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Travel through wormholes is possible, but slow (phys.org)
230 points by lelf 8 days ago | hide | past | web | 179 comments | favorite

I'm not sure if this is the researchers' issue or is an issue with the scientific press, but it would help if the "discoveries" theorists made with their hitherto unestablished and untested theories like various string and QG based theories were not touted as discoveries about the real world.

"Discoveries" about the mathematical structure of these theories are actually incredibly important even if no current day experiment can conceivably test them. Special and general relativity were discoveries made in this way (at least to an extent), and now general relativity is important for the proper functioning of technology as "trivial and boring" as GPS. Even earlier in our history, much of thermodynamics was developed in a similar fashion.

See the sibling comment for another version of this argument, but finding the weird mathematical coincidences between the competing mathematical theories of nature is very useful. In other words, there are mathematical and logical tests that can be as important as experimental tests for the progress of our understanding of nature.

Came here to (wrongly) correct your statement, as I remembered that the only relevant effect was from special relativity.

It turns out it is the exact opposite: general relativity effects prevail [0]. Thanks for forcing me to check!

> Special Relativity predicts that the on-board atomic clocks [...] should fall behind clocks on the ground by about 7 microseconds per day [...] due to the time dilatation effect of their relative motion.

> Further, the satellites are in orbits [...] where the curvature of spacetime due to the Earth's mass is less than it is at the Earth's surface. A prediction of General Relativity is that clocks closer to a massive object will seem to tick more slowly [...]. A calculation using General Relativity predicts that the clocks in each GPS satellite should get ahead of ground-based clocks by 45 microseconds per day.

> The combination of these two relativitic effects means that the clocks on-board each satellite should tick faster than identical clocks on the ground by about 38 microseconds per day (45-7=38)!

[0] http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps....

They're incredibly important, but they shouldn't be touted as facts until there's some consensus that they are facts

I think the key here is the word "fact". Scientific models are models. They are good models if they correspond with measurements that we make in the real world. The are even better models if they make a prediction that we can test in the real world. However, a model is never a "fact". "The FSM did it" is always going to be a possibility, even if it is an incredibly remote one.

We use scientific models because they are useful not because they are fact. Even if our model does not always match our observations it can still be a useful model in some circumstances. It's very important when talking about science that we understand that it isn't fact. It is a model. It might be a good model. It might be a bad model. It might be a useful model for our application. It might be a poor model for our application. That's it.

When you see a headline that says "X is Y" and it's about a scientific model, what that means is "If our model is consistent with the real world then the model predicts that we should find that X appears to be Y in the real world". But that's a bit too long to put in a headline and you would have to do it for every scientific conversation.

It is extremely unfortunate that on the first day of junior high school when you start doing "proper" science classes that they don't sit people down and explain what a scientific model is. Mostly I think it's because the teachers don't know, because their teachers never taught them.

Mathematical theorems (especially no-go theorems, one of the most powerful tools in physics) are at least as much of a fact as an experimental measurement. I can concede that a pop-sci outlet should be clear about what is an experiment and what is a mathematical theorem, but was it really not clear in this case?

This is a sincere question, and I care to hear your opinion: do you believe that a reader of phys.org would need more than a glance at the article to know this is a discovery about the mathematics of general relativity, not an engineering breakthrough in the creation of a scifi-like hyperdrive?

> Mathematical theorems (especially no-go theorems, one of the most powerful tools in physics) are at least as much of a fact as an experimental measurement

That's an overstatement. Measurements are more important than theory. We cannot form theories without measurements, and yes theories inform our measurements, but science always begins and moves forward with measurements.

General relativity, quantum computing, some parts of thermodynamics/information theory/statistical physics, some parts of quantum field theory, some parts of condensed matter physics are all things that started as purely mathematical statements. I am not trying to diminish the monumental importance of empirical measurements, but please do not diminish the importance of logical consistency and mathematical constraints. We can say a lot about our universe with great certainty even though in same cases making direct measurements is orders of magnitude beyond our technology.

Really? Facts are now subject to consensus agreement?

Double-plus goodthink, comrade!

QG is funny.

There are some results around QG, such as holography, which seem to be universal. That is, they make sense with strings, loop quantum gravity or any of about ten other lines of work that people can do quantum gravity calculations with today.

If you can prove that all of those have to say the same thing, that is a powerful result and probably means something about our world.

It seems pretty reasonable that wormholes could exist so long as they don't form closed-timelike curves, so I think these people are getting at the quantum roots of the "cosmic censorship principle".

> It seems pretty reasonable that wormholes could exist so long as they don't form closed-timelike curves

"Wormholes" are two entangled black holes that have been subsequently moved light years apart, preserving the entanglement during the move. They are a great mathematical toy for exploring the nature of entanglement.

But that's it. We have trouble preserving the entanglement of just a few ultra cold particles for a few milliseconds. I am far^^^far more likely to fall onto the floor by quantum tunnelling through my chair than a useful wormhole ever appearing. Postulating they actually exist is not in the slightest bit reasonable.

I think it goes beyond the scientific press. There seems to be a general tendency to squash the intricacies of anything and react impulsively to some red herring or whatever; such comments dominate all online forums I've ever seen.

Here is a fantastically interesting article that maybe has some new insight on the nature of spacetime; top comment on HN thread about it is some person loudly and incredibly pretentiously mistaking their own misunderstanding of the intricacies of 'truth' in science (and how there are different levels) for some flaw in the work itself.

You know, the underlying sentiment here is a good one. How do we know what we know, what do our theories really tell us, etc. All excellent questions. But you didn't express that at all, instead you say these things shouldn't be 'touted as discoveries about the real world.'

That's all you man! No theorist ever has wanted people to think this of their work, it slaughters the beautiful intricacies of it and leads to public relations disasters like this.

Don't go misunderstanding shit and then confidently be blaming it on other people man. Rhetoric matters.

The whole "it's just a theory" thing has done so much harm to public understanding and appreciation. It's an impossible starting point for a conversation, if you think "it's just a theory", you're not wrong, as much as entirely missing the point. How do you start with that and get to an understanding that things aren't always absolutely right or wrong, that contexts and assumptions matter, that things can be true in one setting (the math) and uncertain in another (the real world). That for most things what we are more than anything is uncertain. That there are many different kinds of uncertainty.

How are the subtle intricacies of things (that the answer to almost everything starts with "well, that depends...") supposed to survive forums where conversations are heavily selected for ability to grab attention? Not a rhetorical question, if you got ideas I want to hear them.

PS noobermin, I don't mean to be overly-critical of you although it sure sounds like it. I'm using 'you the pronoun'. Just something I think about a lot that you catalyzed me into trying to express...

IMO, your premise is a strawman. I don't detect any "it's just a theory" sentiment in the top level comment. What the comment says is that mathematical statements about "hitherto unestablished and untested theories" should not be taken as statements about the world.

This, to me, shows a rather sophisticated understanding of scientific truth, namely that we should demand that a scientific theory (as opposed to a mathematical construction) should be falsifiable. AFAIK, there is no question that the mathematics of string theory et. al is sound; the question is whether these theories are physical, and whether they are falsifiable. These are the exact objections the top-level comment makes when referring to "unestablished and untested theories".

There is an important point you are not addressing: it is one thing to make a statement about one single mathematical construct (it is cute, but not a big deal). It is another thing to make a statement that constrains a whole family of seemingly disconnected mathematical constructs (this is now a serious constrain on what the laws of the universe can plausibly be).

From a sibling comment:

> There are some results around QG, such as holography, which seem to be universal. That is, they make sense with strings, loop quantum gravity or any of about ten other lines of work that people can do quantum gravity calculations with today.

> If you can prove that all of those have to say the same thing, that is a powerful result and probably means something about our world.

I'm not exactly sure which version of "If you can prove that all of those have to say the same thing...." you're arguing for. It doesn't scientifically matter what statements you can make about any number of mathematical constructs if none of those constructs make testable predictions. Remember, falsifiability is a necessary condition for a construct to be a valid scientific theory.

OTOH, it does matter if you are able to make a statement of the form "Any mathematical construct that accurately describes X must have property Y." It is not clear that quantum gravity (or the linked article) meets this latter standard.

Ah, I think we have a deep "philosophy of science" disagreement. Basically, it is not just "falsifiability", but also "probability" of being correct. Probability that can be informed by things like formal versions of Occam's razor (e.g. Kolmogorov complexity, Akaike information criterion, etc).

Here are a few premises on which I based my statement (I will pick one particular venue of scientific research, so I will not speak in all generality. You can of course disagree and say that it does not generalize at all, but I think this would be a philosophical discussion, i.e. it does not matter at all that we have different opinions, as both are equally valid ways of pursuing scientific truth):

1. Computational complexity is a science on its own. Computational complexity also makes useful statements about the limits of the physical laws in our universe (a la "extended Church-Turing thesis" or Aaronsons "NP-complete problems and physical reality").

2. NP=P vs NP!=P is a question that has a definite answer within the relm of science but we do not know the answer yet. The answer will constrain what the permitted laws of physics are due to point 1 above.

3. There are a lot of clues that NP!=P coming from very separate disjoint fields of math. Mainly because we already know there are a lot of "phase transition"-like phenomena when we apply approximate algorithms to problems that can be parameterized to be NP-complete only if some ε is larger than some critical value.

4. These "phase transitions" are purely mathematical constructs, but due to the previous points they constrain what is permitted in the universe as strongly as any 5-sigma measurement in a particle accelerator.

To bring this back to the discussion of speculative theories of quantum gravity: if all of the competing theories of quantum gravity (all of them being very speculative and unproven) have a handful universally agreed on predictions (although derived in completely separate ways), this is as strong of a constraint as any 5-sigma measurement in a particle accelerator or cosmological observation.

Or if you permit me to attempt to phrase is it in yet another way: there are a ton of theory assumption behind any 5-sigma (or 10-sigma) experimental measurement. These assumptions are the same ones that inform the purely mathematical constraints. If both the math constraints and the interpretation of an experiment are based on the same assumption, why are you taking the interpretation of the experiment any more seriously than the pure math.

Sorry for the length of this text - I am finishing my dissertation this week (doctorate in physics), so this is very much on my mind at the moment.

I really appreciate the clarity of this comment. While hacker news is certainly one of the better forums, the amount of armchair analysis and pseudointelectualism, especially on scientific non-IT posts, is pretty frustrating. It reminds of the "middlebrow dismissal" style https://news.ycombinator.com/item?id=5072224

I think for anyone for whom this theory is at all relevant, it's already clear that this is a theory, not a proven fact.

The fact that its theoretical is mentioned in the article for anyone that bothered to read past the first few paragraphs. For the rest of us, it just makes for interesting party conversation whether the theory pans out or not (which couldn't be proven by actually transiting a wormhole within any of our lifetimes)

So no harm, no foul -- anything that makes theoretical science interesting in the popular press is a win in my book.

Can someone point out where the article says why it's slower? I'm having difficulty unpacking:

"The new theory was inspired when Jafferis began thinking about two black holes that were entangled on a quantum level, as formulated in the ER=EPR correspondence by Juan Maldacena from the Institute for Advanced Study and Lenny Susskind from Stanford. Although this means the direct connection between the black holes is shorter than the wormhole connection—and therefore the wormhole travel is not a shortcut—the theory gives new insights into quantum mechanics."

Why is the wormhole not a shortcut?

Based on the colloquia I watched by Lenny Susskind, the problem is that you can put something into a wormhole, but to get it out the other end, you have to carry the encoding you get to the other end of the wormhole to decode the output. Because the distance to the singularity grows at the speed of light, the length of the wormhole is essentially infinite. It is only the operator you get from putting the object into the wormhole that lets it tunnel through that infinity, so no shortcut.

EDIT: Here is the lecture I'm referring to: https://www.youtube.com/watch?v=nEDFh8ma9zM

> the problem is that you can put something into a wormhole, but to get it out the other end, you have to carry the encoding you get to the other end of the wormhole to decode the output.

That sounds a lot like how entangled particles can't be used to communicate faster than light.

While you can make observations immediately, you can't turn them into useful information about the other end, at least not until you get missing data which has to reach you by normal means.

Hence the focus on using entangled particles as a kind of tamper-detector or "reusable random one-time pad", rather than for transmitting information.

That is precisely the lesson of the ER=EPR principle, which states that every entangled pair really has a 1-qubit wormhole connecting it, and the space inside a macro-scale wormhole is the consequence of combining all those tiny wormholes together. Wormholes are entanglement.


Two entangled wormhole apertures function as Star Trek style transporter pads. Feed mass into one hole, scanning it as it goes in. Transmit the pattern to another aperture of the hole, using electromagnetic energy at the speed of light, and when that end ejects a mass, apply the pattern to it, so it resolves into an exact copy of what you put in.

The distance the mass travels may be shorter than the distance the energy travels, but it can't resolve exiting mass as that object until the information--that had to travel at the speed of light--arrives.

So you could potentially use a wormhole as a suicide machine that transports a copy of you, that thinks it actually is you, to a distant location no faster than the speed of light, in zero subjective time for the thing that will then think it's you.

Is that a reasonable interpretation?

I don’t think the suicide booth model of a teleporter fits a quantum teleporter model, only the 3D printer teleporter model. From a quantum point of view, all (e.g.) electrons are indistinguishable excitations in the same field, and it’s the pattern that makes you “you”. If you’ll forgive a bit of poetic licence, quantum teleportation seems more like Discworld magic, where you have to exchange two identical sized lumps of matter.


Edit:Lol, someone else also had this link as a reply to a similar thought.

This sounds like the science-fiction version of a cryogenic scam.

So we've uncovered the universes version of cyptography?

It's more just the encryption method without decryption.

Native cryptography, I'd say

> Because the distance to the singularity grows at the speed of light,

doesn't our universe expand at the same speed?

As the sibling poster implies, not only are there black hole horizons, but we are ourselves inside of a cosmological horizon. Objects outside the horizon are impossible to see, and objects approaching it from the inside will redshift and disappear from view the same way they do when entering a black hole from the outside.

This is a false horizon. See https://en.wikipedia.org/wiki/Ant_on_a_rubber_rope.

At least theoretically we should be able to receive signals from arbitrarily far away no matter the expansion of the universe. They'll be redshifted like hell though, as you say.

Things are moving away from us at a speed proportional to their distance. The fastest objects are actually faster than the speed of light.

I thought nothing could move faster than light?

Special Relativity states that no two objects may pass each other faster than the speed of light. Space itself isn't bound by this restriction. To wit: no thing can move faster than the speed of light, but space is not a thing.

Space is dynamical. It can stretch and expand and even break, but it doesn't move. The result of this is a cosmological horizon that prevents these objects from communicating, because the distance between them is growing faster than light can cross it. This is the same reason you can't escape a black hole.

Nothing's moving. It's like if you ran a 100m but while you were running, they decided to make it a 200m.

If you speed up, you can finish the race in the same amount of time. Light always finishes the race in the same amount of time from each observer's perspective. It can always speed up because it's massless, but you have mass and there is a limit to how much you can speed up. According to general relativity, an observer outside of the racetrack won't see light change speed, nor will you. But both of you will perceive distortions of space and time to accommodate light's "change in speed" to make it look as if nothing's changed.

Back to the cosmological horizon... We don't see a big jump in the racetrack because the distance between 100m and 200m isn't too massive; likewise, gravity and other forces hold objects together even though space is expanding and pulling them apart.

But there is a certain distance where gravity and other forces can't keep things together. Where that 1000k becomes a 10000k. The pull from one galactic cluster to another is just too weak. Anything past this point is moving away from us. That's why only galaxies close to us aren't redshifting away. But any observer anywhere in the universe would observe that they are at the epicenter of an expansion where everything is moving away from them.

:D is the universe expanding, or revealing more of itself? if the universe is expanding at the speed of light, doesn't that imply that just light is reaching us more from further away places? sorry to be off topic but that comment gave me this brainfart.

The universe is revealing more of itself as light reaches us from farther away, but because the universe is both expanding and that expansion is accelerating, there is a maximum distance we will ever be able to see: the Hubble Distance. I don't think the universe is old enough for light to reach us from that far yet, which is why we can still see the cosmic microwave radiation, but give it a few trillion years, and we won't even be able to see other galaxies because they will recede from us, redshift, and disappear.

No, there's actually more space constantly being added to the fabric of spacetime. So if you take 1 cubic meter of space, eventually it will become 1.01 cubic meters, then 1.02, etc. This isn't noticeable at distances within the galaxy, but it is very noticeable when observing distant galaxies.


The Average Null Energy Condition (ANEC) makes it so there can not be a traversable wormhole joining two otherwise disconnected regions of spacetime. So by construction, any infinite null geodesic (a light ray) which makes it through the wormhole must be chronal (causally connected). This means there can be no traveling faster than light over long distances by going through one.

So that's it, then? Some thing, say, a million light years away from another thing is in practice entirely inaccessible to civilizations existing on that other thing, requiring a minimum of a million years to reach?

This depends on what do you mean by 'inaccessible'.

Going there and back again, and telling your pals how things are 1000LY away is likely impossible.

Expanding your civilization to more and more habitable celestial bodies, slowly but relatively surely, is entirely possible. This is how e.g. plants colonize vast spaces, being limited by the speed of their growth often by inches per lifetime. (You should also consider the amount of resources the plats dedicate to it, and their success rate.)

Extending human lifespan (perhaps using methods of hibernation, perhaps not) is easier technologically than basically any viable form of crewed interstellar travel.

I get what you are saying, but it seems like the plant approach is mostly useless to humans. If the people on opposite sides of a galactic civilization are so far away that they cannot meaningfully interact, then it seems like that's no different than the other person not existing from their perspective.

Depends on the definition of useless or meaningful. If meaningfulness only extends to immediate political, social, economic or technological interactions then maybe an organic colonisation seems useless, I guess.

Unlike plants, through the power of electromagnetic communications and a culture based on shared knowledge, humans will know the others exist, even though that interaction will be slow with likely little-to-no-influence on their local evolution.

There would be huge cultural meaning even despite the lack of immediacy. Imagine living in a world where you know that there are other humans like you in space, living on other worlds light-years away. You might not be able to communicate immediately, but you know that they are there, and the universe is not so empty to you. You could look to the night sky and reminisce on your great(*n) grandpronoun whose progeny have built a thriving colony among the stars. Entire institutes would exist dedicated to collating and outlining the historical expansion of mankind among the stars, even if that knowledge takes centuries or millennia to accrue.

Also we can not say those other humans may as well not exist, because there is no telling what each new colony will go on to achieve. Their cultural, scientific and philosophical development independent of the influence of Earth's history and challenged by new environments could yield new perspectives, ways of thinking and practical inventions whose value far outweighs the large delay in communications.

If we're talking galactic scale, then the creatures who ultimately wind up on the other side of the Milky Way two hundred thousand years from now would likely bear only a passing resemblance to the humans who expanded from Earth. However barring a catastrophic event that erases their knowledge of their history, they would owe their existence in their history books to this tiny planet.

Finally, the fear that we are the only planet with human life would be vanquished, so even if we all died from pollution or meteorite, we'd know that somewhere the legacy of our species (and selected companion lifeforms) would continue, which I don't think is useless or meaningless either.

> I get what you are saying, but it seems like the plant approach is mostly useless to humans

Yes, and as humans are to plants, so our space faring descendents will be to us.

But aren't there massive gaps where an intermediate celestial body to perform this jump on will be simply too far away for traditional space travel?

Probably not. On the timescales of millions of years, the only thing that really matter is whether it's physically possible, and it looks physically possible to colonize other galaxies.


I'd be pretty surprised if the jump between galactic groups is much worse.

On the bright side, due to time dilation, you can still make the trip in your lifetime.

You don't get much time dilation until you start hitting speeds mostly exclusive to accelerated subatomic or nuclear particles. It's nearly zero until you get past 0.5 c.


If by the bright side you mean you would only make it there it there as pure energy. Mass is converted to energy as it approaches C (Light Speed). Though getting mass to actual light speed would require infinite energy, so that point is moot.

Let's say you get to 96% C. You would experience 28% of the journey. Taking into account the the time to speed up and slow down from C, you're looking at over 290k years from the perspective of the passengers.

At 99% C, you would experience over 14% of the journey (About 142k years).

Mass is converted to energy as it approaches C (Light Speed).

Not so much.


Try this thought experiment. Let's say you had a magic Bussard Ramjet rocket which scoops up energy and reaction mass from space and can accelerate forever. There are no special reference frames. So what happens if the rocket accelerates then shuts off its engine at the point where the "relativistic mass," as measured by an un-accelerated observer, should make the rocket disappear behind an event horizon?

From the POV of people on the rocket, they accelerated, then stopped accelerating. From the observer's POV, the rocket turned into a black hole? One reference frame now seems "privileged" or different somehow. How do we square this with relativity? Also, what happens if the rocket turns around, then decelerates? Wouldn't that constitute them returning from inside of an event horizon?

The answer, is that "relativistic mass" is actually just a pedagogical fiction.

(EDIT: Also, a lot of the redonkulousness in the thought experiment sneakily comes from rockets that can magically accelerate without worrying about where the fuel and energy come from. If you worked out how much fuel and reaction mass would be needed by a real rocket to perform such a feat, you'd get "unphysical" amounts of matter.)

> Mass is converted to energy as it approaches C (Light Speed).

Uh, I think it's the other way around: the energy you pump in becomes additional mass.

Well, theoretically they could load their civilization up on a giant ship and move their civilization there over the course of a million years. Likelihood of success? Probably not great, but possible.

Everyone is missing the obvious solution. If we're talking about tech this fantastical, the best idea is to ditch our ephemeral biological bodies, jump onto a synthetic medium, and call it a day.

Hit pause so the journey takes a fraction of a second, or spend 1000Y in a VR - do whatever you want. I don't see a future where we're this advanced yet still content with our frighteningly fragile bodies.

Perhaps it's because building a giant ship that can carry countless generations of inhabitants many light years is really more of just an engineering problem. All the challenges (of which there are plenty) all have reasonably known solutions. There's not really all that much novel technology required. Just better tech than we have, and a lot of it, to be sure.

Uploading a consciousness into a computer and have it remain "you"? That's completely foreign to what we know today. I'm not saying it's categorically impossible; to your point, if a civilization has advanced to the point where the above is ship is feasible, surely they must have picked this up along the way? Maybe, but maybe not. We don't even know if it is possible. But keep a shitload of people alive in space for a long time? Sounds plausible, even if it is enormously difficult.

The future you don’t see describes the present. We are (at very great, politically untenable cost, to be sure) capable of sending a ship full of humans and supplies elsewhere at a reasonable fraction of c. Our ability to do this continues to grow; although due to resource scarcity it’s not clear if efficiency gains will ever make it cheaper to do in the future than now.

We don’t even know where to start replacing our bodies. AI? Genetics? Cybernetics?

I mean at that point you don't have to choose - you do all those things, plus have some more of you spend a bunch of time figuring out the philosophical ramifications of bringing it all back together.

Add some check processes which periodically restore an old backup and have a conversation to see if the backup agrees to a merge as the moral monitoring system.

Or better yet, do the "Contact" thing, and just transmit information. Start with something to generate interest. Then maybe some (hopefully appreciated) knowledge and/or technology. Then instructions for building VR or robots, and data to load them with.

>So that's it, then? Some thing, say, a million light years away from another thing is in practice entirely inaccessible to civilizations existing on that other thing, requiring a minimum of a million years to reach?

"We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far." -- H.P. Lovecraft, 'Call of Cthulhu'

We're just a random species of ape too smart for its own good, only here to ponder the universe at all because an asteroid happened to wipe out the dinosaurs 65 million years ago. The universe doesn't owe us anything.

At least we have telescopes and science fiction, though. The dinosaurs didn't have either.

You're correct, at least according to Kurzgesagt


According to physics as we currently understand it, yes.

As always, soon we will discover another way, or there will be a different theory that will allow bending the rules.

Not always. Faster than light travel has never been bent.

Well, we are able to research FTL for only a few decades. Give it a few more due to complexity. Few ages ago people thought that the world is flat...

Also, there are theories of FTL: https://en.wikipedia.org/wiki/Faster-than-light

Shadows can move faster than light.

I'm kind of relieved by this.

The last wormhole conversation I had with someone, I imagined a weapon using a short-distance wormhole with the ends opposed 180 degrees, and using a star's own gravity to tear chunks out of it. Everybody dies from massive solar flares.

Of course time travel books, wormhole researchers, and myself all make the same mistake over and over: If you made a wormhole or traveled in time, why do we assume that the frame of reference of the system is our star? Sol is whirling around our galaxy and an alarming rate, and that's moving through the universe at a huge velocity. Why would the hole you're trying to make in space move along with our solar system?

If I traveled back to five minutes ago I'd die in hard vacuum. I'd have just enough time to realize how stupid I am. Similarly, every time I try to use the same wormhole it would be farther from where I am and the other end farther from where I want to be.

AIUI wormhole mouths don't have a direction. They're spherical.

The picture of a wormhole as a bell-shaped indentation in a sheet, like the graphic on this article, is an artifact of trying to explain 4-d concepts in 3-d shapes (in 2-d images). For a being in the 2-d sheet, the wormhole is a circularly symmetric spot of weird-shaped space. In real 3-d space, a wormhole is a spherically symmetric spot of weird-shaped space.

True. You could still use this to make two Lagrange points near the surface, mucking up everything. The fact that the hole has to be longer than the distance traveled would greatly reduce the gravitational field coming out of the hole.

You could still drop one end of the hole into the sun... (and I’ve just realized this was a Farscape plot and therefore how the idea got into my head in the first place)

Presumably, if you're smart enough to make a time machine, you'd be smart enough to calculate the target position in both time _and_ space.

I suspect if you had that much understanding of orbital mechanics, you'd be a billionaire already and not worry so much about time travel.

No sensible protagonist or villain use time travel to become a billionaire. There are usually better pursuits involved.

Maybe this sounds a bit silly, but this is honestly one of the most mind-blowing thoughts I've read on Hacker News. Thanks, I can't believe I never thought of this myself in the past. :)

You don’t really explain how the assumption leads to the conclusion — and I’m left with the impression you used many words to say “they just assumed you can’t”.

Could you elaborate?


Looking into energy conditions further, they are literally assumed restrictions on the equations because physicists felt some predictions were unphysical.

I’d really like if someone could explain if there’s any justification to what I was responding to beyond “well, because we assumed it should work that way”.

I think it behooves the physics community to be honest which claims are conclusions and which are their assumptions, and the specific reasoning that leads from assumption to conclusion.

I definitely get your point. One difference between theoretical physics and just math is we have since we use math as just a tool to describe the world, we still have to input physical assumptions to make any sense of what we see. There are many instances of things being mathematically "OK" but we don't think physically exist. See "White Hole" for instance.

I will try to give a better explanation later today! Funny enough, I am off for the section for the QFT2 that Daniel teaches right now, hah. I can also ask him personally questions later in the week.

Who is the "we" who thinks White Holes don't exist?


Black holes are hard to notice, except by side effects, but we know great many of them, end even portrayed one.

White holes would be relatively hard to miss, because they must be shining very brightly. One of the current theories suggests that the big bang (or "a big bang") was a white hole: every black hole is a white hole producing a big bang a parallel universe. We've already had ours, and are lucky enough to still register its echo as the CMB.

Without negative matter, it's impossible to build a wormhole that's shorter than the distance through normal space.

This piece of math shows that it may still be possible to build a wormhole which isn't shorter than that distance. Obviously that wouldn't be much of a shortcut, but the potential research and (maybe) real-world applications are still impressive.

That’s not what I was asking.

I was asking about the particular usage of the average null energy condition as justification to rule out wormholes: why isn’t that just begging the question by assuming your conclusion? and how does that particular assumption actually lead to the conclusion there can’t be wormholes?

It’s interesting the downvotes for asking someone to support a scientific claim, and be clear where they’re making assumptions versus reaching empirical conclusions.

That's right. When you have a mathematical theory, there are often extremal cases that predict strange things that have never been observed. At this point you have a choice to make:

1) Assume the mathematical theory is too permissive, and rule out the things you have no reason to exist, and hope to find a more elegant theory (on the controversial metaphysical assumption that simpler/elegant theories are more likely to be correct)

2) Assume that the mathematical theory is pointing you in a direction to search for a new phenomenon, and build things like superconducting supercolliders to search for empirical evidence.

With wormholes, we're a bit stuck in that we are decades to centuries away from empirically testing the theories, so physically the Average Null Energy Condition is moot -- it's fine math to do, as groundwork/scaffolding for future physics, but it doesn't say anything physically until we get empirical evidence for or against it.

If that condition didn’t hold, we would expect to see a lot of phenomena that we don’t see, which makes it a poor model for reality.

>To date, a major stumbling block in formulating traversable wormholes has been the need for negative energy, which seemed to be inconsistent with quantum gravity. However, Jafferis has overcome this using quantum field theory tools, calculating quantum effects similar to the Casimir effect.

Prof. Stephen Hawking has explained the Casimir effect in hist last book 'Brief Answers to the Big Questions' in the chapter talking about Time Travel with Wormholes.

"Imaging that you have two parallel metal plates a short distance apart. The plates act like mirrors for the virtual particles and anti-particles. This means that the region between the plates is a bit like an organ pipe and will only admit light waves of certain resonant frequencies. The result is that there are a slightly different number of vacuum fluctuations or virtual particles between the plates than there are outside them, where vacuum fluctuations can have any wavelength. The difference in number of virtual particles between the plates compared with outside the plates means that they don't exert much pressure on one side of the plates when compared with the other. There is thus a slight force pushing the pates together. This force has been measured experimentally. So, virtual particles actually exist and produce real effects.

Because there are fewer virtual particles or vacuum fluctuations between plates, they have a lower energy density than in the region outside. But the energy density of empty space far away from the plates must be zero. Otherwise it would warp space-time and the universe wouldn't be nearly flat. So the energy density in the region between the plates must be negative"

When ever I think of traveling through a wormhole/blackhole, I imagine you would be squished and crushed and come out the other end as pure vaporized energy.

This makes me wonder, if there is the potential for our beings (or things) be able to be vaporized and then recreated to original form.

If we are just mass and particles, this should be possible?

If you could 3d print things at the atomic level, then you could instantly advance the human race to a post scarcity society. It's the holy grail of 3d printing and of course everyone wants to do it.

Your question has philosophical implications beyond just the mechanics, however.

>If you could 3d print things at the atomic level, then you could instantly advance the human race to a post scarcity society.

You still need energy, and you still need something to print with (not just the printer, but whatever substrate provides the atoms,) and the process is going to be somewhat inefficient due to thermodynamics. 3D printing a vegetable, likely, would still consume more resources than simply growing one in a garden. Plenty of room there for scarcity.

Uncertainty principle says...probably not. It's impossible to make a complete copy of the pattern.

Even aside from that -- it's unlikely to be practical to scan something down to the smallest level level of matter, because the tools we use to manipulate things can't manipulate things smaller than their own finest details. So there's a "glass wall" in that you can only replicate things less finely detailed than the replicator. That works fine for macroscopic things (that's why you can buy a 3D printer today), but is implausible for things that we believe to be as finely detailed as our machines.

> Uncertainty principle says...probably not. It's impossible to make a complete copy of the pattern.

That depends on what "the pattern" is. You can make an "exact" copy of a digital file, but that's because the semantics of digital data don't depend on the fine details of the physical representation (that's the whole point of going digital). We don't yet know what level of detail of our physical state actually matters. If you take a single atom in your brain and move it somewhere else, does that matter? Probably not. What about ten atoms? Again, probably not. But at some point as the number goes up the answer must change. We don't know where the boundary is, and we don't know how close it is to the theoretical and technological limits of copying. But I don't think we can rule out the possibility of cloning a human brain in principle based on current knowledge.

That's what the "Heisinberg compensators" in star trek fix. I heard this phrase in an episode once, and decided to figure out how that could even work...

What I came up with was the idea that the scanning stage doesn't need to gather exact data because it really doesn't matter. You just need to get averages, and then build up a model that matches the statistics... (you don't need to discover the exact energy and momentum of every particle, just measure the temperature)

Basically you get teleporter jpeg compression... good enough to fool you, just don't use it too many times without keeping the raw data:)

"Heisinberg compensators" it's a clever lie that La Forge uses to fool Moriarty on a chapter.

They are mentioned several times, but no description is given for how they might work.


The philosophical implications of this are the subject of one of my favorite web-comics: The Machine, from Existential Comics http://existentialcomics.com/comic/1

What these two stories describe would surely be hell for a normal human and likely also equivalent AI consciousness.

On the other hand, if you could run even a simple computer program in such a context, it opens interesting possibilities. In "The Jaunt" they describe some of the periods lasting up to billions of years - imagine you could keep a simple algorithm (say prime factorization) running for that long, without the associated energy costs and get the results instantaneously from your point of view.

BTW, of course people from Orions Arm have put together something similar but actually remotely physically plausible using a concept called "Tipler Oracle": https://orionsarm.com/eg-article/48507a11adbd7

I don't think you can equate the teleportation station with sleep since sleep isnt a break in consciousness but more like a transition into a lower level of consciousness.

What about concussions?

Its all about information. The order of atoms to make a person is information. No information passes thru the event horizon of a black hole.

So, no.

> No information passes thru the event horizon of a black hole.

No information is lost. A copy of it can very well fall into the BH (and it does).

> No information passes thru the event horizon of a black hole.

that is only true in one direction though, right?

From the point of view of something falling in you are correct.

From the point of view of something further away watching the thing falling in, it takes forever. I think. Time dilation is easy to lose track of.

It's a neat demonstration of the holographic principle. From the point of view of an outside observer, there's no difference between the surface of the black hole and its volume; they're two different ways to describe the same thing, of varying usefulness. Reaching the 'surface' of the event horizon is equivalent to reaching the infinite future of the hole.

However, you'd still be spaghetti.

For a large enough black hole you could theoretically pass the event horizon pre-spaghettification since the radius between the singularity and the horizon would be large enough that the tidal force wouldn't be unbearable. You may have enough time to realize that you've now passed the ultimate barrier before you're eventually torn to shreds by the singularity.

> From the point of view of something further away watching the thing falling in, it takes forever. I think. Time dilation is easy to lose track of.

This has always made me wonder that if this is true: "From the point of view of something further away watching the thing falling in, it takes forever." Then how does a black hole increase in mass from the pov of "something further away," as things fall into it? Is it just the light coming from the captured object that gets stopped in time, and the mass does get absorbed increasing the black hole's mass in a more normal time frame?

that is my understanding as well.

it feels almost meme like that from an observer’s point of view, a black hole will have a bunch of stuff “stuck” on its horizon. i haven’t ever seen elaborations of how it would actually look though.

Ever play Katamari Damacy?

There is only one direction through the event horizon of a black hole.

I thought Hawking radiation was going the other direction, but that it doesn't carry information about the original mass/energy. Is that right?

I don't think there's a definitive answer there, nor any reason to believe Hawking radiation is produced inside an event horizon, rather than just outside it. The event horizon is pretty much defined by the boundary that radiation will not escape across, so I wouldn't assume Hawking radiation behaves any differently with respect to it.

That reminds me a bit of the Star Trek Voyager episode where the a group sends their dead from one dimension to another. Their bodies come through intact but some form of "neural energy emissions" is added to a local energy field.


You've just described a Stargate from the SG1 universe :)

Gates disintegrate objects that pass their event horizon, transmit the energy and "pattern" of the object to the exit gate which rebuilds them.

Essentially everyone in that universe that has stepped through a Stargate has "died" and it's their copies currently walking around.

Even if we are just mass and particles, then what happens if you just skip the vaporizing part. (https://www.youtube.com/watch?v=nQHBAdShgYI)

"To date, a major stumbling block in formulating traversable wormholes has been the need for negative energy, which seemed to be inconsistent with quantum gravity. "

it appears thus, most humans are inconsistent with quantum gravity :D:D

I would urge people interested in this topic to read the hard scifi work of Greg Egan. In particularly, Diaspora. It is fascinating how much overlap is between this mathematical work and his work of "mathematical fiction".

It seems to me that the speed of light, like conservation of energy, is just one of those fundamental “no free lunch” rules of physics that we just plain can’t cheat.

Why doesn’t this violate the topological censorship result?

It's possible.

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