Nothing faster than light!

[jungjedi]

The contact point where the two blades meet is not a physical object. So there is no fundamental reason why it could not move faster than the speed of light, provided that you arrange the experiment correctly. In fact, it can be done with scissors provided that your scissors are short enough and wide open to start, very different conditions than those spelled out in the gedanken experiment above. In this case it will take you quite a while to bring the blades together -- more than enough time for light to travel to the tips of the scissors. When the blades finally come together, if they have the right shape, the contact point can indeed move faster than light.

[jungjedi]

An analogy, equivalent in terms of information content, is, say, a line of strobe lights. You want to light them up one at a time, so that the `bright' spot travels faster than light. To do so, you can send a luminal signal down the line, telling each strobe light to wait a little while before flashing. If you decrease the waiting time with each successive strobe light, the apparent bright spot will travel faster than light, since the strobes on the end didn't wait as long after getting the go-ahead, as did the ones at the beginning. But the bright spot can't pass the original signal, because then the strobe lights wouldn't know to flash.

[Boerseun]

The contact point where the two blades meet is not a physical object. So there is no fundamental reason why it could not move faster than the speed of light, provided that you arrange the experiment correctly. In fact, it can be done with scissors provided that your scissors are short enough and wide open to start, very different conditions than those spelled out in the gedanken experiment above. In this case it will take you quite a while to bring the blades together -- more than enough time for light to travel to the tips of the scissors. When the blades finally come together, if they have the right shape, the contact point can indeed move faster than light.

Did you read Craig's reply above? As the scissor blades approach the speed of light, their mass approaches infinity, which means try as you might, it'll take more energy than exists in the whole of the universe to close your scissors at the speed you propose. Which means you simply cannot do it.

[snoopy]

Yes this is an example of a `pattern` moving faster than light.

 

Patterns are allowed to move faster than light. its weird but true.

[Boerseun]

Yes this is an example of a `pattern` moving faster than light.

 

Patterns are allowed to move faster than light. its weird but true.

A pattern isn't material, neither does it carry information. A pattern only exist in the observer's mind. So there's not really anything weird in it, at all.

[snoopy]

To boersun

 

Not all patterns are just in the observers mind a `drawing` is a type of pattern although admittedly you cant send this type of pattern faster than light. You should read Roger Penrose he has some weird ideas about patterns if your interested in tiling solutions and stuff like that.

[arkain101]

:)

Imagine a revolving light source somewhere on the surface of the earth. Instead of a lighthouse beam, let's make it a laser source. Let's locate a specific detector somewhere in space such that it can intercept the beam as it rotates. For simplicity, let's place it out there somewhere around1 million km so that the source doesnt have to rotate faster than, say, 1 RPM.

1. Can the beam swing faster (angular velocity) than 300,000 km/sec anywhere along its path?

2. If it does, can the beam be detected?

 

 

Light that you see that shows a laser beam is not the light from the laser beam.

 

When you see a beam, it is light that has reflected off of dust some kind of sufficient particle for reflecting light, which then has traveled back or towards your eye.

 

So lets pretend this experiment is in a huge dust chamber.

 

Before we make this laser rotate, we turn the light on, in our mind we can imagine a beam shooting through the dust, the beam we see is light that has returned to us.

 

Observer from the location of the rotating laser:

As the laser increases distance, so does the time it takes for the laser light to return to us.(An interesting question to investigate that entered my mind is, does the laser appear to slow down? This is, when we consider it pointing directly away from us.)

 

Now. Lets rotate the laser in the dust chamber.

 

Viewing from above so that we have a circle with a radius. We can clearly comprehend that light closer to the source will reach us earlier, so we will observe a spiraling shaped laser beam, if the chamber is large enough in our mind (1 light year). Although we observe a spiral shaped beam, this is just a picture formed in our mind. What is actually occuring is a series of pathways akin to this.

 

[CraigD]

The contact point where the two blades meet is not a physical object. So there is no fundamental reason why it could not move faster than the speed of light, provided that you arrange the experiment correctly.

Another example of a non-physical “happening” that can propogate faster than c.

 

The scenario can be simplified. Imagine 2 straight-edged objects, separated by a short distance, with edges nearly but not exactly parallel. If the 2 objects move toward one another at a low velocity, not colliding, the point where their edges overlap can be made to “move” at any velocity. For example, for straitedges 0.000000001 radians from parallel closing at 1 m/s, their overlap point “moves” at slightly greater than 3 c, though no matterial part of either straitedge moves faster than 1 m/s.

[jungjedi]

Did you read Craig's reply above? As the scissor blades approach the speed of light, their mass approaches infinity, which means try as you might, it'll take more energy than exists in the whole of the universe to close your scissors at the speed you propose. Which means you simply cannot do it.

 

yes i read craigs reply.im just having trouble wrappinmg it aroundf my brain

[Qfwfq]

Im certainly not going to explain special relativity to you im just going to politely say because there is no `absolute` time and `distance` is relative

There isn't even a need for it...

 

Its a problem where if one considers only classical mechanics that it would provide a mechanism for light to "exceed the speed of light."

 

The beam is revolving at 1 revolution per second. Your equation can be used to compute the tangential speed of a photon at one mile out which would be [math]2\pi [/math] miles per second.

Nope, and not even before Einstein. The beam simply isn't a solid object and the speed of each photon doesn't change once it has left the laser gun, as they don't interact with each other at all. No increase in tangential component with radius, not even according to Newton.

 

to buffy

 

I was actually only joking I dont think the world revolves around me and the rest just gets silly after that so i wont bother replying to it.

What you're replying to here wasn't silly at all, she made some valid points about attitude and remember that if an admin or a mod does this, you either respect it or move along.

 

That seems to mean that the contact point has moved down the blades at the remarkable speed of 10 light years per second. This is more than 108 times the speed of light!

Actually, 10 light years per second would be one helluvalot more than "more than 108 times" the speed of light! How many seconds are there in a year? Anyway you were supposing a tad too much by thinking you could make the snip in the same tenth of a second. Try it with the blades being even just one mile long.

[ronthepon]

Interesting discussion going on here.

 

I note in general that while mass, or information (sent for the very first time) between points A and B can't exceed the speed of light, 'pre-programmed' signals can.

[Qfwfq]

'pre-programmed' signals

Uhm, actually it's a stretch to call it a signal at all. What really happens is that different signals reach different places at nearly equal times, but there is no signal at all between these places.

[ronthepon]

By pre-programmed signal I meant something like: my good pal living millions of light years away will shout "recieved!!", when the little alarm clock I had set to ring millions of years ago there goes off. :rolleyes:

 

Agreed, it's not a real signal transfer.

[Pyrotex]

Imagine a huge pair of scissors, with blades one light year long. The handle is only about two feet long, creating a huge lever arm, initially open by a few degrees. Then you suddenly close the scissors. This action takes about a tenth of a second...

This is an interesting thought experiment. There may be more than one way to answer it, but there is at least this way:

 

The force required to close the scissors in 1/10 second would be greater than the biggest force in the Universe. After all, the scissor blades would be rather heavy. Assuming one metric ton of blades per kilometer, that's over 6 trillion tons, 6*10^12. But don't stop there--your scissors have reverse leverage. You're squeezing the short ends to make the long ends move. Say the handles of your scissors are one meter from the axis of rotation (the fulcrum) and you have a 10^15 mechanical disadvantage. This means you would have to squeeze at least 10^27 metric tons.

 

Okay, let's assume you're the strongest person on Earth and you can squeeze that much. But no material is infinitely rigid. Squeezing the scissor handles is equivalent to "twisting" the ends of two 1 LY long strips of steel. How fast will this "twist" be transmitted down the strips? Not infinitely fast, sorry. The force of the twist will NOT be felt by the entire strip of steel at the same time.

 

The "signal", the detectable "twist" in the steel strip that you initiated at one end of the scissors will travel up the steel strips at some speed much less than c. The far, far ends of the scissors won't even "know" that you closed the scissor handles for many, many years. Those long strips of steel will act as giant springs, or better yet, giant Slinkys. Your force at one end will send a wave-like distortion of the steel up the strips. That "wave" will travel quite fast in steel, maybe a few kilometers per second. But not faster than c.

[jungjedi]

By pre-programmed signal I meant something like: my good pal living millions of light years away will shout "recieved!!", when the little alarm clock I had set to ring millions of years ago there goes off. :P

 

Agreed, it's not a real signal transfer.

 

would this assumption include entangled particles left as a message

[Qfwfq]

would this assumption include entangled particles left as a message

As Bell said (and I remember him saying it in person, when he deliverd a conference where I studied), we can't use the correlation between the states of the two particles as a way of sending messages, since we don't decide either of the two outcomes. However, the violation of Bell inequalities marks that a description can't satisfy the requisite of local realism...........

[jungjedi]

As Bell said (and I remember him saying it in person, when he deliverd a conference where I studied), we can't use the correlation between the states of the two particles as a way of sending messages, since we don't decide either of the two outcomes. However, the violation of Bell inequalities marks that a description can't satisfy the requisite of local realism...........

 

now Im just jealous like when a friend got to meet Robert Rauchenberg and I didnt