EDIT: Here is the lecture I'm referring to: https://www.youtube.com/watch?v=nEDFh8ma9zM
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.
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?
Edit:Lol, someone else also had this link as a reply to a similar thought.
doesn't our universe expand at the same speed?
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.
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.
Astronomers in different galaxy clusters will agree that each sees a set of cosmological horizons, but do not agree on where it is and what's inside it.
Schematically:
th<--g1<--<--yh--Them<--->You-->th-->g2-->yh
Every point in an expanding universe has its own set of cosmological horizons non-identical to its neighbouring points, and dramatically different from points at great distances in spacetime (that goes for great gaps in time at the same spacelike location, and great gaps in space at the same lookback time or scale factor).
For astrophysical black holes, a black hole horizon localizes around a particular clump of matter, and not around other nearby clumps of matter. Far from a super-dense clump of matter you will not find an astrophysical black hole horizon (barring primordial black holes, for which there is no evidence anyway).
Cosmological horizons focus on each infinitesimally small clump of matter, everywhere in the universe, even in deep extragalactic space where matter is extremely sparse. Indeed, even matter-free points have their own cosmological horizon, and we do have substantial evidence supporting that.
A theoretical black hole horizon arises in a family of solutions of the Einstein Field Equations, from exact ones like Schwarzschild or Kerr, to solutions that become those asymptotically (in the limit as a black hole formed by gravitational collapse ages, for example -- Schwarzschild and Kerr are eternal black holes that are never in an uncollapsed state).
A cosmological horizon arises in a different family of solutions of the Einstein Field Equations, from exact ones like the de Sitter vacuum or the expanding Robertson-Walker vacuum, to solutions that become those asymptotically (these are vacuum matter-free solutions, and one can get there with a solution with matter that dilutes away over time).
The two families of solutions are very different, although there is an overlap of solutions for black holes in expanding spacetimes, where there can be both a black hole horizon (or horizons) and a cosmological one (or more than one).
We can compare these different families of solutions most strikingly using the behaviour of test particles scattered through the spacetimes: near the BH event horizon particles may be entrained into stable circular orbits around the horizon of a theoretical black hole like Schwarzschild or Kerr, whereas this never happens around a cosmological horizon in a solution like de Sitter or expanding Robertson-Walker: the test particles all plunge right through the observer's horizon radially.
Once through the BH horizon a test particle will inevitably and very quickly by its own "wristwatch" collide with the gravitational singularity after passing through extremely curved spacetime. Our galaxy cluster has already passed through many cosmological horizons centred on distant galaxies who are now outside our horizon too. Neither our galaxy cluster nor the many distant ones have changed their essentially exclusive time-like trajectories, and there is no evidence we are soon going to end up colliding with a gravitational singularity. (Current evidence doesn't suggest we are going to end up facing a big rip either).
Now, in the cosmological model under time reversal galaxy clusters do tend to converge and naively collide and collapse into a singularity eventually. However, galaxies all plunge into it radially and matter does not get entrained into any sort of accretion disc or similar structure. (They disintegrate into clouds of gas and dust that heat up into the "un-recombination" surface of ionizing atoms (mostly hydrogen) which gets denser and hotter until neutrons and protons disintegrate, electroweak symmetries emerge, and so on, all at once. Black holes usually get to swallow clumps of matter from time to time, whereas the time-reversed big bang singularity gets everything landing on it all at once, rather than some clumps early, and some clumps earlier still).
Physically realistic models built on these theoretical systems are grossly different; the models are good for predicting future things in our sky, so we expect the astrophysical reality is different too.
The rough similarities tend not to survive real inspection. Different horizons are different in a bunch of ways that aren't overcome by the few ways in which they are somewhat similar (or similar under time-reversal).
Spatial discontinuities? Can you tell us more, please?
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.
I'd suggest clarifying this statement because it certainly gave me the wrong impression…
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.)
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.
Yes, and as humans are to plants, so our space faring descendents will be to us.
http://www.fhi.ox.ac.uk/wp-content/uploads/intergalactic-spr...
I'd be pretty surprised if the jump between galactic groups is much worse.
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).
Not so much.
https://www.youtube.com/watch?v=LTJauaefTZM
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.)
Your related comment says that m_{relativistic} is a pedagogical fiction. No, it is just a quantity that is non-identical to m_{0}. That students frequently forget (or do not know) that is a teaching failure.
However, you've introduced a gravitational event horizon, which is not something you can find in Special Relativity (whose spacetime is everywhere non-curved, that is, it is free of any gravitational effects at all).
If we pick out the globally flat background of Special Relativity and drop a test particle into it -- electrically neutral, low mass, and classically pointlike -- the latter generates the stress-energy tensor. Dropping indices and factors, G=T=0 -> G=T!=0, where G is the Einstein curvature tensor and T is the stress-energy tensor.
The stress-energy tensor is generally covariant: observers anywhere in spacetime, no matter how they are moving, agree on the total value of T at the point occupied by our test object. However, they are free to disagree on the quantities in the components of the stress-energy tensor.
The components of T can be written as a 4x4 matrix representing the flux of row-momentum into the column-direction. If (row,column) specifies a component of this matrix, and we count rows and columns 0..3, and we specify that our spacetime dimensions run 0...3 with 0 being the timelike dimension t, then a positive value of T (remember at a specific point in spacetime) in (0,0) and zeroes in all the other components means that momentum from the past of that point is flowing in the future of that point.
If at point p = (0,0,0,0), T^{00} = 1 and all the other components of T are zero, then at p' = (1,0,0,0), T^{00} = 1.
From Noether, a quantity that is invariant in time is conserved like the Newtonian conservation of energy.
An observer moving with our test particle generating T^{00} = 1 would relate the T^{00} quantity to the particle's rest mass (or invariant mass, if you like).
Let's call our 1 rows and columns "x" after the Cartesian direction
On a spacetime diagram, our test particle develops a worldline vertically along the t axis and not at all along the x axis.
Now let's complicate this a bit by having the test particle chuck a bit of itself out its back, engaging a classical notion of conservation of momentum. We'll call the 1 dimension backwards-and-forwards, or x, compared to our timelike 0 axis t. T^{01}, if positive, encodes the momentum coming from the past and leaving the point in the forwards direction.
Assuming coordinates (t,x,y,z) that absorb the emitted units:
At p = (0,0,0,0) we have T = 1, and T^{00} = 1.
Let's keep things normalized so that our particle is always at the origin of x.
At p' = (1,0,0,0) we have T = 1, and T^{00} = 0.9 and T^{01} = 0.1.
At P = (2,-1,0,0) we have the boosted exhaust: T^{01} = 0.1; at p'' = (2,0,0,0) we have the particle T^{00} = 0.9. Thus at p''' = (3,0,0,0) we have the particle still T^{00} = 0.9, and the exhaust P'' = (3,-2,0,0), T^{0,1} = 0.1.
But notice that this picture depends on coordinate conditions: the "rocket" particle at x=0 always, tracing out a vertical worldline on a spacetime diagram. The exhaust does not remain at x=0, and so traces out a worldline that has an angle from vertical.
If we flip this so the exhaust is at x=0, then we would say that the exhaust is at P = (2,0,0,0), P'' = (3,0,0,0) etc and its |T^{00}| remains 0.1 and it traces out a vertical worldline on the spacetime diagram. The "rocket" on the other hand is at p'' = (2,1,0,0), p''' = (3,1,0,0) etc and its |T^{01}| is 0.9.
What component(s) stress-energy appears in depends on the choice of coordinate basis.
Likewise, if we draw a spacetime diagram with the exhaust always at x=0, it traces a vertical worldline up the t axis, while the "rocket" traces out a worldline at some angle, because it is not at a constant x coordinate.
A completely different observer holding itself at x=0,y=0,z=0 would calculate different coordinate-values for particle/rocketing-particle/exhaust (changing the coordinates of p, p', p'', ... and P, P', .... However, it would agree that a normalized value of the whole T at p and p' is 1 but that the value of T at p'' is 0.9 while the value of T at P is 0.1. However, the total of 1, 0.9, or 0.1 respectively could be allocated to different components of T in 4x4 matrix form.
Technically, since T is nonzero at several points in spacetime (all those p and P points) spacetime is not flat. However, in any timelike hypervolume of this nearly empty spacetime, the total stress-energy will be 1.
Even if we move the "rocket" and its exhaust apart ultra-relativistically, the sum of their stress-energies at any time will remain 1. In Newtonian terms, what's being described is a total conservation of energy, and an unchanging centre-of-mass in a deforming system. Your rocket/bussard is similar: there is a system of ship + fuel + exhaust (+ waste heat + ...) whose observer-independent (or generally covariant) total is constant at any time. Thinking in a more field-like way, there are rocket-bits, fuel-bits, exhaust-bits (etc) which generate nonzero stress-energy at various points in the spacetime. The stress energy at each point in spacetime can be agreed by all observers, however they are free to disagree about how the stress-energy at a point is distributed among the various tensor components.
In order to form an event horizon we would need a much larger quantity of stress-energy in a small region, and that is not what is described in your posting, which is more about extremizing components of the tensor (at various points) rather than the whole tensor itself.
Uh, I think it's the other way around: the energy you pump in becomes additional mass.
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.
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.
Find a way to decompose an individual's personality into progressively more granular dimensions of behavior. Model stimulus -> response reactions as transformations. Sample enough responses from each type of behavior, make linear approximations of the transformations until you achieve a 1:1 simulacra, and derive a basis for the response basis. Your human mind will be a matrix representation of the map between the stimulus and response spaces.
As unrealistic as all of that sounds, it still sounds significantly easier to me than uploading (or even interfacing with) a mind.
On the other hand while uploading minds probably has some issues, it involves replicating thing that we can assume resides in physical space, the question remains as to how and whether at all we can measure the internal structure with sufficient accuracy and whether such measurement is nondestructive.
And in the end, problem of somehow interfacing with an mind can mean many things which range from solved issue (when typing this comment counts as "interfacing") to something that for me seems like purely engineering issue (building new neural attached "peripherals" for the brain or emulating existing ones)
For a basic example off the top of my head, consider a hash function. A hash function h : {0, 1}^' --> {0, 1}^n is not actually* injective (it can't be, since the domain is effectively infinite-dimensional and the codomain is finite-dimensional). However, cryptographic security mandates that it should be infeasible to find a preimage message for any digest in the codomain. Moreover messages with very small differences in the domain should be mapped to digests with very large differences in the codomain. This artificial noise and complexity doesn't resemble human reactions whatsoever; it's fairly easy to say two things which will each elicit your regional-specific greeting. In general many human responses have common triggers, and I would further conjecture that you could categorically simplify this further by reducing human responses to broader equivalence classes based on language, geographical region, mood, etc.
This is not to say it isn't challenging. I would expect building a linear approximation of a human mind using input -> output mappings to be extraordinarily difficult. But it's not artificially difficult, like well-designed cryptography. Breaking well-designed cryptography is intended to be, in a mathematical sense, a maximally difficult endeavor - much more difficult than basically anything else you can possibly do in nature.
More to my original point you and I can at least entertain a coherent conversation about building a matrix representation of a human mind using finite stimulus and response spaces. We're in familiar territory, even if it's not ultimately possible or feasible. It's mathematically sound to approach this, given a few well-defined assumptions.
In contrast, I don't know (nor am I confident anyone else knows) how to 1) replicate a human mind via as of yet nonexistent direct brain-interface technology, or 2) how to upload a human mind, using even more nonexistent technology so as to preserve continuity of consciousness. Not only are there rampant unknowns unknowns involved in the engineering efforts entailed here, there are unresolved questions and rampant philosophical disagreements in the fundamental assumptions. We're not in familiar territory here.
I’d say this is an engineering problem, rather than #2, which is philosophical. For #1, all you really need is to measure all brain cells accurately enough, then recreate the whole thing in a simulation. Could probably be achieved with nanobots or very advanced scanners within couple of centuries. Might be acceptable to destroy the original in the process, if it makes it more feasible.
Some (most?) people have a rich internal world which can never be caught by looking at I/O relations.
Also, do you believe that by asking e.g. a person like Albert Einstein a reasonable amount of questions (an amount that a person can answer without getting seriously annoyed or fatigued), you would be able to reconstruct their problem solving skills? Sounds unlikely to me.
That being said I think your second challenge is more interesting. Albert Einstein's achievements are the product of both extreme knowledge/specialization, his experience and his personality. I think you'd likely have to have a "knowledge space" which can be mapped to the human "mind matrices." That does complicate things a fair bit, but in the abstract I think a "vanilla human" could plausibly be seeded with Einstein's personality and as much knowledge as you want.
How do we know that the incomprehensibly weird and advanced minds running our ships and habitats in those unimaginably distant points of space and time won't just decide that virtual smiley faces with our names written on them are close enough to, "it remains you." How do we know they won't one day do a "slightly lossy compression" of the human race?
If you transform rather than duplicate yourself, it doesn't matter if you're still 'human'. What matters is that you're alive and conscious.
We don’t even know where to start replacing our bodies. AI? Genetics? Cybernetics?
I am not sure of this. Even if we pooled the Earth's resources into constructing a generation ship, we still are not sure we are capable of making a ship that is sustainable both socially and technologically.
We do not know if our tech can last hundreds of years. Even if that wasn't the problem, we do not know if we can maintain a self-sustaining environment that lasts hundreds of years. Even if that wasn't the problem, we don't know what failure modes need to be accounted for. Even if that wasn't the problem, we don't know how to keep humans sane on such a journey. It is, after all, unethical to have new humans born on a journey they never signed up for. We do not have the right to determine the fate of our progeny.
An upload to a synthetic medium is perhaps the only sane and ethical way to accomplish this goal.
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.
"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.
Also, there are theories of FTL: https://en.wikipedia.org/wiki/Faster-than-light
Ah, no they didn't. Scientific consensus has been the earth is round for thousands of years.
I'm not arguing with your idea ... just that it should start with a caveat ... "there are no current theories that support FTL but we're hoping ..."
However, if the idea is that a laser that is continuously lit can "sweep" a path, such that the laser dot appears to move faster than light could travel that same path... Then of course that's trivially true. The light is traveling the radius of the arc, not the length.
Sure, this is correct, but I don't see how this describes anything traveling faster than light. The light spot itself is an effect of the light that's traveled to that point (at the speed of light). The spot "moving" is (physically) more of an illusion as the light now travels to an adjacent location.
As far as I understand it doesn't actually move
The light itself will continue to travel at normal speed but if you waited for the light to bounce back from distant planets you could observe the shadow moving FTL.
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.
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.
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)
Could you elaborate?
Edit:
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 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.
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.
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.
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.
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.
Both are important tools for making predictions tractable.
But when we lose sight of what are conclusions, what are strongly justified assumptions, and what are simplifying assumptions we don’t have justification for (or even know to be untrue), we begin to create fundamentally inaccurate models or wrongly shut down others’ avenues of inquiry.
This happens in economics and business quite often, but simplifying assumptions become orthodox truth with surprising frequency in hard sciences like physics, as well.
"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?