DescentBB

Ok, I have a question,

According to what I understand about relativity, as you speed up, time around you speeds up but your time slows down. This is if I remember correctly.

Now in the film Red Planet (and I have seen something like this in Mission To Mars), they only have a 45 minute time lag when sending a signal from Earth to Mars. (from what I understand this is true.) So why wouldn't the same thing happent to a signal like that? Why wouldn't it also arrive years after it is sent at that speed? Why isn't it effected by relativity in the same way that traveling at the speed of light would effect you? Anyway, just wondering. I'm going to start reading some Steven Hawking soon.

If the signol is sent at the speed of light, then it is a light signol.

Light is relativity, relativity came to be because light simply isn't relative. If I am running with a towards a flashlight I will measure the speed of light to be 3*10^8 m/s. If I suddenly stop running to take my measurement again, I will still measure it to be 3*10^8 m/s.

If it is not a light signol then it would be traveling much slower then the speed of light, and not be affected by relativity.

Or, you can take my approach and think that relativity is mostly b.s., but then you have to accept quantum physics, which I would also like to think is b.s.

But unfortionately one of them is probably true.

That be "signal" Goob.

woodchip wrote:That be "signal" Goob.

Or signog if you're Duper.

You do remember correctly. It's all about frame of reference. Say a person leaves earth on a spaceship to tour the solar system at 0.5c today and returns on Christmas. When she returns, we'll have been waiting 21 days for her homecoming, but her shipboard clock will say that she'd been gone for less than 21 days. I have no idea how much time dilation you get at 0.5c, but let's say she's only aged 17 days. If she'd gone faster, say 0.9c, she would have aged even less, maybe a mere 5 days. This is the primary appeal for commercial space travel: so rich kids won't have to wait as long between Santa visits.

In your movie example, the 45 minutes is how long those of us in the external frame of reference have to wait for the signal to traverse the distance. The external frame of reference includes Earth and Mars. However, if you could imagine that a mini-you was surfing a photon in the signal, you'd be in the internal frame of reference, much like that woman on the spaceship in December. You would indeed experience time dilation just like she did, and the trip would take a helluva lot less than 45 minutes from your point of view.

Unfortunately relativity is a bit funkier for your example than it is for the woman in the ship. As Goob pointed out, radio signals travel at light speed. The problem is that the time dilation effect becomes more and more pronounced the faster a spaceship goes (remember the woman aged less at 0.9c than 0.5c). So what happens when you hit 1.0c? The time dilation would become infinite, meaning time would stop onboard the ship. This seems impossible, and so we have the layman's version of why we believe physical objects cannot be accelerated to light speed.

So of course you couldn't surf a photon on the radio signal, not just because you can't surf well in a spacesuit, but because the photon isn't a physical object. But if a photon were self-aware and had a wristwatch, when it got to Mars it would say "you guys were waiting 45 minutes for me to get here from Earth? I just did the trip in 0.0 seconds!"

By the way, we've seen time dilation effects caused by relativity in simple experiments. Scientists took a pair of super-accurate clocks and put one on a satellite and left the other on earth. The one on the satellite ran just the teensiest bit slower than the one on earth. By exactly the amount predicted by the theory of relativity.

Excellent Ghenghis You just gave the special relativity in a nutshell.

A few precisions: the "speed of light" or the c constant is actually defined by the fastest possible interaction between two events in space, and one of the Einstein postulates says that this speed is finite (Newtonian gravity expects this speed to be infinite, meaning two events in different locations interact instantly). This speed happens to be the speed of photons in vaccuum (photons slow down in a medium, say air or water).

The reason photons travel at the speed of light is because their rest mass is zero. Photons can be regarded as particles with the duality-theory. Depends how you want to approach a problem.

The general relativity theory (not the special one Genghis explained) is a lot more complicated, I'm studying it now at univ

I was thinking about trying to use the little knowledge of relativity that I have to try to calculate the discharge mass and time it would take to realistically get to alpha centari. I've got a question regarding that- Say, you're going .5c in the positive x direction, relative to you're destination. You're also trying to accelerate by spewing mass at a certain rate at .95c relative to the ship's frame. (assume you've got heck of a good engine)- So, I want to use the Newtonian momentum theory to find out how much faster the ship is going after spitting one one dmass. I have to correct for the whole relativity thing, so do I do so by correcting both masses, or by correcting the emission speed to be relative to the fixed frame? (Or a combination of the two?) If both work, it's all about the speed correction because that's an easy subtraction, but I'm thinking that the mass correction would be more correct.

(Now that I think about it, actually the mass correction would be alot better- because when the ship starts at a stand still, the emission mass will actually accelerate the ship more than Newton's theory would predict because of the gaining of effective mass, eh?- Essentially if one could develop en engine that could emit particles at nearly the speed of light, it would be able to produces gobs and gobs of acceleration with next to no mass.)

You guys realize what this means? If you could get going fast enough, you could invest say $1000 in a bank account at a good interest rate, hop in fast ship, fly around at very high rate of speed for a while, come back, and your money would have greatly increased in value...

Interesting, I'm probably going to have to read a bit into this. You guys explained it a little better. Hopefully I will be taking some physics courses next year after I move out.


So in other words, if you were to travel light speed, you would arrive at Mar's in 45 minutes just as the signal would. This makes more sense to me. I didn't know that the signal would travel at light speed so this is what threw me off. Boy was I off. I am a physics newbie, heh.

Ok, just wondering, say if you could somehow board this light and you flew on it for one lightyear, how would your time appear? To you, would it only be a few minutes or even days rather than a year?

mob-messenger wrote:So in other words, if you were to travel light speed, you would arrive at Mar's in 45 minutes just as the signal would. This makes more sense to me.

Correct me if I'm wrong, but according to Geng's explanation, the trip would seem to be instantaneous, even though to the observer on Mars it would take 45 minutes.

here you go, http://www.johnstonsarchive.net/relativ ... alrel.html
a little light (haha small joke there) reading cos i,am too lazy to right any of it down.

ps. a little fun trick to prove to the kids that electricity is faster an soundwaves get to get two tv`s tuned to the same channel in separate rooms, place one telephone to one speaker and in the other room with the other tv listen to the phone and you,ll hear the other rooms tv a faction of a second before the one in the room with you, keeps the kids amused for a while

That happens in my house when you stand on the stairs, you can hear the time gap between the downstairs and upstairs TV's

In fact relatativistic effects can be measured between the distance at the top and bottom of skyscrapers: the top experiences time slower than the bottom due to the increased speed because it juts out from the surface of the earth. It's a rock solid phenomena.

And yes, a Photon won't "experience" any time during its travels.

Time dilation, as far as humans are concerned really doesn't become much of a factor until you get to about 95% of C - and it's at the same point where Mass starts to increase dramatically - so it's very very very hard to accelerate once you reach those speeds.

I believe Einstein was right about Light Speed being unobtainable, but I believe it may be possible to travel somewhere faster than C by folding the universe such that distances between points are effectively zero - thus effectively bypassing the problem.

Does Einstein's work not take the curvature of the universe into account? That folding shortcut would only work if Einstein only saw a uniform universe, right?