TerraFrost wrote:<snip>

as far as space ships being able to travel at or faster than the speed of light... i believe there was a scientific american article that talked about possible engine designs (although all of them depended on technologies / theories that hadn't yet been developed), but perhapes my memory fails me... i can't find any websites talking about such things, either...

I can't talk authoritatively about "faster than light" travel, btu I can talk about "close to the speed of light" travel.

One of the weird things that Einstein predicted was that the faster you travel, the slower time passes for you. I forget what the exact formula is, but it's not too complicated.

The example usually given involves twins. One stays on Earth, the other travels at something like 80% of the speed of light to someplace, then comes back. The twin who stayed on Earth will be older than the twin who traveled.

This effect is called "time dilation."

Another interesting thing is how fast you can go in space just by constantly accelerating. Our current space ships (rockets) only accelerate for a short period of time, a few minutes, then coast most of the way. They coast at thousands of miles per hour, but that's pretty slow in space.

If you can accelerate constantly for a long period of time, you can achieve enormous speeds. You don't have to accelerate hard to do this either; it can be a very gentle acceleration, just as long as it is constant.

An example of how this can shorten space travel involves travel to Mars. The way we do it now, we launch a rocket that burns for a short time, then the spaceship coasts around the sun eventually catching up with Mars. It's a journey that takes months.

I don't have the math right in front of me right now, but if I remember correctly, an acceleration of as little as 1/10 of a gee (or 0.98 meters per second per second) will get you to Mars in about 7 days. The same acceleration will get you to Pluto in 7 weeks.

To picture how little this acceleration is, a car accelerating from a stop at 1/10 gee would take 10 or 11 second to get to 30 mph. On the other hand, if the car could keep accelerating at that rate for an hour, it would be going almost 8000 mph. If the car kept that slow acceleration up for 24 hours, it would be going almost 190,000 mph. If it kept it up for a month, it would be going 5 or 6

million mph.

Anway, when I first read about this, I started wondering what that would mean in terms of making interstellar travel possible. I worked up a spreadsheet that let you enter an acceleration, and then it would tell you how long it would take to get to verious locations, like Alpha Centauri, the Andromeda Galaxy, across the universe, you know, the places everyone wants to go.

I quickly realized that unless I took relativity into account, my math was meaningless because it showed me exceeding the speed of light fairly quickly. So I found a formula that took time dilation into account and put it in my spreadsheet.

In a nutshell, what it showed was that if we could design a ship that could achieve a constant acceleration of one gee, meaning the passengers would feel the same force that we do on the surface of earth, humans could travel anywhere in the universe within a typical lifespan of 70 years. This is because the spaceship would be traveling so close to the speed of light that the passengers' time would slow down and they would still be alive at the end of the journey, even though thousands of years might have passed on Earth.

It's weird, and I don't think I did a good job of explaining it. It's a lot clearer if you just do the math.

The main thing is, interstellar space travel is in theory possible already. It's just up to the engineers now, to build a spaceship that will support humans for years, and to give it a propulsion unit that will accelerate it at one gee for years.

The only problem is that it would be one-way travel. You couldn't come back and tell anyone about it, because everyone left behind would be long dead. So true two-way travel would still require faster-than-light travel.

Somebody else will have to figure that one out. I can't.