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Space and Time Discussions on space, time, relativity, physics, and the nature of the universe.

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  #1  
Old 10-24-2009, 11:51 AM
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Meeting Point with an E.T.

Let us suppose that we discover today an Extra-Terrestrial civilization with a similar knowledge with us, on a planet distant from the Earth only 3 light-years away. What a chance to have found them, let's send immediately a message and organize a Meeting somewhere, preferably at half the distance, in order to minimalize the expenses.
We (the humans) are at point A, in the center of the following diagram, today. We see our E.T. friends on point B, 3 Liht-years away (it is a distance), and of course, as they were 3 years ago. See the diagram below.



The message we are sending to them goes through space at speed=Speed Of Light.The message says who we are, where we are, & that we'd like to meet on point C of Space, at half the distance. The message gives also the instructions on how to build a spaceship capable of travelling at half the Speed Of Light (we cannot actually do that for the moment). The message is sent today, the E.T's will receive the message in 3 years from now, when they will reach point B'. The E.T civilization have a year to build the spaceship. They will send the expedition from point B", and reach the Meeting Point at C'''.In the meanwhile, 7 years will have last, from our point of vue, between the discovery and the meeting with our E.T. friends.
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Old 10-25-2009, 09:58 AM
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Old 10-25-2009, 06:46 PM
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I believe from this simple example that it is well understood that we cannot communicate with our E.T's in TODAY's space.
Also, they are not in point B anymore, we know that. Point b resides in the PAST.
Also, we know that they are not in point B', because point B' is in the FUTURE.
So, we know that our E.T.'s are into TODAY's space, the PRESENT, but we have no ability to see or communicate with them.
We can extend this, and say that we CANNOT SEE ANYTHING THAT IS IN THE PRESENT.
I hope it is clear to everybody.
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Old 10-26-2009, 04:19 AM
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Predictions. Mathematical predictions. We would be able to calculate where to aim our signal. And why would you use a beam? It would be better to use a spherical emission.

And that is just silly, of course if something is so many light years away and when it reaches us, it is not its "present".
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Old 11-18-2009, 01:58 AM
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Yes Michel, that makes sence.

Every image which arrives at our retinas is an image that was sent some time ago. If from the stars, it was sent years ago.

But that doesn't mean that we are at a different point in time. All matter exists at all points in time at the same time, though it is moving through time at different rates.

This is a little difficult to imagine so try it this way. If an object were to exist at point x,y,z and at time t. If it is moving in the x axis at 1/2 c then in one second it is at x+1/2c, y, z, t+C

Thus if two objects were to start very near each other and move away from each other one at 9/10 c and the other at 1/2 c for a given amont of time. Then turn around to move back toward each other each still at the same speed. They would both arrive back very near x,y,z in space. But because one was moving at 1/2c and the other at 9/10 c they moved through the t axis at different rates.

So when they both arrive back very near to x,y,z they would be at far different points along the t axis. Thus though they would be next to each other in 3D space, they would still be very distant from each other. Distance in time is the same as distance in space.

They would be standing next to each other but could not reach a hand out to touch each other. This is not what we expirience in scientific observation.

This is answered by the fact that all matter exists as a long strand occupying the whole of the t axis. Thus both objects were moving through time at different rates, but both are still very near each other at the end of their return trip.

Jerry
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Old 11-18-2009, 02:13 AM
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My post would be more clear if I include the relatavistic transform for time dialation in the paragraph starting thus. This paragraph should read. I tried to edit but it was too late.

This is a little difficult to imagine so try it this way. If an object were to exist at point x,y,z and at time t. And stands till in 3D space for 1 second it is then at x,y,z,t+c If it is moving in the x axis at 1/2 c then in one second it is at x+1/2c, y, z, t+sqr(1-0.5^2)C or t+0.86c because its rate of travel through time is reduced by the relatavistic speed in space.
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Old 11-18-2009, 07:39 AM
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Quote:
They would be standing next to each other but could not reach a hand out to touch each other. This is not what we expirience in scientific observation.
I have to strongly disagree with that.
In the place I live today, there were dinosaurs living, some time ago. I cannot reach them. They cannot reach me. I cannot see them, and they cannot see me.
You cannot see your friend sitting on the same chair you are sitting right now.
By the same way, you cannot see yourself a second ago. And you cannot see yourself a second in the future.

But you can see your friend sitting on a chair next to you, as he was a few milliseconds ago. To speak more clearly, you can only but see your friend as it was a few milliseconds ago; you cannot see wathever you want.

In your example of the moving objects, in order for the 2 objects to meet, the faster one will have to stop and wait, otherwise they will never meet.
Think of it as an appointment.
You have an appointment with your friend at Central Square tomorrow at 11.00 am.
You go there slowly, and get to Central Square right in time, at 11.00.
Your friend, who has a Ferrari, got to the Square at 10.00, met a nice girl (he has a Ferrari), and went away. Wil you ever meet with your friend? In order to meet, you have to be both in time and in space at the same place.

But the most important to me is that you cannot see your own past. That's a fact that most of the people I try to discuss with do not quite understand.
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Old 11-18-2009, 08:55 AM
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Speaking more scientifically, we could say this:
Any observer, in order to determining events in his observable world, needs 4 coordinates x,y,z,t.
Any observer, in his own frame of reference, lives at his own t=0, which gives him the impression of living in a world of coordinates x,y,z only, a phenomenon we call "3d space". Coordinate t vanishes because observer's t=0 , a phenomenon we call "the present".
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