05/17/the-
marriage-o...](https://www.forbes.com/sites/quora/2017/05/17/the-marriage-of-
einsteins-theory-of-relativity-and-quantum-physics-depends-on-the-pull-of-
gravity/#65399968e3a6). If you're into physics Viktor is a fun guy to follow
on Quora.

------
Vysero
Sounds to me like they are discussing tech that may exist 5 to 6 hundred years
from now... not really worthy of their attention imo.

~~~
pluto9
For it to exist 500 years from now, someone will have to work on it for the
next 500 years.

~~~
Vysero
That's not true. What it would take is a massive advance in material science
or what-have-you. Once that massive advance happens then it may or may not
make this tech possible. However, that massive advance will most likely have
nothing to do with working on this particular tech in the meantime.

