People keep asking what I think about Christopher Nolan’s new film ‘Interstellar.’ The answer is that I haven’t seen it yet, but plan to early next week. Some of the attendees of the Tennessee Valley Interstellar Workshop were planning to see the film on the event’s third day, but I couldn’t stick around long enough to join them. I’ve already got Kip Thorne’s The Science of Interstellar queued up, but I don’t want to get into it before actually seeing the film. I’m hoping to get Larry Klaes, our resident film critic, to review Nolan’s work in these pages.
Through the Wormhole
Wormholes are familiar turf to Al Jackson, who spoke at TVIW on the development of our ideas on the subject in science and in fiction. Al’s background in general relativity is strong, and because I usually manage to get him aside for conversation at these events, I get to take advantage of his good humor by asking what must seem like simplistic questions that he always answers with clarity. Even so, I’ve asked both Al and Marc Millis to write up their talks in Oak Ridge, because both of them get into areas of physics that push beyond my skillset.
Al’s opening slide was what he described as a ‘traversable wormhole,’ and indeed it was, a shiny red apple with a wormhole on its face. What we really want to do, of course, is to connect two pieces of spacetime, an idea that has percolated through Einstein’s General Relativity down through Schwarzchild, Wheeler, Morris and Thorne. The science fiction precedents are rich, with a classic appearance in Robert Heinlein’s Starman Jones (1953), the best of his juveniles, in my opinion. Thus our hero Max explains how to get around the universe:
You can’t go faster than light, not in our space. If you do, you burst out of it. Buf it you do it where space is folded back and congruent, you pop right back into our space again but it’s a long way off. How far off depends on how it’s folded. And that depends on the mass in the space, in a complicated fashion that can’t be described in words but can be calculated.
I chuckled when Al showed this slide because the night before we had talked about Heinlein over a beer in the hotel bar and discovered our common admiration for Starman Jones, whose description of ‘astrogators’ — a profession I dearly wanted to achieve when I read this book as a boy — shows how important it is to be precisely where you need to be before you go “poking through anomalies that have been calculated but never tried.” Great read.
If natural wormholes exist, we do have at least one paper on how they might be located, a team effort from John Cramer, Robert Forward, Michael Morris, Matt Visser, Gregory Benford and Geoffrey Landis. As opposed to gravitational lensing, where the image of a distant galaxy has been magnified by the gravitational influence of an intervening galaxy, a wormhole should show a negative mass signature, which means that it defocuses light instead of focusing it.
Al described what an interesting signature this would be to look for. If the wormhole moves between the observer and another star, the light would suddenly defocus, but as it continues to cross in front of the star, a spike of light would occur. So there’s your wormhole detection: Two spikes of light with a dip in the middle, an anomalous and intriguing observation! It’s also one, I’ll hasten to add, that’s never been found. Maybe we can manufacture wormholes? Al described plucking a tiny wormhole from the quantum Planck foam, the math of which implies we’d have to be way up the Kardashev scale to pull off any such feat. For now, about the best we can manage is to keep our eyes open for that astronomical signature, which would at least indicate wormholes actually exist. The paper cited above, by the way, is “Natural Wormholes as Gravitational Lenses,” Physical Review D (March 15, 1995): pp. 3124-27.
Enter the Space Drive
To dig into wormholes, the new Thorne book would probably be a good starter, though I base this only on reviews, as I haven’t gotten into it yet. Frontiers of Propulsion Science (2009) also offers a look into the previous scholarship on wormhole physics and if you really want to dig deep, there’s Matt Visser’s Lorentzian Wormholes: From Einstein to Hawking (American Institute of Physics, 1996). I wanted to talk wormholes with Marc Millis, who co-edited the Frontiers of Propulsion Science book with Eric Davis, but the tight schedule in Oak Ridge and Marc’s need to return to Ohio forced a delay.
In any event, Millis has been working on space drives rather than wormholes, the former being ways of moving a spacecraft without rockets or sails. Is it possible to make something move without expelling any reaction mass (rockets) or in some way beaming momentum to it (lightsails)? We don’t know, but the topic gets us into the subject of inertial frames — frames of reference defined by the fact that the law of inertia holds within them, so that objects observed from this frame will resist changes to their velocity. Juggling balls on a train moving at a constant speed (and absent visual or sound cues), you could not determine whether the train was in motion or parked. The constant-velocity train is considered an inertial frame of reference.
Within the inertial frame, in other words, Newton’s laws of motion hold. An accelerating frame of reference is considered a non-inertial frame because the law of inertia is not maintained in it. If the conductor pulls the emergency brake on the train, you are pushed forward suddenly in this decelerating frame of reference. From the standpoint of the ground (an inertial frame), you aboard the train simply continue with your forward motion when the brake is applied.
We have no good answers on what causes an inertial frame to exist, an area where unsolved physics regarding the coupling of gravitation and inertia to other fundamental forces leave open the possibility that one could be used to manipulate the other. We’re at the early stages of such investigations, asking whether an inertial frame is an intrinsic property of space itself, or whether it somehow involves, as Ernst Mach believed, a relationship with all matter in the universe. That leaves us in the domain of thought experiments, which Millis illustrated in a series of slides that I hope he will discuss further in an article here.
Fusion’s Interstellar Prospects
Rob Swinney, who is the head of Project Icarus, used his time at TVIW to look at a subject that would seem to be far less theoretical than wormholes and space drives, but which still has defeated our best efforts at making it happen. The subject is fusion and how to drive a starship with it. The Daedalus design of the 1970s was based on inertial confinement fusion, using electron beams to ignite fusion in fuel pellets of deuterium and helium-3. Icarus is the ongoing attempt to re-think that early Daedalus work in light of advances in technology since.
But like Daedalus, Icarus will need to use fusion to push the starship to interstellar speeds. Robert Freeland and Andreas Hein, also active players in Icarus, were also in Oak Ridge, and although Andreas was involved with a different topic entirely (see yesterday’s post), Robert was able to update us on the current status of the Icarus work. He illustrated one possibility using Z-pinch methods that can confine a plasma to heat it to fusion conditions.
Three designs are still in play at Icarus, with the Z-pinch version (Freeland coined it ‘Firefly’ because of the intense glow of waste heat that would be generated) relying on the same Z-pinch phenomenon we see in lightning. The trick with Z-pinch is to get the plasma moving fast enough to create a pinch that is free of hydrodynamic instabilities, but Icarus is tracking ongoing work at the University of Washington on the matter. As to fuel, the team has abandoned deuterium/helium-3 in favor of deuterium/deuterium fusion, a choice that must flow from the problem of obtaining the helium-3, which Daedalus assumed would be mined at Jupiter.
Freeland described the Firefly design as having an exhaust velocity of 10,000 kilometers per second, with a 25 year acceleration period to reach cruise speed. The cost: $35 billion a year spread out over 15 years. I noted in Rob Swinney’s talk that the Icarus team is also designing interstellar precursor missions, with the idea of building a roadmap. All told, 35,000 hours of volunteer research are expected to go into this project (I believe Daedalus was 10,000), with the goal of not just reaching another star but decelerating at the target to allow close study.
Image: Artist’s conception of Icarus Pathfinder. Credit: Adrian Mann.
Let me also mention a design from the past that antedates Daedalus, which was begun in 1973. Brent Ziarnick is a major in the US Air Force who described the ARPA-funded work on nuclear pulse propulsion that grew into Orion, with work at General Atomics from 1958 to 1965. Orion was designed around the idea of setting off nuclear charges behind the spacecraft, which would be protected by an ablation shield and a shock absorber system to cushion the blasts.
We’ve discussed Orion often in these pages as a project that might have opened up the outer Solar System, and conceivably produced an interstellar prototype if Freeman Dyson’s 1968 paper on a long-haul Orion driven by fusion charges had been followed up. Ziarnick’s fascinating talk explained how the military had viewed Orion. Think of an enormous ‘battleship’ of a spacecraft that could house a nuclear deterrent in a place that Soviet weaponry couldn’t reach. At least, that was how some saw the Cold War possibilities in the early years of the 1960s.
The military was at this time looking at stretch goals that went way beyond the current state of the art in Project Mercury, and had considered systems like Dyna-Soar, an early spaceplane design. With a variety of manned space ideas in motion and nuclear thermal rocket engines under investigation, a strategic space base that would be invulnerable to a first strike won support all the way up the command chain to Thomas Power at the Strategic Air Command and Curtis LeMay, who was then Chief of Staff of the USAF. Ziarnick followed Orion’s budget fortunes as it ran into opposition from Robert McNamara and ultimately Harold Brown, who worked under McNamara as director of defense research and engineering from 1961 to 1965.
Orion would eventually be derailed by the Atmospheric Test Ban Treaty of 1963, but the idea still has its proponents as a way of pushing huge payloads to deep space. Ziarnick called Orion ‘Starfleet Deferred’ rather than ‘Starflight Denied,’ and noted the possibility of renewed testing of pulse propulsion without nuclear pulse units. The military lesson from Orion:
“The military is not against high tech and will support interstellar research if they can find a defense reason to justify it. We learn from Orion that junior officers can convince senior leaders, that operational commanders like revolutionary tech. Budget hawks distrust revolutionary tech. Interstellar development will be decided by political, international, defense and other concerns.”
Several other novel propulsion ideas, as well as a book signing event, will wrap up my coverage of the Tennessee Valley Interstellar Workshop tomorrow.
@Alex: The limit v –> c you mention is just what I also mentioned: The photon rocket. Because it does not carry propellant, it is indeed the space drive we seek. Exemplified by the flashlight (actually fairly efficient as photon rockets go), it is just way too weak to be useful given any power source we have. Any space drive producing more thrust per Watt would inevitably run into the perpetual motion problem brought up above. I do not see how to get out of this without dropping some very fundamental tenets of physics.
@Rob: I am not familiar with the ‘experience of spacetime’ thing, it sounds a bit wacky to me. If you can extract energy from the vacuum (by definition impossible) or dark matter (the purest of speculation), then you are right: Who needs perpetual motion.
@Eniac – I think we can agree that conservation of energy cannot be violated. All we disagree on is whether your formulation “proves” that the Woodward effect is bogus. I don’t think it does. If it did, I think that this would have been pointed out by a lot of physicists by now.
Your flashlight example is valid, although in practice it won’t go very fast at all. A solar sail is much more efficient and practical. The Woodward effect, if real, may not be as efficient as a solar sail, but it may be more efficient than a chemical or nuclear rocket. That would potentially be a game changer for deep space missions requiring high velocity, as the propellant mass would be reduced to just that needed to power the engines, rather than accelerate its own mass. Woodward would have to show an unambiguous effect, as well as some indication about efficiency before I was convinced that the effect was a) real and b) that it had a role to play in propulsion. I think he is definitely in “extraordinary claims needing extraordinary proof” territory.
@Eniac a flashlight or photon rocket does have a reaction mass. We can use a laser as an example. Light waves or photons come off the back end which results in pushing the rocket forwards. Think about Newton’s third law of motion. A warp drive does not have a reaction mass for example.
A photon rocket will work but it takes longer for it due to the fact that light has not mass but it must be limited to subluminal or sublight speeds since it has a reaction mass.
A photon rocket takes a longer time to accelerate since light has no mass but it has energy so it will accelerate given enough time.
@Geoffrey Hillend November 29, 2014 at 19:50
‘A warp drive does not have a reaction mass for example.’
If space is compressed in front of the craft and expanded behind is it any different to a compressor used in a rocket engine, so space-time which contains vacuum energy must be the reaction mass. So a warp drive should be a reaction drive by comparison.
@Alex:
When you say “… would be reduced to just that …” you are implying that the propellant mass is higher than that of the fuel, or that it is separate. In an efficient rocket, however, that is not the case. Chemical rockets are very efficient in the sense that the propellant mass exactly equals that of the fuel, i.e. the propellant consists of ONLY the waste products of energy production. Other examples of this would be fission fragment rockets, where the waste product of fission is used as propellant, and the anti-matter photon rocket. Neither of these systems could be improved by making them reaction-less while keeping the energy source the same. So, in my opinion, the whole reaction-less thing (in addition to violating fundamental physics), is also a red herring: The real problem with propulsion is not the propellant, but the power source. All means of power production that we know of have waste, which handily offers itself as propellant, for free.
Bogus or not, I do think it proves that if the drive could be made to produce more thrust per Watt than a flashlight, it would enable us to build a perpetual motion machine. This has been pointed out by physicists, and most would say it increases the likelihood of bogus.
Propulsion without a reaction mass only violates classical physics but not semi-classical special and general relativity which is what one must know to appreciate an Alcubierre Warp drive.
@Michael it isn’t just as simple as expansion and contraction. Space itself is being expanded and contracted which is different than the pressure of expanding plasma in a combustion chamber. The normal space bubble is being pushed in back and pulled in front simultaneously. The occupants inside the spacecraft don’t feel any inertial effects from the FLT and are weightless as the result of a free fall geodesic. There is a certain theory that is behind not based on ordinary physics. See diametric drive.
@Eniac – what I was trying to get at with regards to the rocket equation was the exponential increase in fuel/propellant to gain velocity, as the rocket must propel itself and the unused fuel. If we imagine a rocket that receives its fuel in some sort of beam/stream, then the craft can accelerate faster and attain a higher velocity for the same amount of fuel, albeit at the cost of the beamer accelerating the fuel to the craft. I see the Woodward effect as having a similar effect as the beam, the craft needs less fuel to attain a specific velocity than a conventional rocket. Now if that cannot be done because you are just converting fuel to power the drive, then it makes no sense as the craft still needs to accelerate the the same fuel mass as a rocket. Which is why I remain skeptical not just of the effect, but also of its usefulness as a drive. It only makes sense if the effect has a performance impact that reduces the fuel/propellant needed for the rocket equation.
We also have to consider that there are other propulsion methods that have better performance than rockets, and that the Woodward Effect drive would have to compete with them too. It seems we are a lot farther forward with these other methods, which is where I would put my resources, although few offer the low cost access to space that we really need to bootstrap our civilization into space.
Now if we could create an inertialess drive, that would be something, however that clearly would be a perpetual motion machine and therefore impossible.
Wanna bet!
http://www.extremetech.com/extreme/168771-researchers-seemingly-break-newtons-third-law-create-optical-diametric-drive
@Geoffrey – I don’t understand that experiment from the article and I cannot read the original paper. If they can do what they say, then eventually the light pulse would be traveling faster than light in the fiber. Wouldn’t this result in Cerenkov radiation being emitted initially? After that the pulse would be traveling faster than light in vacuo? I’d like to see this result verified and put in context of relativity.
@Al Jackson
just one more comment concerning ‘Digital Apollo’; additionally, in the book. They pointed out that the visiting astronauts were given a series of in-depth lectures on inertial guidance platforms. The astronauts recounted that they were not too happy for these lectures, that they really only wanted to know which buttons were appropriate to push ! So while they were engineers for the most part they knew that the parts they would play would be mostly in the execution phase of their missions. Just thought you’d like to know that !
All that being said, Mr. Jackson may I suggest that perhaps should write a book on your connection with the manned space flight Center and your various observations of the astronauts at that time. I think it would be quite interesting all in all.
@Geoffrey – I don’t understand that experiment from the article , either. In fact I would say that this phenomenon has nothing to do with reaction-less forces, but some other phenomenon. Newton’s third law has been tested for over 400 years and it has always been shown to be true. The new phenomenon concerning general relativity, however, has to do as I understand it, with motion along shortest geodesics that are available in space-time. As I understand it, this is the essence of how the warp drive is supposed to work by creating these geodesics. I suppose then general relativity would be concerned with the closest thing we have to true non-Newton’s third law ideas.
@Alex Toley The photons in the diametric drive don’t go faster than the speed of light since they are limited to special relativity. There is Cherenkov radiation from fiber optics whether or not we use an optical diametric drive because Cherenkov radiation is the result of a slower velocity of light through a medium like air, water or fiber optics so C can be violated in such a medium but still be slower than C in empty space so C is not really violated.
@William Newton’s third law is still true but that does not me there is not a “loophole” in it. There may be a subtle a difference between a warp drive and a diametric drive but they both use negative energy. A warp drive drags its local space reference frame with it but a diametric drive does not do that in this case so it does not have to go faster than C. The important thing is it violates the second law of thermodynamics which states that an isolated system must loose energy due to entropy but the optical diametric drive doesn’t loose energy.
It also does not have a reaction mass so it in my opinion is a hint that the idea physics behind the idea of the diametric drive is sound and might work on the large scale if we can make some negative energy, mass etc. Consequently, there is hope such a device or spacecraft using a diametric drive could someday be built in the distant future.
I must admit that I don’t completely understand the physics of the optical diametric drive and I would like to see the paper on how it works in more detail.
Alex: I think we are on the same wavelength now. The “reactionless drive” is only advantageous if it uses less power than a rocket to get the same thrust. This however, also allows you to construct a perpetual motion machine, making it very hard to reconcile the drive with mass-energy conservation.
Things are a little bit different when the craft is not self contained during flight, i.e. receives energy or fuel (or reaction mass) from external sources. The open system equivalent to the flashlight is the solar sail, and the task for the space drive is to be more efficient than that using solar panels as an energy source. Not going to happen, IMHO, but, well, you never know….
January 21, 2015
In theory, the Milky Way could be a ‘galactic transport system’
Based on the latest evidence and theories our galaxy could be a huge wormhole (or space-time tunnel, have you seen “Interstellar?”) and, if that were true, it would be “stable and navigable”.
This is the hypothesis put forward in a study published in Annals of Physics and conducted with the participation of SISSA in Trieste. The paper, the result of a collaboration between Indian, Italian and North American researchers, prompts scientists to re-think dark matter more accurately.
“If we combine the map of the dark matter in the Milky Way with the most recent Big Bang model to explain the universe and we hypothesise the existence of space-time tunnels, what we get is that our galaxy could really contain one of these tunnels, and that the tunnel could even be the size of the galaxy itself. But there’s more”, explains Paolo Salucci, astrophysicist of the International School for Advanced Studies (SISSA) of Trieste and a dark matter expert.
“We could even travel through this tunnel, since, based on our calculations, it could be navigable. Just like the one we’ve all seen in the recent film ‘Interstellar'”. Salucci is among the authors of the paper recently published in Annals of Physics.
Although space-time tunnels (or wormholes or Einstein-Penrose bridges) have only recently gained great popularity among the public thanks to Christopher Nolan’s sci-fi film, they have been the focus of astrophysicists’ attention for many years.
“What we tried to do in our study was to solve the very equation that the astrophysicist ‘Murph’ was working on. Clearly we did it long before the film came out” jokes Salucci. “It is, in fact, an extremely interesting problem for dark matter studies”.
“Obviously we’re not claiming that our galaxy is definitely a wormhole, but simply that, according to theoretical models, this hypothesis is a possibility”. Can it ever be tested experimentally? “In principle, we could test it by comparing two galaxies – our galaxy and another, very close one like, for example, the Magellanic Cloud, but we are still very far from any actual possibility of making such a comparison”.
Full article here:
http://phys.org/news/2015-01-theory-milky-galactic.html
Why wormholes probably do not exist and our galaxy is not a giant transportation system:
http://galileospendulum.org/2015/01/26/why-wormholes-probably-dont-exist/
Starfleet was closer than you think
More than half a century ago, Project Orion offered the potential to open up the solar system with nuclear propulsion technologies, only to be shelved.
Brent Ziarnick and Peter Garretson discuss, based on recently declassified memos, that the Air Force was closer than previously believed in deciding to fund work on Orion.
Monday, March 16, 2015
http://www.thespacereview.com/article/2714/1
To quote:
Secretary McNamara’s and Dr. Brown’s conservatism and lack of vision has left humanity in a local minima, trapped in a gravity well, unable to access the vast wealth of the inner solar system, and left the life on our entire planet bare and defenseless against what has emerged as a credible threat: asteroids and comets.
We have traded the grand visions of 1962 for a much more tawdry reality, one where instead of going to space in ships with large crews that could roam the inner solar system in voyages measured in months, and would have laid the foundation for humans to reach other stars, our species has accepted small tin cans that may just be able to send a handful of specialists to Mars before the Apollo lunar landing centennial.
Had the US Air Force not been gelded in 1962, humanity would today be reaching for the stars.