Sake:
Sorry about the name misspelling.
JonF: 26-100
Scylla: No doubt we earth-dwellers would have further developed these technologies long ago if there were a brass ring closer than 4.3 light years away.
How close could star systems be and still alow for the possibility of an earth like world or a least stable planets?
He does spend a chapter on the possibility that there IS a star much closer.
We have only catalogued the 300,000 brightest stars in the sky, using parralax to determine their distance.
It’s possible that there might be a dim uncatalogued star as close as half a light year.
There is some “evidence” that there is a large stellar mass close to our solar system, based mostly on the periodicity of large meteor showers, and cometary action.
The idea is that this stellar mass disturbs the Oort cloud and sends comets and such flying towards the inner part of the solar system when it passes close by.
There is even a name for this star “Nemesis.”
The chances of this actually being the case are quite low.
I guess we just have to envy those civilizations close to the Galactic core.
Often wrong… NEVER in doubt
Scylla - no problem, everyone misspells my name. Thanks for the info on the sails - that’s some serious power usage! I just love the image of a cosmic sailboat. Space Pirates!
I have also heard some theories that our system is a binary one. Any evidence to this?
Hell is Other People.
Sake:
Yes, as in previous post, the hypothesized dim star is called “NEmesis”
Often wrong… NEVER in doubt
What other evidence besides “the periodicity of large meteor showers, and cometary action”?
At what distance does our sun’s gravity become negligable?
The possibility of a dark companion to our sun was first postulated in the SF novel Lucifer’s Hammer by Larry Niven and Dr. Jerry Pournelle, back in 1979, IIRC.
When Walter & Luis Alvarez announced their theory that a comet or asteroid collision had exterminated the dinosaurs, Walter said, “Lucifer’s Hammer killed the dinosaurs.”
A few years later, some astronomer (Damn me for forgetting his name) postulated the Nemesis theory. I wrote a fan letter to Larry Niven to inform him and he was grateful, for he had not known that an active search for Nemesis was underway. (Wish I still had that letter. sigh) And it was Mr. Niven who related the Alvarez story to me.
Nemesis has yet to be found. However, that theory led to the theory that some of the so-called “dark matter” of the universe may be “brown dwarfs” like the putative Nemesis.
The thing is, it seems to me that even if Nememsis does exist, it would not be worth it to send a manned mission there, unless it were to be used to provide a boost in speed and/or fuel. Send a Galileo-type probe, sure, but the other stars with their possible worlds and possible life deserve to be observed directly.
Final thought: Read Arthur C. Clarke’s last Odyssey novel? There, he describes the inertia-less drive, which he, in turn, based upon theories created by qualified physicists. (Discover magazine once had an article about this.) To wit: Inertia may actually be a force like gravity or magnetism that works opposite to any change in direction or velocity. If so, could it be weakened or even eliminated, thus giving a spacecraft less mass and less inertia and thus be more easily accelerated? We have not been able to do this with gravity, of course, but who knows? Maybe inertia works so much differently from gravity that it’s actually easier to oppose, if we only knew how.
>< DARWIN >
__L___L
The meteor shower refers to the Dinosaur killer asteroid and other such events which seem to occur pretty regularly every 26 million years or so. The “Nemesis Star” travelling in a slow orbit about our sun with Aphelion of 2.78 light years, and Perihelion of .01, would disrupt the Oort cloud sending large cometary masses into the inner solar system, thus accounting for the repeated mass extinctions (this is pretty much me paraphrasing Zubrin.)
Other evidence is the “mass problem” of the galaxy and universe. According to the observable mass of the galaxy it should not rotate or orbit the way it does. It needs a lot more mass to do so.
There might be a lot of dim or unignited stars out there (among other things), making up this mass.
He says there are literally billions of potential candidates for Nemesis each of which would have to be examined.
He says “Without passing judgement on the veracity of any of these theories, it is sufficient to observe that there is a significant body of evidence that currently undetected objects of stellar mass may exist in our near stellar space.”
As to where gravity from the sun is no longer significant, I have no idea. I think it’s an inverse geometric progression, and drops off pretty quick (in terms of stellar distances,) but that’s just a guess.
Often wrong… NEVER in doubt
Fogmage:
Re: your question:
I guess pretty close. Jupiter is about 1/100 of a solar mass and produces heat by compression. It has stable satellites, but you don’t have to be too large to accomplish that. I don’t know if Jupiter’s satellites are large enough to have ever had the possibility of being earthlike.
The theorized Nemesis star could easily have planets worth making the trip, if it exists.
Most of this thread has been about a MANNED mission to Alpha Centauri. How about the feasability of an unmanned probe? Since it would be smaller & need less shielding, could it not travel faster? Would it be possible to send the probe and hear from it in a reasonable time frame, say 10 - 15 years? 
“If we would have new knowledge,
we must get a world of new questions”
Alright, I tried to be helpful and include a link to the nifty new GD thread where this discussion can move to, and the joyous flood protection decided that the original of this post was not acceptable. I wouldn’t have a problem with this, except that it DELETED MY NICE LONG REPLY. Anyway, I’ve decided to move the thread about practical interstellar travel to the thread below and I’m going to reply to specific points tomorrow. http://www.straightdope.com/ubb/Forum7/HTML/001094.html
Kevin Allegood,
“At least one could get something through Trotsky’s skull.”
- Joseph Michael Bay
The “inertialess drive” goes back at least to E. E. “Doc” Smith’s tales of the Lensmen.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
What follows is what I came up with while I was reading the previous two threads. Some of it is a repeat of what has already been said, but I thought of it before I read it so it counts.
Boris B:
This was actually a big arguement during the formulation of our current rocket technology, but a simple application of the fundamental laws of physics will suffice. For every reaction there is an equal and opposite reaction. Therefore, the space shuttle moves at constant acceleration and increasing velocity all the way out of the atmosphere and in space. Think of it like this, as the space shuttle moves forward its motive force, fuel and engines, moves in step - it does not move relative to the space shuttle and nothing has changed from that perspective. Who’s confused?
Riboflavin:
I believe we are roughly on the same page with that whole calculation thing except where you refer to a return trip. That just won’t be done.
Atrael:
No, it’s not looking good for fission/fusion technologies to take us anywhere.
Fission/fusion would be a far better answer that our current liquid/solid fuel thrust technologies due to the available energy density. I’ve not been to Astronomics 8.01, but the fission/fusion (which incidentally release about the same amount of energy as far as I know - it’s all E = m c^2 stuff) of a couple atoms of hydrogen yields astronomically much more energy per gram than that produced by the burning of hydrogen. However, whatever is finally used will undoubtedly include at least a couple of sling-shots around the sun.
Scylla: At what distance are binary stars called binary stars? Wouldn’t a binary star have to be much closer to the Sun to be called that? I’ve really got no idea.
Jab1:
What do you mean may be? I AM a cosmic force.
There are several technologies which have been developed or are under earnest research that will contribute greatly to humankind’s exploration of the universe. Firstly off the top of my head is the idea of negative energy. I’m not even going to pretend I understand it (and I know a lot of stuff, just read the steak thread), but you can read all about it in the January 00 issue of Scientific American. In summary it describes how it is possible to created artificial worm holes and/or “warp” technology. Unfortunately, with what they (certainly not me) understand about it, these phenomena would require more energy than is contained in all of the universe. Oh well, at least they’re working on it. Previously Scientific American, in one of their quarterly dedicated issues, focused quite a bit of discussion on space technology. From this we learn that there is some guy who attempting to build a 1-mile wide sail out of ionized plasma. In some such way, this sail will be able to take advantage of the solar wind, the stream of our sun’s ejecta. This sail has many benefits over the traditional idea of sail namely much less mass and it will be immune to holes made by space dust. Thirdly, noone is discussing the use of a-bombs any more. The discussion has moved on to the the use of actual, living, breathing anti-matter. Further: On the Discovery Channel we learn that a realistic expectation of reaching Alpha Centauri is something along the line of 100 years. 100 years for the passengers and longer for their relatives/descendants left on the Earth. I don’t know what the conversion would be, but I know that they’ve already tested the phenomena of time distortion by flying an atomic clock around the world on a jet (not very fast relatively/relativisticly speaking). When the clock was returned to the starting point it was compared to its sister clock and found to be off. For a watch that is supposed to lose one second every million years (something like that) any difference is significant.
My thoughts on extraterrestrial life: Yes, there is life outside of our solar system. Does it look like us? Superficially no, but it’s body chemistry will undoubtedly be based on the properties of either water at temperatures we are used to or based on liquid methane a few degrees kelvin.
Has anyone read the Rama series by Arthur C. Clark?
I keep hoping the guys at CERN are going to develop anti-grav technology. It’d be a cinch to get anywhere after that.
To further the conversation, what does anyone know about the X-33 or X-34 projects? It currently costs $20,000 to launch 1 kilogram into geostationary orbit. The X-3x programs promise to bring that figure down to $2,000 in the VERY near future and maybe within’ 5 years. Matter of fact, there’s a company that is already selling tickets for space rides. Who would move to the Moon or Mars if given the opportunity? Once it is less cost-prohibitive to actually launch equipment into space the whole industry of asteroid mining is poised to actually MAKE MONEY IN SPACE. Then, of course, there’s these guys at P.E.R.M.A.N.E.N.T.
Snap into a slim jim!!!