PDA

View Full Version : Traveling at near the speed of light (questions for smart people)

OutKlast
08-20-2010, 12:43 PM
I was watching the TV series about the Universe and in the program they were covering the idea of relativity. More specifically they were talking about traveling at near the speed of light as a "forward time machine." The ratio mentioned was roughly 1:71.428 when comparing traveling at 99.9% the speed of light and someone on earth. So 1 unit of time experienced on this ship traveling 99.9% the speed of light is 71.428 units of time on earth. I understand this concept.

Here is my question, what would happen when you attempt to communicate between the object moving 99.9% the speed of light and the earth? Modern communications can essentially operate at the speed of light or very near to it.

See the following diagram (not to scale):

http://www.outklast.com/misc/errphyall.gif

The red dot is our spaceship orbiting the earth, at a distance, traveling 99.9% the speed of light. The green dot is earth. Around earth orbits outward facing satellites beaming communication (video/text/images/etc) outward in all directions simultaneously at light speed. The blue line is just an illustration to represent two way communications (from earth to spaceship / from spaceship to earth) which would travel at the speed of light.
How would this information arrive and be perceived?

Given the relative experience of time 1 day in the spaceship would cover 71.428 earth days. Would the spaceship get overloaded with information like watching a movie in fast forward? Would earth get a slowed down collection of information? I also understand the distance between earth and the spaceship (and thus the speed of communication) will play a role. Blow my mind, I'm ready.

Goose102
08-20-2010, 01:00 PM

My_Friend
08-20-2010, 01:10 PM
You basically answered your own question. Time slows down when you travel very fast so yes all communications from Earth would sound like a movie on fast forward and your own speech would sound very slow and low pitched to a receiver on Earth. You'd also have to adjust your receiver because the radio frequency would also appear to be much higher.

This is only if you travel in a circle. If you travel towards Earth, the pitch/speed will increase even more. I think another factor of 1000 on top of the time dilation.

My_Friend
08-20-2010, 01:15 PM
BTW according to wolframalpha the time slows down by a factor of 23.37 at 99.9% of the speed of light.

http://www.wolframalpha.com/input/?i=time+dilation+.999c

F.Liu
08-20-2010, 01:17 PM
Given the relative experience of time 1 day in the spaceship would cover 71.428 earth days. Would the spaceship get overloaded with information like watching a movie in fast forward? Would earth get a slowed down collection of information? I also understand the distance between earth and the spaceship (and thus the speed of communication) will play a role. Blow my mind, I'm ready.

You got it backwards, the earth would be overloaded with the information if anything, if communication were to happen (e.g. I transfer 1mb of information to the spaceship from earth in one day, it takes 71 days to receive it (easy transfer). The spaceship transfers 1mb of information to earth in 1 spaceship minute = 1/70 minutes on earth).

Assuming that the spaceship could 'see' the events happening on earth, it would be in slow motion, specifically 71.4 times slower (or whatever the factor is), and opposite for the observers on earth at 71.4 times faster (essentially the same thing with the 1mb of data example). The only way I could think of doing that is video cameras on the spaceship and earth for observation. Moving at 99.9% the speed of light may screw up the EMR signals though, idunnolol.

Plus the diagram is pretty inaccurate, as maintaining a stable orbit around, say, a solar system at 99.9% the speed of light would require probably light years in radius. So really, there isn't a physically possible way to experiment, and what I said above was theoretical.

Orbiting around black holes may also interest you, OP.

My_Friend
08-20-2010, 01:21 PM
Plus the diagram is pretty inaccurate, as maintaining a stable orbit around, say, a solar system at 99.9% the speed of light would require probably light years in radius. So really, there isn't a physically possible way to experiment, and what I said above was theoretical.

Orbiting around black holes may also interest you, OP.

yeah i was wondering about that too... you can't really orbit the Earth at anywhere close to the speed of light because it is way higher than the escape velocity. in fact you can only orbit a black hole at that speed.

OutKlast
08-20-2010, 02:30 PM
You got it backwards, the earth would be overloaded with the information if anything, if communication were to happen (e.g. I transfer 1mb of information to the spaceship from earth in one day, it takes 71 days to receive it (easy transfer). The spaceship transfers 1mb of information to earth in 1 spaceship minute = 1/70 minutes on earth).

You sure?

Another diagram (also not to scale):

http://www.outklast.com/misc/comms.gif

Blue line - earth side
Red line - spaceship side
Light purple - communication from earth to the ship
Dark purple - communication from ship to earth

The beige cone is a visual representation (not to scale) of the 'relative' time differential. The space between the two objects is fixed, because it is a circular orbit, therefore distance delay is identical to or from. How could I overload the earth with data? If I send them a webcam stream I will never be able to create enough data when I am experiencing time 'relatively' faster.

If you look at the diagram you can see that information sent from earth to me in the spaceship is condensed. While information sent from me to the earth can have a much greater spread.

Plus the diagram is pretty inaccurate, as maintaining a stable orbit around, say, a solar system at 99.9% the speed of light would require probably light years in radius. So really, there isn't a physically possible way to experiment, and what I said above was theoretical.

Orbiting around black holes may also interest you, OP.

yeah i was wondering about that too... you can't really orbit the Earth at anywhere close to the speed of light because it is way higher than the escape velocity. in fact you can only orbit a black hole at that speed.

You can't travel at 99.9% the speed of light yet either. This is more of a theory exercise. But to acknowledge a few things, assuming you can create enough thrust out of an engine to do 99.9% the speed of light, why wouldn't you place a similar engine 90* to the primary and fire that at slightly less power to create an arc? Also, as I mentioned my diagram is not to scale. I'm not saying you'd orbit at the distance from say earth to the moon. It would probably be much, much greater.

Escape velocities would be an issue if you only used a single directional force and attempted to use the gravitational pull of another object to create arc. Also, the show touched on the possibility of creating a "rollercoaster" in space of sorts that would hold a ship in place. Again, all theory, let's focus on the communication/time issues for now and forgo the "how to build a forward time machine" for another thread.

OutKlast
08-31-2010, 07:38 PM
bump. Also, I don't think the time differential is constant. In other words the longer the travel at light speed the longer the differential.

http://www.lolcatpics.com/images/interesting.jpg

MiKey4
09-01-2010, 01:32 AM
Some points to consider (<--- physics grad student):

1. Special relativity (the model you are using) deals with inertial objects = objects which are not accelerating. Stuff moving at 5mph and such, not changing their velocity. In your example the spacecraft is in orbit, and so it is accelerating- this means you cannot use special relativity.

2. Orbits work in the following way: there are TWO degrees of freedom for an orbiting object. You can chose any two of the following: (a) orbital speed, (b) orbital radius, (c) orbital acceleration, and the third is determined by the previous two. This means if you say "the orbital radius is X and the orbital speed is Y", (like you did), then the orbital acceleration is not up to your to chose. There already exists a single value which gives it that speed and radius.

What I am saying is there is a certain gravitational field that will make something orbit at that distance and speed, and it is a hell of a lot more gravity than the Earth could provide. Simply... that orbit is impossible, it is FAR too fast.

Point 2 is practical, and point 1 is theoretical (and more interesting): something in circular orbit does experience time dilation but not in quite the same way as you might think from special relativity. Check this out.
http://en.wikipedia.org/wiki/Gravitational_time_dilation