Seeing the past: A somewhat realistic idea

[devonin]

Re: Seeing the past: A somewhat realistic idea

Ah, the thing he's referring to is the way that the passage of time is subjective, and that such subjectivity is quite noticable as you start dealing with speeds like the speed of light.

If you got into a ship and moved away from the earth at the speed of light for one year, and then turned around and came back at the speed of light for one year, you would find that far more than two years had passed in the subjective existance of people who were on the Earth, while you would have experienced only two years of your own subjective time passing.

Currently, we're nowhere near the level of technology to come close to such speeds. As I mentioned above, the person who has spent the most time in orbit and in space moving at very high velocities is only a fraction of a second younger than he would have been had he stayed on earth his whole life, but the principle is (theoretically) pretty well understood.

[Relambrien]

Re: Seeing the past: A somewhat realistic idea

Think of it this way. Everything we can see, we can see because of light.

So if you start at some point A, and travel faster-than-light to point B, it will still take some time before the light from where you started reaches point B, so the light currently at point B is from events that occurred prior to your departure. Meaning, you've just arrived at point B before you left point A. You could theoretically see yourself leaving.

Another way to think about it is through a layman's description of relativity: as you approach the speed of light, everything seems to slow down. You get faster, everything appears to be going slower, hence "relativity." So what happens when you break the speed of light? At the speed of light, everything would seem to stop. Past that, it would seem as if everything is happening in reverse.

The problem is that the speed of light seems to be the absolute maximum speed at which anything can travel in our universe, just like the Planck distance seems to be the absolute minimum unit of distance. Apparently there's been mathematical research done on both of these, but it's all beyond me, and I don't understand it. Thus, going faster than light would require circumventing our universe, either through using extra dimensions or establishing a universe within a universe.

Oh, I thought of another example. Let me try and develop it.

Say you have two clocks, both reading 12:00. They sit at some point A for 30 minutes, so that each reads 12:30. Clock I travels to some point B faster than light, and takes five minutes at Clock I's time. Thus, it reads 12:35. Light takes 10 minutes. Because light takes ten minutes to reach point B, Clock I observes point A as it was ten minutes ago. Since Clock I reads 12:35, it is observing events that occurred at 12:25. It sees itself and Clock II both reading 12:25 at Point A. Thus, it just traveled five minutes into the past.

[devonin]

Re: Seeing the past: A somewhat realistic idea

Thus, it just traveled five minutes into the past.

I would instead argue: Thus, you have the perception that it travelled five minutes into the past. You've only time travelled if you insist that your subjective personal time is the "correct" time, and thus you are seeing things "before they happened"

If news of a war breaking out in china doesn't reach me until 7 days after the war has started, I'm hearing about "events of the past" but that doesn't mean I've travelled through time, and while I get that somehow "light getting here" and "some guy getting here" aren't necessarily the same thing, I think the point holds.

The real point to make here is that time is a manufactured system that we use to measure the relation of events to other events. It doesn't necessarily "exist" as an objective concept outside the bounds of humanity.

I mean, going back to the classic person in spaceship example. I feel as though I've time travelled into the future because in two years, when I return to earth, 20 years have passed. But the point is, they -did- pass, you didn't time travel, you waited it out in a non-traditional manner. From the standpoint of the people on earth, you didn't time travel, you went into stasis, so that 20 years later, you came back only aged 2 years.

I mean, who is correct in this case?

[Relambrien]

Re: Seeing the past: A somewhat realistic idea

Forgive me for not explaining more thoroughly; I meant that from the clock's perspective, it traveled five minutes into the past. I agree with you of course.

[devonin]

Re: Seeing the past: A somewhat realistic idea

I mean, by a certain standpoint, going to sleep allows me to travel 8 hours into the future.

[Rolenquin]

Re: Seeing the past: A somewhat realistic idea

I don't know if I understand your original post in its entirety, but here are some things you might want to keep in mind:

the speed of light is a constant, finite, and not relative; meaning that no matter how fast you're traveling, light will always be going at the speed c, therefore it is not plausible to go faster than the speed of light.

as for group experiments with lasers that "exceed" light speed but no information is transfered: It is kind of cheating and I'll explain why. To put it in laymen terms it's almost as if the lasers are running a relay race. Once the beam from one laser reaches a point, the next is started and so on and so fourth. So while the group of lasers combined speed exceeds that of light, no single one does therefore making the transmission of information impossible.

[devonin]

Re: Seeing the past: A somewhat realistic idea

the speed of light is a constant, finite, and not relative; meaning that no matter how fast you're traveling, light will always be going at the speed c, therefore it is not plausible to go faster than the speed of light.

The basic premise of the post supposed the eventual ability to do so. Obviously if you claim that under no circumstances can that ever happen, the theory falls apart, but the joy of thought experiments is that you can assume things simply to see where they might lead.

[skishmonkey72]

Re: Seeing the past: A somewhat realistic idea

On teleportation: I won't say anything about the actual idea of teleportation, but when you mention using teleportation as a means to transport humans, it becomes a whole different matter. The question becomes: Is human life a collective state of all the particles of your body, or is it something completely intangible that cannot be represented by the state of one or more particles?

About observing past events: Not only would the camera or recording device have to travel out into space and back faster than the speed of light, this still poses a few more problems. As was mentioned before, there are obvious visibility problems such as other matter being in the way of viewing the earth or parts of it. But the earth's rotation also would make it so that you would not only have to be travelling towards and away from the earth incredibly fast, you'd have to orbit it at the same time, which, at a distance of 20 000 light years away, would be even more unfeasible. Spending just a day at that distance focusing on one part of the earth would involve travelling at speeds of:
pi * [(20 000 light years)/2] / 24 hours --> convert to m/s and you have one fast ****er.

Wait... I'm not trusting myself at the moment, anybody want to verify that almost-equation is in fact correct?

To put it in laymen terms it's almost as if the lasers are running a relay race. Once the beam from one laser reaches a point, the next is started and so on and so fourth. So while the group of lasers combined speed exceeds that of light, no single one does therefore making the transmission of information impossible.

This doesn't make sense to me. If the individual lasers are travelling at subluminal speeds, even with zero downtime between a laser reaching the point and the next laser starting, you've still got lasers going at less than the speed of light. To achieve speeds higher than the speed of light you'd have to have to start the next laser before the previous is finished.

Did I interpret that right?

[Rolenquin]

Re: Seeing the past: A somewhat realistic idea

sorry, I phrased it a bit wrong... read the wikipedia article under Group velocities above c on this link... that's what I meant to describe.. http://en.wikipedia.org/wiki/Faster-than-light

[bender5]

Re: Seeing the past: A somewhat realistic idea

My problem with this whole thing is, even in the event of faster than light travel I don't get how it would be that humans could take advantage of it. Say you send said robot 10 years away but beating the light there by 10,000 years. If it were possible to travel at that speed I highly doubt anything that anything could possibly pick up would be enough to piece together something usable and watchable. Maybe a glimpse at continental shifting, or a casual spot of the revolution of the Earth of yesteryear before history was recorded. There isn't really a logical way of making sense of it. No matter what kind of image you would get if the ship were to start recording as it leaves Earth on it's way to it's destination and back. If it does as you say beat the light to where ever it is that you are going, and the entire thing would work. How would we then watch this footage. Even if you could see everything as it happens. It would take say 10-50 years to even get the footage, and then what? You would have 10,000 plus years of Earth's history, and then you would be filtering through the 10,000 years of footage just to put yourselves 10,000 years more behind. Sure it would be interesting to look back in time, but to fully optimize this concept there would have to be some way to filter through the footage at super speed to see anything useful.