- #1

AtomicJoe

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What is the shortest distance you (or anything) and travel?

Is there a limit?

And if so why?

Is there a limit?

And if so why?

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- Thread starter AtomicJoe
- Start date

- #1

AtomicJoe

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What is the shortest distance you (or anything) and travel?

Is there a limit?

And if so why?

Is there a limit?

And if so why?

- #2

Drakkith

Staff Emeritus

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- #3

AtomicJoe

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Just because you can't measure a shorter distance does not mean you can't travel a shorter distance?

- #4

HallsofIvy

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I can't even figure out what that

Just because you can't measure a shorter distance does not mean you can't travel a shorter distance?

- #5

AtomicJoe

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I can't even figure out what thatmeans! What doyoumean by "measure" a distanced and what do you mean by "travel" a distance?

Well measure is what it says, measure or detect, travel means to move.

I think you can move a distance which you can't measure.

- #6

bp_psy

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- #7

AtomicJoe

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Errr... well you tell me!!

I am not too sure about this uncertainly principle business anyway, it refers to measurement I think, saying basically something like you can't measure things too accurately or whatever.

However I am not bothered about measurement really, I don't care if you can measure the movement or not, I am concerned if their is a lower limit on the shortest distance you can move.

The fact you can't measure it does not mean it didn't move does it?

Eg if I had a mouse in a box, I can't measure where it is moving in the box but it can move nonetheless can't it?

- #8

Curl

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So asking "measure a small distance" turns out to be an invalid question at those lengths.

- #9

AtomicJoe

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So asking "measure a small distance" turns out to be an invalid question at those lengths.

I really do not see that it makes any difference I mean basically if you move something which is " nothing like you are familiar with" then it is "nothing like you are familiar with" in a different place".

I mean we move things everyday which are full of fundamentalist particles with out any problem.

- #10

Gabe21

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everything is always moving even if it appears still.

- #11

Pengwuino

Gold Member

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I really do not see that it makes any difference I mean basically if you move something which is " nothing like you are familiar with" then it is "nothing like you are familiar with" in a different place".

I mean we move things everyday which are full of fundamentalist particles with out any problem.

You don't see how the movement occurs at the [tex]10^{-35}m[/tex] scale, however.

Think of it this way, let's say you have a grid of tiles on the floor and someone wants to move across them and they're all 1'x1' and you're looking at this person way up in the sky. Now, the person can continuously move himself across those 1x1 tiles. He can make a movement that is so slight that the doesn't change his position to a neighboring tile (let's say he only moves an inch).

At the Planck level, this notion no longer is valid. "Small movements" such as in the previous example do not exist. It is also something fundamental, it is not just an issue with our experimental abilities. The guy in the previous paragraph could use a telescope to try to get a better measurement of how the guy is moving with a finer resolution than the 1'x1' tiles because the guy on the tiles can make seemingly continuous motions. At the quantum/planck level, such ideas are meaningless. Everything is discrete.

- #12

AtomicJoe

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You don't see how the movement occurs at the [tex]10^{-35}m[/tex] scale, however.

Think of it this way, let's say you have a grid of tiles on the floor and someone wants to move across them and they're all 1'x1' and you're looking at this person way up in the sky. Now, the person can continuously move himself across those 1x1 tiles. He can make a movement that is so slight that the doesn't change his position to a neighboring tile (let's say he only moves an inch).

At the Planck level, this notion no longer is valid. "Small movements" such as in the previous example do not exist. It is also something fundamental, it is not just an issue with our experimental abilities. The guy in the previous paragraph could use a telescope to try to get a better measurement of how the guy is moving with a finer resolution than the 1'x1' tiles because the guy on the tiles can make seemingly continuous motions. At the quantum/planck level, such ideas are meaningless. Everything is discrete.

So say use a force and apply it to an object and it moves one plank distance, what happens if I apply the same force to an object with twice the mass, does it move or not?

- #13

Gabe21

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yes. just because u cant measure the distance doesn't mean it didn't move.

- #14

Pengwuino

Gold Member

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So say use a force and apply it to an object and it moves one plank distance, what happens if I apply the same force to an object with twice the mass, does it move or not?

The problem is you're trying to use classical macroscopic ideas to deduce what can happen at scales where classical physics fails immensely. Everything is quantized. At some point, what you call a force can no longer be arbitrarily cut in half as well.

- #15

AtomicJoe

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The problem is you're trying to use classical macroscopic ideas to deduce what can happen at scales where classical physics fails immensely. Everything is quantized. At some point, what you call a force can no longer be arbitrarily cut in half as well.

But you are not cutting the force in half you are doubling the mass of the object the force is being applied to.

That is a perfectly reasonable thing to do, surely? It still need to be explained because of various laws of physics.

What if I apply the force twice, it should move one plank unit then surely, or does the energy simply disappear breaking a conservation (of energy) law?

- #16

AtomicJoe

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yes. just because u cant measure the distance doesn't mean it didn't move.

In which case you could say there is no minimum movement distance?

- #17

HallsofIvy

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Okay, whatWell measure is what it says, measure or detect, travel means to move.

I think you can move a distance which you can't measure.

- #18

AtomicJoe

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Okay, whatreasondo you have to think that?

Well say I put a mouse in a box, it moves around, but I can't measure it.

- #19

saim_

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The above is right in a metaphysical sense or from a realist's point of view, but, within the framework of current physics, you can never tell if something moved a distance smaller than Planck's length and thus it becomes meaningless, in terms of physics, to ask if something can "really" move a smaller distance. Maybe it can, maybe it can't; physics can't tell you, so, for physics a smaller distance doesn't exist (as of yet, of course).just because u cant measure the distance doesn't mean it didn't move.

- #20

AtomicJoe

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In fact I would go as far as to say I *know* it has moved, the evidence is overwhelming.

- #21

saim_

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The force applied will accelerate the particle and deform its wave-packet or its probability distribution function. Taking approximation of the gravitational effects of the energies involved into account will further blur our view of the position and velocity of the particle. Things are not so simple at quantum scales.

http://rugth30.phys.rug.nl/quantummechanics/potential.htm [Broken]

http://en.wikipedia.org/wiki/Uncertainty_principle

http://rugth30.phys.rug.nl/quantummechanics/potential.htm [Broken]

http://en.wikipedia.org/wiki/Uncertainty_principle

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- #22

AtomicJoe

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The force applied will accelerate the particle and deform its wave-packet or its probability distribution function. Taking approximation of the gravitational effects of the energies involved into account will further blur our view of the position and velocity of the particle. Things are not so simple at quantum scales.

http://rugth30.phys.rug.nl/quantummechanics/potential.htm [Broken]

http://en.wikipedia.org/wiki/Uncertainty_principle

Thanks, but their is a lot of reading there, but do you basically agree with me or not?

Or are you err.... uncertain?

Basically would you detect a movement of 1 plank length after 5 applications of the force?

That is pretty much a yes or no answers, isn't it?

Last edited by a moderator:

- #23

saim_

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By the way, the idea that Planck's length is the smallest measurable distance is derived from lose approximate calculations that combine QM and GR (please someone correct me if I'm wrong here); it is only conjecture that it might represent the smallest length measurable; it's not a fact of basic QM. But since QM and GR are all we have right now, Planck's length is the limit for current physics.

- #24

AtomicJoe

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It just seems to me if you apply 1/5 of the energy it must move 1/5th of the distance.

- #25

Gabe21

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- #26

saim_

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I think this discussion will do more harm to your understanding than good. So I suggest reading up a little bit on quantum mechanics and then look back at this matter.

- #27

AtomicJoe

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Also if you apply the force at an angle and measure the x and y axis movements you find it has move one plank length yet did not move in the x or y axis at all!!

- #28

AtomicJoe

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I think this discussion will do more harm to your understanding than good. So I suggest reading up a little bit on quantum mechanics and then look back at this matter.

You only seem to be looking at the problem from one point of view. I don't think me reading anything would change my view (although I don't think you were replying to me).

The classical position has to be reconciled with the quantum position because that is what happens in the real world.

Also it says this plank stuff is the subject of research so it is to some extent an unknown area.

- #29

nasu

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yes. just because u cant measure the distance doesn't mean it didn't move.

How do you know that it moves if you cannot measure the distance? To be sure that it moved, the distance must be non-zero.

- #30

Gabe21

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thats like saying a tree that falls in the woods doesn't make a noise just because noone hears it.

- #31

bp_psy

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Quantum physics is what happens in the real world.Classical mechanics has a much more limited scope.The classical position has to be reconciled with the quantum position because that is what happens in the real world.

- #32

mishrashubham

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So say use a force and apply it to an object and it moves one plank distance, what happens if I apply the same force to an object with twice the mass, does it move or not?

I know absolutely nothing about Quantum Mechanics. But isn't Newtonian idea of force just a macroscopic observation of just the fundamental forces? I mean when we apply force on something through contact, at the atomic level it is the electromagnetic repulsive force that causes the body to move isn't it. F=ma only applies for big bodies. But at extremely small distances such as the subatomic scale these things do not hold.

So to be saying that we apply a force to a body so that it moves one Planck length is meaningless. A planck length is [tex]10^-^2^0[/tex] the size of a proton, which itself is [tex]10^-^4[/tex] the size of an atom. Plus the electrons are supposed to form an electron cloud and not a fixed orbit. Therefore atoms are always moving distances much larger than a planck length.

- #33

AstrophysicsX

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- #34

AtomicJoe

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I know absolutely nothing about Quantum Mechanics. But isn't Newtonian idea of force just a macroscopic observation of just the fundamental forces? I mean when we apply force on something through contact, at the atomic level it is the electromagnetic repulsive force that causes the body to move isn't it. F=ma only applies for big bodies. But at extremely small distances such as the subatomic scale these things do not hold.

So to be saying that we apply a force to a body so that it moves one Planck length is meaningless. A planck length is [tex]10^-^2^0[/tex] the size of a proton, which itself is [tex]10^-^4[/tex] the size of an atom. Plus the electrons are supposed to form an electron cloud and not a fixed orbit. Therefore atoms are always moving distances much larger than a planck length.

I think you have to consider the centre of gravity and say applying a small force to large object.

- #35

AtomicJoe

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