[Livingston]

Originally Posted by Zardoz

So if you had to get from here to Alpha Centauri and retrun within...let's say 10 years earth time, how owuld you do it?

I'm not sure what percentage of the speed of light you would have to travel to get there 10 years earth time. If you went at near the speed of light and say it took you 4 and half years to get there cause I think it's 4.5 light years away, I'm not sure how much time would pass on earth. Quite a bit more, but not sure how to calculate that. A round trip to alpha centauri at near light speed would be almost ten years for you, don't know how many it would be for everyone else.

[MrQ1701]

Originally Posted by Livingston

I'm not sure what percentage of the speed of light you would have to travel to get there 10 years earth time. If you went at near the speed of light and say it took you 4 and half years to get there cause I think it's 4.5 light years away, I'm not sure how much time would pass on earth. Quite a bit more, but not sure how to calculate that. A round trip to alpha centauri at near light speed would be almost ten years for you, don't know how many it would be for everyone else.

I always understood the theory of relativity would make that kind of trip to Alpha Centauri and back, within ten earth years impossible. If the ship travels at near light speed it would take at least 9 years for the round trip, according to time on the ship. So time on earth would have passed at a greater rate...say 20 years. Or do I have that whole thing backwards and time on the object moving at near light speed actually is accelerated?

[DNA-1842]

A Lightyear is the distance that light travels in one year - from the outside (I think).

[Zardoz]

Originally Posted by MrQ1701

I always understood the theory of relativity would make that kind of trip to Alpha Centauri and back, within ten earth years impossible. If the ship travels at near light speed it would take at least 9 years for the round trip, according to time on the ship. So time on earth would have passed at a greater rate...say 20 years. Or do I have that whole thing backwards and time on the object moving at near light speed actually is accelerated?

So you don't come home to "Planet Of The Apes?"LOL

11 year gap isn't too bad.

[Elizadolots]

MrQ wrote:

So is light just energy, or a particle? I thought a photon was a light particle. I thought particles had mass. I think the lines between matter and energy aren't as concrete as some believe. I also saw on TV (the universe) that tachyons are theoretical particles that DO travel faster than light.

Which nicely summarizes the problems….is light energy? Yes, but it also behaves as if it is made of particles and particles have mass. What theory you are trying to support determines which image of light you will adopt….not exactly the most consistent concept, is it?

According to NASA, tachyons have mostly been abandoned as a practical theory.

http://www.nasa.gov/centers/glenn/re...p/warpfaq.html

So far any attempt to observe a tachyon has come up dry, and most physicists have abandoned the idea that tachyons might be real.

Livingstone wrote:

Anyone know anything about wave duality, everytime I read something on it it's difficult to grasp fully, Shrodinger's Cat and all that, it's a very strange concept, but seems to be very much grounded in fact from what I've read.

well…I think the wave duality thing is related to the basic conflict in light theory, but I could be wrong….I’m calling PETA! Shrodinger’s had that cat locked in a box for a really long time!

And:

In Dune they fold space, they actually take two points in space and fold them on top of one another so the points occupy the same place and time and then the trip is instantaneous.

That was actually proposed earlier in a “young reader’s book” and called a teseract. It was “A Wrinkle In Time” written by Madeline L’Engle in 1960. I guess it’s likely that others have offered up that concept before as well because it’s a nice, easy to visual idea.

As I understand it, both MrQ and Livingstone are right on the way time would be distorted by traveling faster or as fast as the speed of light: to the traveler less time will have passed than to those left behind.

[FanWriter45]

The thing is about time dilation: it's an ever increasing curve. Up until about half light speed, you really don't notice the effect of time being different to the crew as it is to folks back home. At about 3/4 lightspeed, the elapsed time seems to be cut about in half. But, as you get closer and closer to lightspeed, then you start making some real headway...

Just supposing you could get a ship to within 99.9% the speed of light almost instantly, The trip to and from Alpha Centurai would seem to take only a few days. But, no matter how fast you travel, time continues to move at the same rate it always has back home... So to folks on Earth, your ship still takes 4. 3 years each way.

Theoreticaly, if you could accelerate to 99.99999999999% of c, you could cicumnavigate the known universe within a human lifespan. However, by the time you got back home, the sun will have long since burnt out.

You might try reading the novel "Tau Zero" by Paul Anderson. In it, a ship does almost exactly that. Thanks to some damage passing through a dust coud, a Bussard ramjet finds it can't stop accellerating...

[FanWriter45]

Oh, yeah, and Gerry Anderson did a TV special with Nick Tate and Brian Blessed, called "Into Infinity" about a family travelling to the nearest star in a reletavistic, photon drive ship called the "Alteres." It's a great little primer on what some of the effects of near-lightspeed are.

Time dilation
Mass increase
foreshortening of dimentions in the direction of travel
Doppler shift

[MrQ1701]

Originally Posted by FanWriter45

The thing is about time dilation: it's an ever increasing curve. Up until about half light speed, you really don't notice the effect of time being different to the crew as it is to folks back home. At about 3/4 lightspeed, the elapsed time seems to be cut about in half. But, as you get closer and closer to lightspeed, then you start making some real headway...

Just supposing you could get a ship to within 99.9% the speed of light almost instantly, The trip to and from Alpha Centurai would seem to take only a few days. But, no matter how fast you travel, time continues to move at the same rate it always has back home... So to folks on Earth, your ship still takes 4. 3 years each way.

Theoreticaly, if you could accelerate to 99.99999999999% of c, you could cicumnavigate the known universe within a human lifespan. However, by the time you got back home, the sun will have long since burnt out.

You might try reading the novel "Tau Zero" by Paul Anderson. In it, a ship does almost exactly that. Thanks to some damage passing through a dust coud, a Bussard ramjet finds it can't stop accellerating...

Now I am all confused!!. I don't see how this can be true. I thought the crew on the ship would experience a 4.5 year (or 4.3?) trip if, somehow, they traveled at light speed. I mean, that is how a lightyear is defined right? Now, after another 4.5 year trip back home the crew would find time on Earth has passed at a greater rate (I have no idea the math involved here) say 20 or maybe 100 years.

So if my thoughts are correct, then traveling at light speed a person could only travel...say...100 light years if he/she lived that long.

[Livingston]

Originally Posted by MrQ1701

I always understood the theory of relativity would make that kind of trip to Alpha Centauri and back, within ten earth years impossible. If the ship travels at near light speed it would take at least 9 years for the round trip, according to time on the ship. So time on earth would have passed at a greater rate...say 20 years. Or do I have that whole thing backwards and time on the object moving at near light speed actually is accelerated?

Okay, scratch what I said, fan is right, I had it backwards!

If you're in a ship traveling to alpha centauri it'd take you four and half years to get there, that's how much time passes for people on earth. It takes light 4 and a half years to get from alpha centauri to here. The person on the ship traveling at near the speed of light, much less time will have passed cause from our point of view, time is traveling at a slower rate for the space ship traveling to alpha centauri.

If you travel to a star a thousand light years away, a thousand years will pass for everyone else in the universe, whereas perhaps hundreds or less would pass for you on the starship, traveling near the speed of light. I'm not sure how to calculate the degree of time dilation but what fan is saying is right. From the outside, looking in, our perspective, it'll take a ship ten years to get to a star ten light years away, whereas only a fraction of that time will have passed for our passengers on the space ship.

[Zardoz]

Originally Posted by Livingston

Okay, scratch what I said, fan is right, I had it backwards!

If you're in a ship traveling to alpha centauri it'd take you four and half years to get there, that's how much time passes for people on earth. It takes light 4 and a half years to get from alpha centauri to here. The person on the ship traveling at near the speed of light, much less time will have passed cause from our point of view, time is traveling at a slower rate for the space ship traveling to alpha centauri.

But what kind of traveler to earth time ratio are we talking?