
Humanly Traversable Wormholes - apsec112
https://arxiv.org/abs/2008.06618
======
andyljones
Did a double-take seeing Maldacena's name on this. He's better known for
discovering AdS/CFT, which is the foundation of a _lot_ of modern work on
quantum gravity.

[https://en.wikipedia.org/wiki/AdS/CFT_correspondence](https://en.wikipedia.org/wiki/AdS/CFT_correspondence)

------
Analemma_
> An even bigger problem seems to be producing the wormhole in the first
> place. It would be interesting to understand whether they can be produced in
> the RS model. Since they require topology change, this seems difficult.

Has there been any serious (or at least semi-serious) thought given to this?
I've perused some literature on wormholes, and it seems like even if you can
somehow handwave away the GR energy conditions, the causality violations,
etc., when talking about wormholes, everyone's always stuck on the issue of
getting one to begin with. Do we know anything about whether the topology of
spacetime can be changed?

~~~
zamalek
So far as changing the topology of spacetime, NASA is (or was) investigating
it as part of Alcubierre/Warp drive research[1]. That being said, a warp
bubble is a far simpler goal than a wormhole.

> According to White, these results showed a vanishing but non-zero difference
> between charged and uncharged states after signal processing, but this
> difference remains inconclusive due to external interference and limits in
> the computational processing.

[1]: [https://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-
field...](https://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-
field_interferometer)

~~~
enchiridion
Isn't that changing the geometry, not the topology?

------
dimastopel
Would a wormhole enable escaping our local group, in theory? From what I
understand the current assumption is that we will never be able to travel
beyond our local group because of the accelerated universe expansion.

~~~
raducu
If the wormhole is somehow artificially made, no, because, as far as I
understand, you have to drag the exit hole through space, and thus you are
limited by the speed of light.

As to naturally occurring wormhole, I don't think there is any accepted and
likely ocurring phenomenon that creates a wormhole, let alone across galaxies.

So most likely, no.

~~~
simonh
The only example I can think of is a wormhole created by quantum fluctuations
in the early universe, stabilised by a negative energy cosmic string, then
cosmic inflation expanded it to macroscopic size and flung the two ends far
apart. But of course the various features of that aren't universally accepted
and are not likely to occur, so eh.

------
qubex
It’s pretty clear why we’re all fascinated with faster than light travel (it
makes the Universe feel accessible on our comparatively tiny timescales), but
it’s also a sheer display of narrative obstinacy on our part that we continue
to try to find loopholes in the rules of the Universe to allow something that
so patently ain’t meant to be.

Just build ‘em dormant A.I. probes, set ‘em off on their long lonely drifts,
and let the magic of self-reproducing Von Neumann automata take hold once they
arrive in a star system with suitable resources!

~~~
aeternum
Unfortunately probes just don't capture the human imagination like manned
exploration does.

Perhaps a reason to invest in tech like neuralink? If we eventually merge with
AI, perhaps each of those probes will ultimately feel like an appendage that
is just slow to respond.

~~~
boxed
I disagree.
[http://localroger.com/k5host/pitv.html](http://localroger.com/k5host/pitv.html)

I have re read that dozens of times. It's a striking and powerful vision of a
possible future.

~~~
aeternum
So the machines put them on a barren planet in the middle of interstellar
space with no source of natural light? Seems like a pretty desolate end for
humanity.

I'd rather merge my consciousness with the probes and explore, something like
this:
[http://www.skyhunter.com/marcs/GentleSeduction.html](http://www.skyhunter.com/marcs/GentleSeduction.html)

~~~
boxed
Home is home. But keep reading for more :)

------
newsbinator
I was curious how we'd go about detecting wormholes:

[https://www.sciencedaily.com/releases/2019/10/191023135913.h...](https://www.sciencedaily.com/releases/2019/10/191023135913.htm)

> In the new paper, scientists write that if a wormhole does exist at
> Sagittarius A _, nearby stars would be influenced by the gravity of stars at
> the other end of the passage. As a result, it would be possible to detect
> the presence of a wormhole by searching for small deviations in the expected
> orbit of stars near Sagittarius A_.

I assume that would be a rather large worm hole, for us to detect the
gravitational effects on stars that exist on the other side.

I wonder if there's any approach to detecting micro-wormholes closer to our
own star? Perhaps by setting up tens of thousands of micro-satellites around
(Starlink), blasting radio waves in all directions, and seeing which ones
don't make it to the receiver?

~~~
Akronymus
> I assume that would be a rather large worm hole, for us to detect the
> gravitational effects on stars that exist on the other side.

Would the size of the wormhole actually affect the amount of gravity bleeding
through? And how do we even define the size of a wormhole?

~~~
Teever
Perhaps we could measure it by the amount of gravity bleed through.

~~~
Akronymus
That....

makes entirely too much sense. Altough, I still would question the validity of
it, because in cases where there could be VASTLY different masses on the other
end. So, the bleed through would only really give an indication of the gravity
well on the other side.

All just from my knowledge which is VERY limited.

~~~
Teever
Yeah, I thought of that after I replied to your comment and I guess you'd have
to use some standard mass located a standard distance.

I'd imagine a unit people would use would be the gravitational force exerted
by an object the size/mass of the sun located 1 AU away from the wormhole.
Though I imagine there would be some more fundamental unit for measuring this
kind of thing.

------
imglorp
If there are any naturally occurring wormholes, would they have different
external properties as compared to black holes?

~~~
yazaddaruvala
At the least light should escape a wormhole, and we should "see" what is on
the other side. Otherwise I'm not sure how it'd be possible to detect any
difference between a wormhole and a blackhole.

~~~
gizmo686
Thats the question. Even if wormholes exist, the Universe is under no
obligation to make them observable to us. If they are always on the other side
of a black hole event horizon, then there would be no way for us to detect
them, even in principle.

~~~
maxcan
It is true no physical law obligates the universe to make them observable to
us. But, this is the same universe that gave rise to Star Trek, Firefly, and
especially The Expanse making so many of us dream of interstellar travel. So,
I’d say ethically it’s pretty damn obligated to make them observable :)

/s (Sort of.. not really)

~~~
iso947
Firefly is all STL. It’s ambiguous how they got to the system they now occupy.

~~~
Filligree
Wait, really? I haven't watched the show, but aren't there like six different
habitable planets involved?

You can't have that all in a single star system.

~~~
AnIdiotOnTheNet
They kinda try to patch it up in the movie "Serenity". Supposedly the whole
show takes place in a gigantic star system full of giants with dozens of moons
amounting to hundreds of worlds. They also have some form of terraforming tech
to make inhospitable worlds habitable.

Frankly I find that whole set up only slightly more plausible than some kind
of FTL, especially since they also have gravity manipulation tech already.

------
wrkronmiller
> Using them, one could travel in less than a second between distant points in
> our galaxy. A second for the observer that goes through the wormhole. It
> would be tens of thousands of years for somebody looking from the outside.

Unless the energy requirements are lower, it sounds like this isn't much
better than just traveling close to c (assuming you had adequate shielding).

~~~
Filligree
However, with a wormhole you can _step back through it_.

Which, yes, in this case would send you back in time. No problems there; it
isn't a causal loop.

~~~
bollu
Not sure I understand, why is it not a causal loop?

~~~
Filligree
The wormhole sends you back in time, but not far enough back to arrive at your
point of origin before you left.

If you could treat the wormhole like a magic door that takes you across space,
then two people looking at each other through the door wouldn't see anything
unusual. One would be in the distant future, by the galaxy's clock, but not by
the wormhole's.

So going through in one direction takes you into the future, and the other
takes you into the past, but it's a constant offset. The size of the offset
depends on how you moved the other end to where it is.

It's true that with multiple wormholes you could try to create a loop, though.
That would probably fail due to virtual particular loops.

------
kklisura
> Interestingly, they are allowed in the quantum theory, but with one catch,
> the time it takes to go through the wormhole should be longer than the time
> it takes to travel between the two mouths on the outside[a]

> [a] This also implies that they can not be converted into time machines

This doesn't seem like "classical" wormhole, right?

~~~
JoachimS
But it could still be useful. As a source of energy, propulson for example.
Sink one end into a star and put the other where you need power.

~~~
samus
If the wormhole travels all the way to the core, then it will relocate about
half of the star to the other end. If the wormhole can be closed, then it
would act as a giant pizza cutter for stars. Potentially very useful to defuse
supernovas. Or to utterly annihilate your enemy's stronghold...

What would happen is more complicated to answer if the wormhole stays open.
The star would effectively have double the surface area, but apart from that,
the consequences for the star's future development elude me right now.

------
m_a_g
Any suggestions on what to learn so that I can understand this paper? I would
love to be able to fully comprehend this paper.

~~~
messe
The following assumes you are comfortable with Linear Algebra, Calculus, and
Basic Physics (Newtonian Mechanics and Thermodynamics) at an early
undergraduate level.

Start with the Lagrangian and Hamiltonian formations of classical mechanics
(Landau & Lifshitz - Mechanics). Then, study Quantum Mechanics (R Shankar -
Quantum Mechanics). Statistical Physics while not key here, will be useful for
building up an intuition (Landau & Lifshitz - Statistical Physics is good).
Classical Field Theory, i.e. Electromagnetism should now be learned (J.D.
Jackson).

Then, I'd recommend learning Calculus on Manifolds (Spivak) and Differential
Geometry (I can't remember a good textbook on this right now).

If you're at this point you will now have a solid understanding of the maths
needed to know GR and QFT. Zee has two good pedagogic books for these
"Einstein Gravity in a Nutshell" and "QFT in a Nutshell". Once you know QFT,
read a textbook on the standard model.

That'll get you most of the way there. Strictly speaking, you could do
possibly learn a lot less to understand this paper, but to be able to pick and
choose which parts of the above are actually needed would require a
significant amount of work in itself.

~~~
Balgair
For the uninitiated, Jackson's EM book is considered _the_ book on E&M. There
really is no other book to learn from, if you want to learn EM correctly.

It is also horrifically difficult even for dedicated PhD students at top 50
physics programs.

Story time:

As an undergrad I had a TA that was in the astrophysics program. He told us a
story of a final he had to take in his EM class, using Jackson, of course. The
final was to present his solution, if any, to the PI. Pass or Fail. He went
home and started work on the problem about three weeks before the due date.
When his wife would go to work, he would be sitting at the kitchen table, when
his wife came home, he was still at the table. For weeks straight. As the
deadline got closer, he started sleeping less and working on the problem more.
In the last few days, he stopped sleeping entirely. Eventually, he gave up on
the problem and took the bus to campus to report on his failure and receive
the Fail. Once his deprived mind relaxed on the bus, he had a Eureka moment
and was able to solve the problem. Unfortunately, his sleep deprivation caused
him to hallucinate. While presenting his hastily put together findings, he was
trying to dodge imaginary bats, deal with imaginary blaring car horns, keep
from falling asleep while standing, and present very nuanced and complex EM
equations. After the presentation the PI said: "Pretty Okay", and passed him.

This is considered a _slightly_ atypical end to a semester with Jackson.

~~~
messe
How bad Jackson is depends highly on which problems are attempted and in which
context. The content is fine and perfectly understandable. We used it during
my third year of undergrad. Homework mostly consisted of the easy-to-medium
problems, and self-study could focus on the medium-hard.

Between that and the highly-abstract statistical physics course (it started
with an introduction to differential forms), I learned more in my third year
of college than in any other.

That said, I now work in IT.

------
m3kw9
Counter productive way to travel as it takes longer to use this worm hole to
get to point B using conventional travel. But it seems like a good way to
travel to the future. Just skip to point 4 in the doc.

------
klyrs
It sounds like things falling into wormholes accelerate terribly -- a natural
particle collider? Should we be able to see the detritus?

------
edna314
Bro, what's negative energy?

------
aaron695
I thought this was simple. You can't go faster than light.

If you go through a wormhole (Or just send information) you go faster than
light (Ignoring Hollywood's incorrect movie Event Horizon where you just bend
paper), so you go back in time.

So it's not possible.

Because you can kill you father (or something mathematical with information)
which is a paradox.

End of story.

~~~
yellowapple
I don't understand why "faster than light" automatically implies "go back in
time". If it takes me 10 seconds to travel 10 lightyears, then that means I
should still be traveling _forward_ in time (specifically by 10 seconds), no?

Like, it might apply on a "moving through local space faster than light" sense
because physics is weird like that, but the whole idea behind wormholes is to
shrink the actual distance traveled (from the traveler's point of view).

~~~
ikeboy
Because of relativity, you can have locations A and B in spacetime and a frame
of reference such that A happens before B and a different frame such that B
happens before A.

So, if you're at A, you can travel faster than the speed of light and arrive
before B happens. Then, after B happens, you can travel back to before A
happens.

~~~
komali2
Wait whaaaat? This is the first I've heard of this. I've a vague understanding
of causality. I thought the arrow of Time moved in one direction only? How can
A come before B come before A from, from one observer?

~~~
avmich
Novikov explains it approximately this way.

Suppose you have a wormhole between points A and B. So from A to B - and from
B to A - you can go by two different roads, one is pretty long (say, 1 light
month), and another is very short (negligible distance).

Next, suppose B end swiftly rotates around point A, so fast that time in B
goes slower than time in A. This means clock in B is going slower than in A,
and over 20 years in A only 10 years will pass by clock in B. That can be
confirmed by observation - telescopes in A will see slower clock in B,
telescopes in B will see faster clock in A (it's B going around A, not vice
versa).

That is, if we're talking about telescopes, looking through "regular" space.
Since A and B are also connected by the wormhole, looking through wormhole
will show us that clocks are synchronized. Over the wormhole, A and B are not
moving, so clocks don't deviate from one another.

We can stop B flying around A now. Now suppose B clock has accumulated 10
years of difference from A clock - again, looking via "regular" space. We're
leaving point A, flying to point B over the "regular" space and spending 5
years - way slower than speed of light, so our clock is practically
synchronous to A clock. At the start of flight, A clock show 20 years, and B
clock is 10 years, and by the end of flight A clock is 25 years and B clock is
15 years. After arriving at B, we jump into wormhole and get back to A, when A
clock shows the same as B clock - that is, 15 years. According to A clock, we
left at 20 years and came back at 15 years. Time travel.

~~~
Acinyx
Nice explanation, this made more sense to me than most of the explanations I
have heard about this before. But, wouldn't this just constrain the possible
features of a wormhole? The issue is fixed if traveling/observing through the
wormhole has the same time dilation:

Both through telescope as through the wormhole, the clocks can be observed to
go slower. After 20 years at A, both the telescope as observation through the
wormhole show 10 years have passed at B.

If we don't stop B from spinning: The regular space traveler takes 5 years, as
observed from A, to reach B, so reaches B at A:25 years, B:12,5 years. If they
leave immediately after arrival, they'll end up again at A at A:30y, B:15y.
Otoh, the wormhole travel leaves at A:20y ends up at B at 10y and gets back to
A immediately: A still at 20y and B at 10y. Mixed travel:regular travel starts
at A:20, B:10y, reaches B at A:25y, B:12,5 and jumps back through the wormhole
at the same time as seen from A and B.

~~~
Ixio
Exactly ! Why don't we suppose traveling/observing through the wormhole has
the same time dilation ?

I've heard of FTL=time-travel a couple of years ago for the first time and I
would love to be able to argue with someone knowledgeable about it to
understand. I hoped this HN thread would have answers. However all the answers
here seem to have holes in same.

I'm starting to wonder if FTL=time-travel isn't like Schrödinger's cat: a
hypothetical thought experiment terribly misunderstood by the masses.

~~~
ikeboy
If travel through the wormhole takes exactly as long as travel via space, what
kind of wormhole is it?

