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Alien Solar System Much Like Ours
MrGort writes "Wired News reports that British astronomers say they found the first sun-like star with a giant gas planet in an orbit similar to Jupiter's, which leaves plenty of room for worlds like Earth and Mars. This system is a quick 90 light years away. The similar solar system to ours means that this gas giant could attract most of the debris, allowing smaller planets closer to the sun to develop like ours did!"
Hate to be pedantic, but using the proper terms aids clarity and, of course, helps one to sound credible, so let me offer this helpful advice:
There is only one "Solar System," and that's the system of bodies orbiting our star, Sol.
The generic term for any other collection of planetary bodies orbiting some random other star is "planetary system." The planets therein are referred to as "extrasolar."
Read the original press release and paper. You will see this usage reflected there.
Re. slower than light travel - if you get fast enough (i.e. a sizable fraction of c), then, even if it takes dacedes to get where you're going, time dilation will mean that far less time passes for the crew of a spacecraft - so, if you're going fast enough, a trip of 90 light-years, say, could be accomplished within the natural lifetime of the crew without FTL travel.
evil math within Nature's Cubic Creation!
I agree with you that we shouldn't be too pessimistic, however the Wright Brothers' flight was more of an engineering challenge than a scientific one. They required no novel physics to accomplish their feat, only the application of known physical laws. It will be possible for us to explore our own solar system using known physics by using nuclear propulsion (fission and some day fusion) and even solar sails. However, travel to other stars in less than a human life-time in our frame of reference will require super-luminal speeds. There is no physics known yet that will allow us to achieve this. So, interstellar travel will be a lot harder for us to achieve than the Wright Brothers' first powered flight.
Stick Men
(a) Most physicists think gravity is transmitted at light speed. Very few (and none who believe in General Relativity) think gravity is instantaneous.
(b) (I Am A materials scientist) "Solid" matter is composed of atoms bound together by electromagnetism. When you "push" a solid object, displacement waves (essentially sound waves), travelling from atom to atom inform the material that you are pushing it. For sufficiently fast pushes and short timescales, even a block of carbon steel looks like a wobbly jelly. This is important in impact engineering, for example, and mechanical engineers and materials scientists deal with stress waves in solids all the time (plastic torsion waves are the most "fun"). Nothing is perfectly solid.
Your "stick to europa" would have to have unphysical infinite rigidity for instantaneous transmission. In real life, assuming you could make a stick to europa (not in itself unphysical, just extremely unlikely), a wave train would travel down the stick when you displaced one end, displacing the material of the stick. This would happen at the speed of sound in the stick, which is always significantly lower than light speed (since it is determined by interatomic interactions, themselves subject to light speed) So yes, conceivably, the drum would make a sound, but the sound would come some time after you pushed the other end of the stick, since the stick would be acting like a wobbly jelly on such a scale, as all atomic matter must.
You can even see this in action - surely you've seen the high-speed movies of bullets hitting apples, with deformation waves crisscrossing the surface? All solids behave that way, it's just the waves travel very quickly (but not nearly as fast as light...) in some solids such as hardened metals.
True, there may eventually be laws that allow for faster than light travel (wormhole anyone?) But the Wright borthers had birds as examples that flight was possible. We don't have any physical evidence of super-luminal travel being possible.
Re. slower than light travel - if you get fast enough (i.e. a sizable fraction of c), then, even if it takes dacedes to get where you're going, time dilation will mean that far less time passes for the crew of a spacecraft - so, if you're going fast enough, a trip of 90 light-years, say, could be accomplished within the natural lifetime of the crew without FTL travel.
There turn out to be practical problems with this. Any craft that carries its own fuel with it - including the more practical breeds of antimatter drive - will be limited to a crusing speed of about 0.1-0.2C by the specific impulse of their fuel. The only thing that could approach speeds at which time dilation would be significant is a beamed core antimatter drive (that uses the charged particle shower from an antiproton annihilation as the reaction mass), but that requires unrealistic amounts of antimatter (positrons are easy to make, but antiproton synthesis is very inefficient, and will remain so unless new physics is discovered).
In principle, some kind of sailcraft driven by a stationary laser or maser array could reach relativistic speeds, but the array would be very expensive to build and very large (we need to focus on a planet-sized sail at a range of many light-years). It would also work wonderfully as a weapon capable of melting cities to slag at a range of hundreds of AU (or even light-years, depending on configuration), so I suspect non-proliferation agreements would prevent it from being built in the first place.
In short, the only hope for relativistic travel at less than colossal cost is new physics.
It's been far too long since I read a non-fiction book with spaceships in it, but can't you (in theory) propel a spaceship by shining a very powerful light out of the back, using the photons themselves as the reaction mass? Then could you get nearer to c?
You can, but the problem is generating the light in the first place, and the fact that light has a lousy ratio of momentum to energy (it has to be very, very bright to generate significant thrust).
Most light sources that are bright enough to move a ship at any reasonable acceleration (e.g. fusion bombs wrapped in other matter or just shining on a shield block that can tolerate gamma rays) waste matter - the energy to mass ratio of a fusion bomb is much worse than that of the photons you're driving the ship with. This means you'd be better off just using a magnetic bottle to deflect the plasma resulting from the fusion explosion, and you'd still end up with specific impulse too low for relativistic flight.
A light source that doesn't ablate or otherwise lose mass has to be relatively dim (either a hot block of solid matter or a confined plasma ball), which means getting anywhere will take an extremely long time.
The forms of light propulsion that I've seen considered involve generating the light somewhere else (e.g. a laser array) and just reflecting it off the craft's sail. You still have a drive that's horribly inefficient energy-wise, but the energy source doesn't have to travel with the craft.
For reference, power to thrust is 3e8 W/N for a photon drive (energy to momentum ratio is C for photons).
I think they're hoping to detect a transmission that is meant to be detected, in the range 1.4--1.7 GHz. In that range, the thermal background of the sun is about 1e10 watt, so only a very directional narrow-band transmission has a chance to be noticed.
I remember that people have tried to send a message to a few nearby stars a few years ago with a powerful directional transmitter. The message was a series of pictures, explaining how we look like, how we count, what our solar system looks like, etc. I can't remember what it was called, but that's the kind of transmission that we might receive.
Avantslash: low-bandwidth mobile slashdot.
A bit more info from a previously submitted post:
New Jupiter-like Planet Discovered in Sol-like system
A new Jupiter-like planet has been discovered in a circular orbit around a Sun-like star 90 light-years away in the constellation Pupis. What is remarkable about the discovery is that this system is the most like our own solar system discovered to-date. This development lends credence to the theory that systems with small, rocky Earth-like planets are out there. ''This is the closest we have yet got to a real Solar System-like planet and advances our search for systems that are even more like our own,'' said UK team leader Hugh Jones of Liverpool John Moores University. Jones went on to say that, ''Jupiter's position is probably crucial to the distribution of other planets in the Solar System.'' Current thinking on planet-formation indicates a large, Jupiter-like planet in a circular orbit would allow the relatively undisturbed formation of an inner system of smaller Earth-like planets. The newly discovered planet is about twice the mass of Jupiter with an orbit equivalent to the asteroid belt in our own solar system.
That's, of course, not the only kind of craft: ramscoop ideas have been around for a while, and while they're not exactly "production quality" ideas, there's nothing fundamentally killing them. We'd just have to figure out how to do fusion much better than we do now - which is not exactly new physics - it's new engineering.
Ramscoops are fundamentally killed by drag.
Consider a ramscoop to be a special case of a magnetic bottle. In a conventional magnetic bottle, matter leaks through "loss cones" at the pinch points of the mirrors. The tighter the constriction (i.e., the greater the field increase compared to the field in the middle of the bottle), the narrower the loss cone and the less material leaks out.
A ramscoop, on the other hand, works by passing material through the pinch point, hopefully with enough compression to fuse in the process. The problem is that, given the fact that the field is much larger than the coils used to generate it, the pinch point is very narrow indeed, and very little material gets through the loss cone (most is just deflected). So, you get lots of deflection and very little fusion to provide thrust. Bye bye dreams of ramjets.
Making the throat of the ramjet wider means less compression, and lack of fusion.
Using an active compression scheme (pulsed conical field coil, for instance) requires coils the size of the field - either heavy enough to make the ramscoop useless, or small enough to capture almost no fuel.
In summary, ramjets in practice don't seem to work very well.
Any relativistic craft launched would be sailcraft or other beam-driven craft of some kind, as that's the only way to provide enough energy to the craft.
Relativistic travel = huge cost (in 2003 dollars! note that economies of scale and necessity can help here. Automated antiproton factories, etc.: thank god for that tremendously huge fusion generator sitting next door pumping ungodly amounts of energy out all around us.)
Neither solar collectors nor antiproton factories are free, which means that the cost will always be significant. In practice, it will be colossally expensive to produce antiprotons for the forseeable future, for reasons outlined in detail in another post.
A phase-locked maser array would probably be the cheapest method for driving a relativistic craft, but has political problems outlined in my previous message.
A study was recently done where the speed of light was actually reduced. I am not sure the degree to which this was done, but the mear fact that this can be accomplished is something to raise at least an eyebrow over.
The propagation speed of light in a medium has been reduced in the lab - not the speed of light in vacuum, which is the important number.
There are hints that the speed of light has varied slowly over the age of the universe, but this doesn't help us build space drives.