Everything moves slower than [the speed of] light.
Unless you are in a scifiction story or a conspiracy theorist who believes in that sort of thing and stuff like perpetual motion machines.
The paper bending, sticking a pencil through explanation is science fiction.
That is faster than light travel and hence impossible.
Do less work, not faster work.
And that's why this technique is being described as a wormhole - it's a relatively good simulation of one in terms of some of the measurements they want to make and can be used to carry one of the properties we think a wormhole should be able to carry.
I mean, I send two light beams simultaneously, one directly to you, one off angle to a mirror which reflects and then reaches you too[0]. The direct one reached first because it had a shorter route, they both travel at c...we don't violate lorentz.
I think you're referring to a topology that would allow closed timelike loops which would imply grand father paradox issues? That doesn't violate lorentz which is local and doesn't care about global structure, but it leads to logical inconsistencies (which is global, I think...)? Enlighten me. Again, my expertise is not GR.
[0] If you want to be pedantic, we are both in the same lorentz frame...needs not to be said, but just in case :)
That's what I just said. Your objection is silly.
You're basically saying "Look, if light follows an extrinsically curved geodesic that goes into a black hole it takes 10 minutes to reach the singularity. But if we shoot it straight into the black hole, the math says it only takes 9 minutes. Impossible! That's science fiction! It's going faster than light!"
Information traveling through a wormhole is emphatically not going faster than light. It's just taking a shorter route to get to the other side. You can't necessarily violate causality like this; you can just bring objects closer together.
The mathematics on wormholes is quite solid and appears to admit traversable wormholes in principle. There are many reasons why it might not actually feasible to build or use one, but your objection isn't one of them.
If wormholes can exist you won't be able to send information through them.
I idea of information being sent faster than light is nuts. It might be mathematically interesting but that's it.
I really don't get the tolerance around this idea of faster than light travel which also means time travel.
> It might be mathematically interesting but that's it
That's exactly what they said about photons and antimatter. Both were discovered mathematically before they were discovered physically. "Oh, this is just a mathematical fluke, this couldn't exist in the real world."
The best physical theory we currently have admits the existence of wormholes. If you have a problem with that, then feel free to try to come up with an alternate physics that explains the world better than we can right now.
I would imagine a more likely solution is, wormholes either can't exist or can't transmit information.
> The best physical theory we currently have admits the existence of wormholes.
Just because the maths says it can exist in one set of equations, doesn't mean it can/does exist in our universe, especially lacking any evidence.
I'm not saying to stop researching the idea, but anyone sensible knows the outcome.
They will not be possible not matter how much you want them to be true. Just because something can exist doesn't mean it's either likely or not crazy.
This would contradict known physics. Again, please provide a better solution.
> Just because the maths says it can exist in one set of equations
That "one set of equations" is everything we know about the universe.
> but anyone sensible knows the outcome.
You mean like Kip Thorne, Leonard Susskind, Mat Visser, David Deutsch, and any other physicist who's studied wormholes? Because all those people agree that either we're wrong about physics or wormholes are theoretically possible. Causality violation, probably not, but wormholes don't violate causality just by existing.
> They will not be possible not matter how much you want them to be true
I have no strong opinion one way or the other. However, I accept that, based on the best physical theories we have available to us, wormholes are physically viable.
It seems like, for some reason, you really want them to be false. Perhaps it's your sense of "sensibility", which does not appear to be based in fact (unless you know something physicists don't).
It might piss the purists off to think like this but tough luck this is how the world works.
You seem happy to throw out causality? but not the faster than light bit. This seems biased.
Nope, going faster than light violates causality. As I have said N times, wormholes do not allow you to go faster than light. I really can't be any clearer on that. What they do is alter the topology of space so that you can create a shorter route between two locations that used to be "far away" in the old topology.
do you have any interesting read about the topic ?
Quantum particles decay and change and do stuff to each other and to understand it you need an equation to explain that, but some of those equations require the state of those decayed particles to provide their state to earlier parts of the equation, before they were created through quantum decay or their state determined by waveform collapse. This is sometimes described as time travel but it's not really, time has no relevance at that level of understanding. WE live in space-time and quantum physics is the foundation of that fabric. So the solution doesn't really violate the laws of time, it happens in a place where space and time don't have the same relevance.
If you somehow did create a feedback loop in this situation we'd never know. The concepts of it taking forever or being instantaneously resolved don't apply, because as far as we're concerned we only get the end product. We're not even sure of coherence is a good way of telling how much work has been done in a twisty, strange quantum problem like that.
I mention coherence because at the quantum level it's the only way of knowing which direction everything is happening in. It's not the same as time, but it's a bit more like very very fast entropy at a quantum level.
All of these things come together to give you space-time.
So when we talk about wormholes we're talking about the transmission of information on a quantum level, not a feature of space-time. The space and time parts are only relevant later.
No, they're actually not. https://en.wikipedia.org/wiki/Wormhole
General relativity admits traversable (i.e. macroscopic) wormholes. This is what we're discussing.
> you need an equation to explain that
Which equation? Schroedinger? The SE has time as a variable and doesn't do any of the "time travel" stuff you're talking about, so you must be referring to something else.
Where do you get the idea that time travel is crazy? Wormholes and the implications come from solid math (from what I understand).
Given that, GR and wormholes seem more similar than not.
The paper bending, sticking a pencil through explanation
is science fiction.
It's entirely unclear why you believe this would be impossible if our observable 4D universe is curved and embedded in one or more additional spatial dimensions.
They are a mathematical curiosity, not a thing that could actually exist.
If you could rewrite the laws of physics there are lots of cool things you could do, wormholes would just be the start......
Wormholes are more than likely impossible because to hold one open for travel, you would need some sort of negative matter/negative energy. That isn't forbidden by physics, but it's unlikely that it exists since we haven't seen any. Without negative energy/matter to hold a wormhole open, even if you could create one, just a single proton or electron would cause the wormhole to become unstable and collapse in on itself, and doing so faster than the proton could travel through.
No, it does not. See my more detailed reply here: https://news.ycombinator.com/item?id=12301781
Say you are in a gravity well with one side of the wormhole, and the other side is outside the well.
You could "lift" matter outside the gravity well without spending energy.
There are other problems as well: Gravity has no discontinuities, as objects move, the gravitational field moves with it. You never have a situation where gravity just suddenly shows up. (The same is true for an electrical field BTW - you can never create one, you can only move an existing one (i.e. split up the positive and negative parts). A magnetic field can be created, but that's because you always create a north and south at the same time. If magnetic monopoles existed you could not create just one, you could only separate the two halves.)
Anyway, a wormhole would allow you to have a gravitational discontinuity and that's impossible, it would create a gravitational wave with an infinite frequency. As you know a true square wave is physically impossible - the fourier transform requires an infinite frequency - but that's what you are doing by moving matter via a wormhole.
A wormhole is in no way a gravitational discontinuity, the toplogy for them is well defined. The creation of a wormhole would be a bit tricky, as this does require a discontinuity, but there's no reason to think that's impossible. After all, a gravitational singularity is also a discontinuity, and physicists have no problem with that.
Here's a concrete example:
https://en.wikipedia.org/wiki/Ellis_wormhole
That's a wormhole with a well-defined metric that satisfies the Einstein field equations.
That would be even worse, I replied to the same thing here: https://news.ycombinator.com/item?id=12301858
> A wormhole is in no way a gravitational discontinuity
A movable one certainly is, and a non movable one doesn't make any sense from a relativity point of view.
> Ellis Wormhole
Did you read your own link? "and there is no gravity"
There's a reason they say that. And there is no place in the universe without gravity. It's a mathematical solution, not a representation of the physical world.
The "no gravity" line there means the stress tensor is zero, and this is a so-called "vacuum solution." Essentially all closed form solutions to the field equations are vacuum solutions because it's almost impossible to write a closed form solution otherwise.
Sorry. The gravitational field of the object you just sent through the wormhole, not the gravitational field of the wormhole itself.
Do you agree that you can't "leave the universe" in the sense of travelling past the information-propagation wavefront of the Big Bang—even in a case where our universe begins to shrink and that wavefront starts to come toward us?
If yes, then a non-movable wormhole can be justified exactly like that: it's part of that same wavefront—part of the topological outer surface of the universe, not an object "in" the universe.
How is that? Wouldn't the gravitational force just propagate across the wormhole, making for a continuous gravitational gradient?
Maybe we're talking about separate conceptions of what a "wormhole" is here. For one example of what I'm picturing, you could have a one-wormhole universe as a three-dimensional hologram along the surface of a 4D hypertorus. You can go "through the doughnut hole" to get somewhere quicker than you could by going "around the doughnut", but that doesn't mean that there's a discontinuity anywhere on the surface of the hypertorus. Gravitational waves from one point-source would be propagating both "into" the wormhole (along the inside of the doughnut) and "through regular space" (along the outside of the doughnut) and eventually encountering themselves at the destination and maybe constructively or destructively interfering, but they wouldn't be forced into a square wave at any point.
That would be even worse. Let a strong gravitational force go through the wormhole and drop something near it (not through it).
Then move the wormhole (and the gravitational force) elsewhere, lift the object, and bring the wormhole back.
Normally the thing that generates gravity has inertial mass, so it costs energy to move. Not with a wormhole. If you speculate that it should have inertial mass, then how much?
Is this a thought experiment you came up with on your own, or do you have a paper you're citing? If the latter, do you have a link?
That would be even worse. Let the strong gravitational force of the Earth go through a wormhole located on a small platform in deep space, and drop a rock near the wormhole (not through the wormhole).
Then move the wormhole (and the gravitational force) elsewhere, lift the rock off the platform, and bring the wormhole back.
I would think that whatever method you have of moving a mouth of the wormhole, would have some interactions with the masses providing the gravitation.
Also, I'm not 100% sure that a wormhole would not have something like an inherent mass, because iirc there are solutions where a black hole mass is entirely because of the way spacetime is set up, without any particles needed? I'm not sure about that, but I think that is what I read..
But that's not what people mean when they say wormhole.
The ultraviolet example is the opposite: The universe acted in a certain way, so we looked for math to match, which happened to have a strange property to it.
Here first we found the strong property and are looking for the universe to match.
You can do the first, but not the second.
The Higgs boson also comes to mind.
Then explain how you conserve energy when you move an item out of a gravity well via a wormhole.
Or the even bigger problem I explain here: https://news.ycombinator.com/item?id=12301781
Consider an obvious example: a wormhole which connects two points on earth separated by 1m of real distance, at the same height.
Theres no violation of conservation of energy because you did not gain or lose gravitational potential energy, and your start and end momentum is conserved.
https://en.wikipedia.org/wiki/Kip_Thorne#Wormholes_and_time_...
Wormholes for matter and energy are not incompatible with physics. We just probably won't ever see one like the one he proposed, because creating it would require manipulation of matter or gravity at extreme scale.
But, it is wrong to say it is impossible. It is theoretically possible.
What's there to argue with? He doesn't claim wormholes can exist.
> because creating it would require manipulation of matter or gravity at extreme scale.
Not extreme scale, using a type of energy that doesn't actually exist. i.e. it's not about the quantity of energy, it's the type. It's a mathematical result, not an actual thing.
> But, it is wrong to say it is impossible. It is theoretically possible.
No, it is not possible. See my other replies in this thread.
"...calculations in semiclassical gravity suggest that quantum effects may be able to violate this condition in curved spacetime. Although it was hoped recently that quantum effects could not violate an achronal version of the averaged null energy condition, violations have nevertheless been found, so it remains an open possibility that quantum effects might be used to support a wormhole."