MadSci Network: Physics


Date: Tue May 23 17:36:49 2000
Posted By: David Richardson, Post-doc/Fellow, Physics, Williams College
Area of science: Physics
ID: 957477677.Ph

Your question reminds me of a Discovery channel show, about non-lethal weapons in the future. In it they stage a hypothetical siege, where a small house surrounded by freshly cut fields contains some armed fugitives. It shows two snipers wearing clothes that contain optical fiber in such a way that the light on one side of the soldier is collected by the fiber and transmitted to the other side, essentially making them invisible. The fiber would do the bending of the light (by collecting it and guiding it) that you mention using a gravitational field for. (They actually show that they'd look a little like humans but nothing that could be distinguished from a heat haze.) They do the same for a vehicle, again using optical fiber.

So the potential for making someone invisible is there, though putting the theory in to practice and making the invisible man possible is a lot more tricky.

As for the crushing of someone trying to cloak themselves using a gravitational field. I would say, though I haven't done any numbers, that the person would be crushed. I would suggest looking up the experiment that proved Einstein's Theory of General Relativity, in which during an eclipse, a star was seen to move position as the sun passed in front of it. Using the deviation of the star and the sun's gravity, you could get a guess at the gravity necessary to bend the light, say, 30 degrees.

However, it's a little more tricky than just having one set of gravity to make you invisible.

A gravitational field would only attract the light. So to bend the light that is coming straight towards your spine behind you, so that it looks as if it has passed right through your body would entail 3 gravitational fields. (And this would only make your front and back invisible, you could still be seen from the side.)

The first would be somewhere behind you and to, say, your right. This would bend the light out from behind you and shoot it over to your right side.

The next field would be around you, so that it would bend the light so that it would curve around your body.

The final field, somewhere to your right out in front of you, would straighten up the light beam so that it is following the same path as the initial beam.

Just one field around your body would cause a focusing effect. That is, the light coming from either side of you would be attracted to your body. Assuming it didn't hit you, the light would pass you, and the beams from either side would be converging until they actually met (ie were focussed). You can actually see this in nature. If you do a search on the web for the phrase, "GRAVITATIONAL LENS", you would find several sites that display pictures of stars that have increased in intensity for a period for no apparent reason. The deduction is that a massive object has passed between us and the star emitting the light, and caused the light beams passing it to focus due to its gravitational field.

Of course, the gravitational invisible suit would be greatly simplified if there was something out there that repelled light, but as yet, I haven't heard of anything.

I hope this answers your question.

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