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cadmonkey
2002-Feb-19, 10:58 AM
On the subject of sending information faster than light, I came
up with the idea of having a very long stick, about 1 light year
in length.

You could use this stick to 'poke' information to another person
1 light year away. ie (morse code).

If I move the stick forward at one end, doesn't the other end move instantly. Where as light would take 1 year ?

Also, does this mean I could prod receiver in the ribs before he could actually observe me move the stick?

I guess this would apply over shorter distances (smaller stick).

GrapesOfWrath
2002-Feb-19, 11:54 AM
On 2002-02-19 05:58, cadmonkey wrote:
If I move the stick forward at one end, doesn't the other end move instantly.
No.

Even if you hit it with a hammer, and it rang like a bell. How long do you think it would take the sound to reach the other person? Poking it would take just as long. That's how fast the individual molecules can transmit such disturbances.

2002-Feb-19, 01:14 PM
<a name="20020219.6:39"> page 20020219.6:39 aka FAR OUT
On 2002-02-19 06:54, GrapesOfWrath wrote: TO: 2-2-19

On 2002-02-19 05:58, cadmonkey wrote:
If I move the stick forward at one end, doesn't the other end move instantly.
6:40 A.M.#1 My dream? suggest Biggers "NOT" better
try lifesavers instead
Even if you hit it with a hammer, and it rang like a bell. How long do you think it would take the sound to reach the other person? Poking it would take just as long. That's how fast the individual molecules can transmit such disturbances.
6:41 A.M.#2 cut a magnetic line of force
-------------/cut/------ and see if its detected at the ends Quickly?

Chuck
2002-Feb-19, 01:33 PM
Make a rope of superstrings tied end to end. Pull it tight, then tug it to send messages.

cadmonkey
2002-Feb-19, 01:43 PM
Hmm, I thought that may be the case.

So molecules in the stick react to movement not in unison but one after the other, like a wave i.e not instant.

So on a small scale any object ( eg toy car) when pushed from the rear, the front will never move quite at the same time.

Maybe the speed of light barrier is there to stop everything happening instantly.

Donnie B.
2002-Feb-19, 02:09 PM
I've heard the statement that time exists to keep everything from happening at the same moment.

The lightspeed barrier is a bit more subtle. It prevents things from happening everywhere at the same time.

TinFoilHat
2002-Feb-19, 02:20 PM
Remember, objects are made solid by interaction of electromagnetic forces between the valence shell electrons in the atoms making them up. Propagation of forces through a solid object takes place via the same force that makes up light itself. So if you push on one end of a very long stick, the information that it's been pushed on can't propagate through the stick faster than the electromagnetic force can travel.

Argos
2002-Feb-20, 11:41 AM
So molecules in the stick react to movement not in unison but one after the other, like a wave i.e not instant.Maybe the speed of light barrier is there to stop everything happening instantly.


Cadmonkey. I think you should ask them what if the stick were made of an absolutely rigid material. Something that would allow for only an infinitesimal movement (if so) of the molecules in reaction. I think you need a more substantial explanation - which I can't give /phpBB/images/smiles/icon_biggrin.gif - don't you?.

GrapesOfWrath
2002-Feb-20, 11:54 AM
On 2002-02-20 06:41, Argos wrote:
I think you should ask them what if the stick were made of an absolutely rigid material.
I think you should ask them about rotating that lightyear-long stick, just once a year or so. The end of it would be moving pi times the speed of light.

Argos
2002-Feb-20, 12:42 PM
On 2002-02-20 06:54, GrapesOfWrath wrote:


On 2002-02-20 06:41, Argos wrote:
I think you should ask them what if the stick were made of an absolutely rigid material.
I think you should ask them about rotating that lightyear-long stick, just once a year or so. The end of it would be moving pi times the speed of light.


Waaal! That's what I call an impossible Speed.

Anyway, paradoxes are funny. I like to play with them to the limit. It makes me recall my teen years, when It seemed that every theory I heard of had flaws.

By the way, I asked myself the question about the big stick in those years. The difference is that I thought of an unidimensional stick, which had no mass ( a highly metaphysical one - now I know that such stick does exist and is called ray of light). But I never had the courage to speak out my question, fearing that some one could consider me dumb (which wouldn't be an exaggerated supposition at all).

I'm glad to see Cadmonkey do the same question. It is a great indicator of the amazing capacity of the human race to have similar (though often wrong) thoughts, even separated by thousand miles.


<font size=-1>[ This Message was edited by: Argos on 2002-02-20 08:05 ]</font>

GrapesOfWrath
2002-Feb-20, 01:06 PM
On 2002-02-20 07:42, Argos wrote:
By the way, I asked myself the question about the big stick in those years. The difference is that I thought of an unidimensional stick, which had no mass. But I never had the courage to speak out my question, fearing that one could consider me dumb (which wouldn't be an exaggerated supposition at all).

Of course! The massless stick.

Take a laser light and shine it into space for a few years, while slowly rotating it twice a year. The tip of the beam will be the tip of your "stick." At the end of six months, check out the tip of the beam. It will rotate pi lightyears in one year.

<font size=-1>[Fixed errors in description]</font>

<font size=-1>[ This Message was edited by: GrapesOfWrath on 2002-02-20 08:11 ]</font>

cadmonkey
2002-Feb-20, 01:28 PM
Okay forget the stick, how about a disk/cylinder with a radius of 1 light year?

If rotated by being driven from the centre how much of delay would there be before the outer edge of the disc began to move?

Would the disc even move at all as the outer edge would have to move at light speed and would therefore have infinite mass?

Another Phobos
2002-Feb-20, 04:08 PM
Great answers to these types of questions...
http://math.ucr.edu/home/baez/physics/
(look under the Cosmology/Relativity sections)

Argos
2002-Feb-21, 11:21 AM
On 2002-02-20 08:06, GrapesOfWrath wrote:
Take a laser light and shine it into space for a few years, while slowly rotating it twice a year. The tip of the beam will be the tip of your "stick." At the end of six months, check out the tip of the beam. It will rotate pi lightyears in one year.


It seems to me that a rotating stick made up of light would display a spiral propagation pattern.

Say the length (radius) you want for the stick is 1 LY, and the rotation is 360 deg/year. When you turn on the beam and starts the rotation, every photon will be sent into a different fraction of radian. After 1 year the beam will be pointing to the same direction it was one year before, while the first photon arrives at the spot of destination, becoming the tip of the stick. Thence, you would need a spiral to link the dots (photons) which make up your stick, in a two dimensional plane. To avoid violation of c, the tip of the axis of the beam may rotate 2 pi lightyears in one year, but not the actual beam.

This fact presents a problem when it comes to receiving electromagnetic waves from a rotational source (or, conversely, receiving with a rotational sensor/antenna). The more distant the source and the more fast it rotates, the lesser is the time you have to capture the photons.

As to the 1 LY radius disc I think that it would happen as follows: your disc has a central axis which will provide the drive from an engine. Once you start the engine which makes the disc rotate, the drive – i.e., the information on the movement of the axis - will begin propagating throughout the disc at a speed lesser than light’s. No movement will be perceived in the disc until the driving force reaches the outermost limits of the disc. You'd have to adjust the engine so that it didn't over stress the material of the disc. And your engine would never have the strength to make the fringes of the disc exceed c, no matter how powerful it were.

Am I right?

Bob S.
2002-Feb-21, 05:02 PM
No movement will be perceived in the disc until the driving force reaches the outermost limits of the disc. ... And your engine would never have the strength to make the fringes of the disc exceed c, no matter how powerful it were.
Am I right?

Mmm, almost. All materials exhibit elastic and sometimes plastic properties. The disc has inertia which would resist motion at first. The torque of the motor would start to turn the inner part of the disc, creating lines of shear spiraling out, creating initially elastic strain on the inner disc area. It would start to resemble a whirlpool with the outer edge barely moving while the inner part spun tighter and tighter. At some point your disc would exceed its elastic modulus limit and start plastically deforming and finally rupturing, no doubt long before the outer edge reached anything close to c.

You can model it on a small scale. Lay out several hundred square yards of aluminum foil (aluminium for your Brits) on a giant air-hockey grid to reduce ground friction, attach a fan blade and motor to the center, crank it up and see what happens. But don't ask me to help clean up the mess!

Pi Man
2002-Oct-08, 08:01 PM
Try falling into a black hole, narrowly missing the singularity and coming back in time in order to send the message before you knew that you wanted to send a message!

JS Princeton
2002-Oct-09, 06:27 AM
Nah, Pi Man, there's no gaurantee that you'll come out in this universe (or that you won't be bombarded with highly energetic blueshifted photons that will destroy you in any case).

Argos
2002-Oct-09, 01:44 PM
On 2002-10-08 16:01, Pi Man wrote:
Try falling into a black hole, narrowly missing the singularity and coming back in time in order to send the message before you knew that you wanted to send a message!



I thought that there were no means of missing the singularity./phpBB/images/smiles/icon_smile.gif

(*)If i'm right, missing the singularity was once the pillar sustaining the argument that the big-bang was an illusion, and the universe was cyclic; a previous universe would come crunching so that, in the final moment, the trajectories of the particles would pass tangent to the very point of the would-be singularity and emerge on the other side expanding in a newly born universe. That would leave the impression that the expanding matter originated from the same point. But as we know, recent developments in cosmology rule out this idea for the time being.

(**) The "ressurection" of threads shows how the members are tuned in! It's very pleasing to review topics and add new impressions. /phpBB/images/smiles/icon_wink.gif

<font size=-1>[ This Message was edited by: Argos on 2002-10-09 09:54 ]</font>

JS Princeton
2002-Oct-09, 01:48 PM
I don't know that the DeSitter Waist has been observationally disproven.

Also, if you have a non-Schwartzchild blackhole (one with angular momentum or charge), you can plot a path that does not necessarily intersect the singularity. This is not possible to do with the Schwartzchild blackhole.

Argos
2002-Oct-09, 01:59 PM
On 2002-10-09 09:48, JS Princeton wrote:
I don't know that the DeSitter Waist has been observationally disproven.

Also, if you have a non-Schwartzchild blackhole (one with angular momentum or charge), you can plot a path that does not necessarily intersect the singularity. This is not possible to do with the Schwartzchild blackhole.


Does this mean that a cyclic universe is still possible?

Was the primordial "universal black hole" a non-Schwartzchild blackhole?

JS Princeton
2002-Oct-09, 02:29 PM
The primordial atom theory of the Big Bang is nearly unprovable at this time. Before the time of last scatter, we have very little observational evidence for what the universe was like. There are plenty of models available, but as far as I know no one has a good handle on which one is right. They all have to conform to the basic observations of the Big Bang, namely the cosmic abundances of light elements, the hubble flow, large scale structure measurements, and the CMB features. These are all very much after the fact features of the Big Bang.

Certain cyclic models have been discounted, but the "bounce" at the DeSitter waist I think is still available. I may be wrong on that one though.

There's no observational evidence that the universe is either spinning or has net charge which would both (barring some strange inflationary effect) have observational consequences today if the "black hole" was non-Schwartzchild. That said, nobody really knows what was going on beyond z=1000 other than from theory, so I guess it could be the case.

Pi Man
2002-Oct-09, 10:33 PM
I thought that there were no means of missing the singularity./phpBB/images/smiles/icon_smile.gif

I heard you could fall past the event horizon of a black hole and still miss the singularity from Professor Alex Filippenko (http://astron.berkeley.edu/faculty_pgs/filippenko.html). Take it up with him! /phpBB/images/smiles/icon_biggrin.gif