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The Magic Cafe Forum Index » » Not very magical, still... » » Laser travels faster than speed of light! (0 Likes) Printer Friendly Version

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landmark
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This is a great discussion and I'm learning a lot. Still surprised that I never realized that the movement of a wave through an object is the same as the speed of sound.
Anyway, about the dot. How come the change in position doesn't carry information? If HERE then do A, If THERE then do B, else C?
acesover
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MobilityBundle.

I have a question for you. But first let me say that your knowledge on this far exceeds mine. So here goes with a question that may or may not make sense.

If what you say you have your thingy traveling faster than the speed of light in a straight line, and I have a solid object traveling at the speed of light also in a straight line starting from point A and I give it a second or two head start, can you explain to me how with your example it will catch up with my object and reflect off of it. In other words bothobjects start off at point A but at different times miine leaving say 2 seconds before yours. Or does your example only work with an intersetion point?

Please excuse what may e a simplistic question.

Again this is interesting.
If I were to agree with you. Then we would both be wrong. As of Apr 5, 2015 10:26 pm I have 880 posts. Used to have over 1,000
MobilityBundle
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Good questions.

Landmark: The red dot does carry information, in the way you suggested. To make things a little more concrete, suppose you, me, and Acesover are standing in a triangle, each separated from each other by 10 light years, and we all have lasers. Based on what's been said above, we've established that any of us -- you, say -- can make your laser's red dot sweep out a path from me to Acesover in any time you like -- say, one second.

But Acesover's clarification above is that, from the moment you decide sweep out such a path, it will still take 10 years for your laser's red dot to get to me, and 10 years + 1 second to get to Acesover. Moreover, the information carried by the red dot is information from you. If I wanted to send a message to Acesover, I couldn't do it in one second using your laser. For example, I couldn't "pin a note," literally or figuratively, to your laser's dot before it goes zipping on its 1 second journey over to Acesover. I'd have to use my own laser, and that would take another 10 years.

That's the sense in which the red dot carries no information -- it carries no information from anyone but the guy controlling the laser. (And that information is carried at light speed.)

----

Acesover, suppose still that you, Landmark, and I are standing in the triangle each separated by 10 light years. Right now, my laser is shining on you. Soon, you're going to send an object from you to Landmark at light speed, and you want my laser to overtake it and reflect off of it exactly half way on its journey. Except for the little footnote I'll mention at the end, that can be done. But it will have to be arranged far in advance:

1. Let's say you plan on launching your object at midnight, 1/1/2040. It will arrive at Landmark at midnight, 1/1/2050, and the midpoint of that trip is midnight 1/1/2045.

2. In order for my dot to be shining on your part of the triangle, I have to start shining my laser at you no later than midnight, 1/1/2030, because the laser takes 10 years to reach you.

3. And in order for me to know your launch date, you have to send me a laser-message by no later than midnight, 1/1/2020, because your message will take 10 years to reach me.

Suppose all that happens. Now, what do I have to do to make sure my laser hits your object at the designated time of midnight 1/1/2045? Well:

4. Consistent with step 2, I start shining my laser on you at midnight 1/1/2030. Since your object gets a 2 second head start, then at 00:00:02 AM, I start slowly rotating my laser towards Landmark. How slow? Well, we're on an equilateral triangle, so it's 60 degrees from you to him. And I want my laser beam to overtake your object exactly halfway. So, starting at 2 seconds after midnight, I rotate it 30 degrees over a 5-year-minus-two-second time frame. That's about 6 degrees per year, or about a degree every two months. To be sure, that's a difficult engineering problem, although I think even with existing technology we can get that level of precision.

With all those careful arrangements, presto, my dot will overtake your object exactly halfway on its journey. But two kind of sloppy things to clean up:

A. In referring to times and dates above, I've kind of assumed we're all on a synced up calendar. In general, it's impossible to sync clocks of people in relative motion, but fortunately, we're assuming we're all not in relative motion.

B. It's technically impossible for a solid object to travel at light speed. But your question (and I hope my answer) still makes sense.
landmark
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Thanks MB. A pleasure to read your explanations.
MobilityBundle
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No problem. This stuff is probably one of my favorite topics in physics... always glad to talk about it!
Matze
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Quote:
On 2011-08-20 07:48, Michael Daniels wrote:
Quote:
On 2011-08-20 07:38, MobilityBundle wrote:
For example, a shadow can travel faster than light. Or if you imagine a giant pair of scissors closing, the point at which the blades meet can travel faster than light, if the scissors are big enough.


Umm - No.

Mike


Umm - Yes

Matze
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