by Paul Gilster | Feb 16, 2006 | Breakthrough Propulsion |
Those interested in reading the controversial paper by Franklin Felber recently presented at the STAIF meeting in Albuquerque can find it here. The summary is concise: “The Schwarzschild solution is used to find the exact relativistic motion of a payload in the gravitational field of a mass moving with constant velocity. At radial approach or recession speeds faster than 3-1/2 times the speed of light, even a small mass gravitationally repels a payload. At relativistic speeds, a suitable mass can quickly propel a heavy payload from rest nearly to the speed of light with negligible stresses on the payload.”
A first reading of the paper reveals an intriguing implication: Felber’s solutions of Einstein’s field equation imply that any mass produces what Felber calls an ‘antigravity field’ above a certain critical velocity. And although this field is at least twice as strong in the direction of motion, the field also repels particles in the opposite direction. It follows, quoting Felber again, that “…a stationary mass will repel masses that are radially receding from it at speeds greater than 3-1/2 c, with obvious cosmological implications.”
Is Felber suggesting a way of explaining Einstein’s cosmological constant, and thus accounting for the apparent acceleration in the universe’s expansion? An intriguing thought, though the equations that express it will demand long and patient scrutiny. Audacious papers make fascinating reading, but the road to experimental verification is unforgiving, as all too many researchers have learned.
by Paul Gilster | Feb 15, 2006 | Tau Zero Foundation |
by Ian Brown
Centauri Dreams’ discussions of a foundation to support research into interstellar flight caught the eye of Edinburgh-based science writer Ian Brown. As far as I know, the article that resulted is the first appearance of the new foundation in the mainstream media, and it is reprinted here with the permission of its author and The Scotsman, where it ran on February 4 of this year. Brown discusses the background and thinking behind the still unnamed foundation with Marc Millis, the group’s founding architect. We are very close to a final decision on the name, incidentally; Centauri Dreams will post that news as soon as it is finalized.
The staggering claims submitted in a scientific paper last month (see The Scotsman, January 5th) that we might be able to travel to alien star-systems in months rather than millennia were sensational enough to make the cover of New Scientist magazine.
Don’t plan that trip to Alpha Centauri just yet, though. The ‘hyperdrive’ – which would allow a spacecraft to take a shortcut through an extra dimension of space-time – is based on dauntingly abstruse equations by the late Burkhard Heim. A reclusive German physicist, Heim reads like a character out of Metropolis. Badly disabled in a laboratory accident in his teens, he first mooted the hyperdrive concept in 1957 but lapsed quickly back into obscurity (he died virtually forgotten in 2001). Bemused scientists reviewing the paper’s claims already complain they find much of his work incomprehensible.
But the hyperdrive has at least propelled the tantalising possibility of interstellar (as opposed to mere interplanetary) travel back into the headlines. Could we ever actually bridge the insane distances to the stars within human lifetimes?
NASA scientist Marc Millis, founder and former manager of the agency’s now defunct Breakthrough Physics Propulsion Project (BPPP), remains cautious. “The hyperdrive approach is in such an early stage of development that it is premature to judge its viability,” he warns. “Fortunately, relatively low-cost next steps could be taken by its proponents to help assess the prospects, such as confirming the ability of the Heim theory to predict the masses of sub-atomic particles, and showing the derivations and equations necessary to comprehend the other assertions.
“But it is important to remember that there are many other approaches out there,” he adds. “The best way to determine which of these might merit support is to conduct a competitive research solicitation.”
Millis established the BPPP in 1996 to do just that – act as a clearing house for research into identifying what future technologies just might one day make interstellar journeys possible. But three years ago NASA shelved it to focus its travel plans nearer to home (the Moon by 2018, Mars by 2050). Undaunted, Millis, and a network of collaborators he has built up, aim to launch a separate not-for-profit foundation this year to continue to promote such research.
“Interstellar flight broaches the possibility of finding another place on which to live so that our survival is not limited to one pale-blue dot in the cosmos,” explains Millis. “That has so many profound implications.”
Not least among them is the sheer enormity of what that challenge entails. Even light, travelling at 186,000 miles a second, takes over four years to reach just the nearest star to our own Sun. The Voyager space-probe, the fastest man-made object ever built, would take over 80,000 years to get there. No wonder many scientists think interstellar travel is a goal far too far.
“When it comes to travelling faster than light the challenge is indeed daunting,” agrees Millis. “There is plenty of physics to suggest that this is impossible, and the theories that challenge this limit all evoke time travel paradoxes. On the other hand, when it comes to the goal of a ‘space drive’ – a non-rocket breakthrough – there is no physics to say that it is impossible, but conversely, no proven physics yet to suggest how to achieve it.”
That’s where the proposed new foundation comes in. It will create a network of researchers amongst academia, industry, the military and government to explore the most promising candidate technologies. They will share information, review and critically assess each other’s work. “The immediate core already spans Belgium, Italy, Austria as well as the US,” Millis says. “I have not yet tapped into the deeper network of interstellar practitioners out there, including some in the UK.
“We won’t be able to offer research grants, however, until after we secure substantial philanthropic donations. So far we have one financial benefactor who is taking care of our start-up costs in addition to all the volunteer help from my network of professionals. We don’t yet have a sales-pitch document to seek serious funding. But the SETI (Search for Extra-Terrestrial Intelligence) institute is one model I’ve looked at.”
Possible names for the foundation include the Interstellar Propulsion Foundation, the Deep Future Foundation, the Centauri Foundation and the Blue-Shift Foundation. “One thing that we have adopted,” Millis says, “is the sub-title ad astra incrementis, which means ‘to the stars in steps, where each is larger than before’.”
Millis joined NASA in 1982. His earliest publication on interstellar propulsion was in 1990. “From there I started to encounter other like-minded researchers. That was the start of the group that led to this foundation.”
So what are the most promising candidates to propel Earth’s first starship? They range from near-term technology – light-sails, anti-matter, ion engines – to the seemingly fantastic -warping space-time (or ‘metric engineering’ in the new buzz-word) or tunnelling through wormholes. All are up for serious consideration.
“All of the options, even those based on technology we could launch today, have pros and cons,” Millis emphasises. “If the emphasis is on ‘cheap’ and ‘launch now’, with little regard for how long an interstellar probe will take to reach its destination, the clear winner is some form of solar-sail. If shorter missions or larger payloads are desired, the choices become more difficult. From here it breaks down into two branches; emerging technology, and undiscovered physics.
“The challenge with the emerging technology, which builds on known physics, is the ‘incessant obsolescence postulate’. This states that no matter when an interstellar probe is launched, it will be passed by a more modern probe launched later. The question then isn’t so much ‘can we’ but what are the most important design factors to work toward: cheap, available now, quickest trip, size of payload, etc?
“When it comes to undiscovered physics, where the intent is to circumvent all our current technological limits with faster-than-light breakthroughs, the question isn’t so much which is better but rather what are the next steps that we need to take to sort through all these crazy ideas? The point is to figure out the most reasonable next steps that we can actually afford and then have the best practitioners explore them and share the lessons.”
Does he think in his gut we’ll ever be able to reach across the light years to other solar systems? “I am certain that a dedicated interstellar probe will one day be launched,” he says. “I’m not sure when or by whom, but it is inevitable if humanity sustains some degree of vision about its future. But even if the desired breakthroughs turn out to be impossible, we will at least add to scientific and technical progress.
“What I am absolutely certain about is that we stand far more to gain in the attempt than to give up without trying. Discovering the means to allow humanity to live beyond Earth deals with our very survival and destiny as a species. It is not a trivial, discretionary issue. It would be socially irresponsible not to be asking such questions.”
For news about the foundation’s progress, visit www.centauri-dreams.org
For a further outline of the challenges involved in interstellar propulsion, visit www.nasa.gov/centers/glenn/research/warp/warp.html
by Paul Gilster | Feb 14, 2006 | Exoplanetary Science
Greg Laughlin’s systemic site, indispensable for those studying exoplanet detections, now offers a close look at Proxima Centauri, at 4.22 light years the closest known star to the Sun. Intriguing facts include these:
While holding about 11 percent of the Sun’s mass, Proxima has an average density several times that of lead (the Sun’s average density is about 1.4 times that of water)
Proxima’s total luminosity is a thousand times less than the Sun’s
Because radiation alone cannot get Proxima’s fusion energy from its interior to the surface, the star relies on convection — the motion of stellar gases physically takes energy away from the core (by contrast, the Sun has a radiative core)
All of which has powerful consequences, especially in terms of longevity — Proxima Centauri will still be shining two trillion years from now. You’ll want to read the entire post, which goes into the details of a paper Laughlin wrote (with Peter Bodenheimer and Fred Adams) that examines the fate of red dwarfs like Proxima. It also offers a close look at what a terrestrial planet orbiting a red dwarf might be like. And it reports on the work of UCSC graduate student Ryan Montgomery, who is carrying out computer work to simulate the accretion of terrestrial-mass planets from small planetesimals in this environment.
As for detecting such worlds, check this statement about using the transit method:
In principle, a 1% photometric dip is readily detectable, and in fact, amateur astronomers who participate in the transitsearch.org collaboration routinely achieve detection thresholds of considerably better than 1%… Skilled amateurs such as [Ron] Bissinger or Tony Vanmunster have backyard techniques that are good enough to detect the passage of even a Mars-sized body in front of an 11th magnitude 0.1 solar mass red dwarf. Wow.
Wow indeed. Laughlin lays out a list of candidate stars for potential transit detections and promises followups on Montgomery’s simulations. Oh, and the paper mentioned above is Laughlin, Bodenheimer and Adams, “The End of the Main Sequence,” in The Astrophysical Journal 482 (1997), pp. 420-434, abstract available here.
by Paul Gilster | Feb 13, 2006 | Breakthrough Propulsion |
In a paper to be delivered tomorrow at the Space Technology & Applications International Forum (STAIF) in Albuquerque, Franklin Felber of Starmark Inc. (San Diego) will present research on the gravitational field of a mass moving close to the speed of light. Without seeing Felber’s work, Centauri Dreams is reluctant to comment on his assertion in an article on the Physorg.com site that “…a mission to accelerate a massive payload to a ‘good fraction of light speed’ will be launched before the end of this century…”, other than to say that STAIF is a venue where fascinating ideas routinely emerge, not all of which stand up to scrutiny.
The paper is titled “Exact Relativistic ‘Antigravity’ Propulsion,” and it is followed by another intriguing title, “The Alcubierre Warp Drive in Higher Dimensional Spacetime,” by Eric Davis and H.G. White. Also worthy of attention is James Woodward’s “Mach’s Principle, Flux Capacitors, and Propulsion.” More on all three as information becomes available. You can find the entire STAIF schedule here.
by Paul Gilster | Feb 13, 2006 | Deep Sky Astronomy & Telescopes |
I wouldn’t dream of trying (nor would I be able) to explain string theory — for a popular treatment of that, see Brian Greene’s The Fabric of the Cosmos (Knopf, 2004). But I do know that ideas like string theory and supersymmetry arose to help us unify the world of quantum mechanics and that of general relativity. Extreme energies can unite electromagnetism and the weak force (think radioactive decay). The next generation of particle accelerators may unify both with the strong force (atomic nuclei bonding). But where will we get the energies needed to explore the unification of the quantum world with gravity?
The answer may come from outside the galaxy. Researchers at Northeastern University and the University of California, Irvine think that deep space neutrinos colliding with protons can release energies that test string theory. The notion is being examined in the AMANDA project, a neutrino detector at the South Pole. Although few high-energy neutrinos have been detected so far, the researchers believe a next-generation detector called IceCube, now being built, could help them compare ‘down’ neutrinos (coming in from above) and ‘up’ neutrinos (passing through the Earth and coming up from below).
“String theory and other possibilities can distort the relative numbers of ‘down’ and ‘up’ neutrinos,” said Jonathan Feng (UC-Irvine). “For example, extra dimensions may cause neutrinos to create microscopic black holes, which instantly evaporate and create spectacular showers of particles in the Earth’s atmosphere and in the Antarctic ice cap. This increases the number of ‘down’ neutrinos detected. At the same time, the creation of black holes causes ‘up’ neutrinos to be caught in the Earth’s crust, reducing the number of ‘up’ neutrinos. The relative ‘up’ and ‘down’ rates provide evidence for distortions in neutrino properties that are predicted by new theories.”
Centauri Dreams‘ take: Are we on the edge of the first experimental verification of at least some aspects of string theory? The potential seems clear, but using extragalactic sources as cosmic accelerators may reveal as many surprises as confirmations. What is germane to interstellar studies is that string theory posits extra dimensions via its exquisite mathematics, and promises to tell us much about the nature of expanding spacetime. But thus far even the most elegant of its predictions have proven untestable.
Is string theory a case of art masquerading as mathematics, what an old professor of mine used to call a ‘rabbit hole’ for the unwary, or a description of underlying physical realities? The sooner we start finding out, the better, as the amount of intellectual capital being expended on strings and the theories that bind them is breathtaking. The paper is Anchordoqui, Goldberg and Feng, “Particle Physics on Ice: Constraints on Neutrino Interactions Far above the Weak Scale,” in Physical Review Letters 96, 021101 (2006). An abstract is here.
