Magus55

Thought we could have a civil discussion that doesn't involve religion just for fun.

Do you think humans will be able to travel outside our solar system? I say no unless we either find worm holes( as an alternative, develop a gravity generator that folds space like in the movie Event Horizon), or develop technology that enables humans to withstand astronomical speeds and G-Forces.

Jesse

Magus55:
or develop technology that enables humans to withstand astronomical speeds and G-Forces.

Speeds are not a problem, since you wouldn't feel anything no matter how fast you were going, as long as your velocity was constant. G-forces result from acceleration, not speed. If you accelerate at 1 G increasing your velocity by 32 feet per second per second, then you would feel normal earth gravitation throughout the acceleration. This page does the math (including relativistic effects) and shows that at a constant 1 G acceleration for the first half of the trip along with a constant 1 G deceleration for the second half (so you'll be able to stop at your destination), you could reach the nearest star in just 3.6 years of shipboard time, and the andromeda galaxy in 29 years:

http://www.mathrec.org/old/last/solutions.html

However, because of relativity observers on earth would see the journey to the nearest star take a bit longer, and the journey to the andromeda galaxy would seem to take millions of years from earth's perspective (in general the time seen on earth in years will be a little larger than the distance in light years, assuming the travellers are going at a sizeable fraction of lightspeed for most of the trip). This page gives the shipboard time vs. distance for other destinations, and gives the general formula for shipboard time taken to travel n light years using the "accelerate at 1 G for first half, decelerate at 1 G for the second half" method as 1.94 arccosh [n/1.94 + 1] years (though it also mentions that for distances greater than a billion light years or so, you need to take the expansion of the universe into account).

Realistically, though, constant 1-G acceleration for even a few years would almost certainly require too much energy to be feasible in the forseeable future. If we ever visit nearby stars, it's more likely that there'll be some initial acceleration and then the ship will "coast" for most of its journey.

Here's a page that does some calculations for matter/antimatter fuel and solar sails (using solar wind to push it along--see below for an alternative), and concludes that they're both pretty unrealistic by today's standards:

http://www.physics.uc.edu/~sitko/Spr...ce_travel.html

And here's an article on "The Feasibility of Interstellar Travel":

http://www.planetary.org/interstellar/forward.html

They seem to favor crafts with solar sails pushed by lasers or masers located in our own solar system. And they argue that although such a thing would require a lot of resources to build, changes in the economy due to things like self-reproducing robots may make these projects feasible in the near future:

Another, longer article on lightsails pushed by lasers or masers, analyzing the details of the power needed, the payload size, the cost, etc.:

http://www.qedcorp.com/pcr/pcr/starflt.html

And here's a page on the power requirements for a Daedalus-style fusion rocket:

http://www.islandone.org/APC/Interstellar/02.html

RoddyM

To have a civil discussion we need to know what you are thinking when you say "humans will be able to travel outside our solar system".

Is it for the sake of the humans that are embarking on the expedition that it be done? Or is it that humans left behind on earth be able to communicate with those that have embarked? Do the humans that were present when the travellers embarked have to be alive when the travellers exit the solar system or is it sufficient that just some humans be present to receive communication?

And what is the purpose of this? Does our solar system have an exit point that is is some meaningful way significant scientifically? Do they have to be able to return to earth? And if so do they have to be able to return to earth within the lifetimes of at least some of the people that were present at their departure?

Bialar Crais

Can't see why that shouldn'tbe possible...

Of course, if we (humanity I mean) survives long enough it's bound to happen sooner or later. In what waym, shape or form tho'... I dunno.

Someone already mentioned the "relativistic rocket", an acc. of 1G, Tau Ceti is within easy grasp, Proxima Centauri and Alpha Centauri is a mere stroll down the block (then of course, communicating back to earth, or returning may be a bit´difficult but reaching...).

Then there's generation ships. If a large enough ship can be buildt, with good enough recycling and whatnot to emulate an self-sustained eco-system it's an feasible option.

Oh, and I tag Barnards Sta5r for me and my descendants. Since I played Elite2 (even if I find the original Elite a lot more fun), I always wanted to own Barnards Star

Answerer

Let me guess. Magus55 is actually hoping for a 'Noah Ark' to be built.

RoddyM

Why, or how, "on earth" would a "relativistic rocket" have an acceleration of 1g. What is so special about 9.8 m/s2 that makes it special enough to be "relative"?

Jesse

You misunderstand, it's just called a "relativistic rocket" because after accelerating that way for a while it will be going a significant fraction of light speed. Any other acceleration will do, but 1 G would be most comfortable for human travellers.

Asha'man

The real limitation for interstellar travel is either energy or time. You either need to hibernate for the entire (very long) trip, or have a huge supply of energy so that constant acceleration can be applied. As was pointed out earlier, a constant acceleration around 1G is more than sufficient, even .1G makes for a reasonable trip.

To apply acceleration for extremely long periods of time, you need energy, and almost unlimited amounts of reaction mass. Fortunately, there may be a way to grab both from interstellar hydrogen. I recall that Larry Niven wrote about the Bussard ramjet, using a magnetic field to scoop up unterstellar hydrogen, compress it, and burn it in a fusion reaction, providing both energy and reaction mass. I think this type of technology might be feasable in the next 100 years or so.

Unfortunately, I don't think human civilization is going to last 100 years. I think we are going to tear ourselves apart with war and terrorism (probably over religious issues) and then finish the job with a simple disease like SARS.

Abacus

A 1g acceleration is often cited because it is about the maximum acceleration that would allow the ship to achieve relativitstic speeds quickly and still be comfortable for the crew. You wouldn't want to be on-board a ship accelerating at 2g or more for too long. After a year of accelerating at 1g, a ship would travelling nearly 80% the speed of light.

RoddyM

OK Jesse. Magus55 has asked us to comment on what we think is possibly possible, possibly even without sci-fi.

Sure, maybe he can't post back right now, but we need to know what he is really wanting or at least dreaming about.

Conventional rocketry using huge craft with a lot of stages and a lot of fuel could probably propel a living person, born before take-off, beyond the orbit of Pluto. It might be that the launch pad would be on Mars. It might be in 2080. It might be that a similar mission undertaken in 2095 from Earth would overtake the person launched on the first mission.