Quantization question

[Viviator]

Hello all. This is my first post here, so I hope I don't do anything wrong. I would have posted this in a general 'quick question' forum if there was one, but I figured this would be a good place to ask.

 

So, I've been trying to understand this for a long time, but so far, no one has been able to sufficiently explain it to me. My question comes down to this.

Since quantum theory tells us, there is a smallest significant distance; the planck distance, and thus a smallest possible significant time (The time it would take to move over a distance of 1 planck distance going with the speed of light.) how would 'change' then be possible?

What I mean by that is, that as I understand it now, when a shorter time passes then the planck time, nothing can possibly have changed right? So, you can imagine it like still frames of 1 planck time 'width'. But when you put all those frames side by side you would have one from where everything stays the same, then, directly following that, is the next frame, where again, nothing can change, and so forth. But when we experience the real world we see change and motion all around us. So there is a paradox.

 

I'm guessing I'm misunderstanding the basic concepts here, since that's what happens with most paradoxes, but if not, my other alternative explanations were:

1, Maybe the uncertainty principle makes it possible for something to happen, since the event happening or not is not at a certain point in time, but rather smeared out having probaballistic properties?
2 Maybe, the change occurs instantaneously in between the frames essentially making time grainy and pixel like? (Which would not affect our macro observations)

I really hope someone can explain this to me.

Also on a related question. If massless particles always travel with the speed of light, how does a photon get reflected then? Since at one instant, it travels with lightspeed in the positive direction, and an instant later it would travel with light speed in the negative direction. Or,... there would be a moment in between where it's speed would be 0? Very confusing to me.

Please let me know.
Thanks

Edited December 24, 2013 by Viviator

[Sensei]

When photon is colliding with charged particle, it's absorbed, and later emitted.

Collision can be elastic, which means that newly created photon has exactly the same energy/frequency/wavelength as original.

Or inelastic, new photon has (usually) less energy, and charged particle is accelerated.

Emission of photon takes time. This feature is used by atomic clocks.

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

[swansont]

It might be confusing because that's not what quantum mechanics is saying. Planck units tell you where quantum gravity would be necessary vs general relativity. Not that these are the discrete values that are limits of resolution. Looking at the Planck energy should show you that.

[Mike Smith Cosmos]

Hello all. ....

 

I really hope someone can explain this to me.

 

 

I am not sure if what I say now is going to help your question.

 

The root , rootish of most things is Energy. So although other scientists like Einstein with photo electric effects, Bhor with atoms with electrons buzzing around nuclii, and others . It was becoming clear that energy particularly in its association the the atom, electrons and Photons of light, ,Energy seemed to be in discrete chunks ( digital) rather than a continuous variable.( analogue) . Between them they worked out that with maxwells previous work on Light being an Electro-magnetic Wave that Energy like Light can only exist as Whole Waves . 1,2,3... waves integer number of waves ,the minimum being 1. Plank merely worked out the constant of energy for one wave. namely 6.6260697 X 10 to the minus 34 Joules-sec .

 

So if you want to associate it with particular photons of Light energy say red light , violet light , green light coming from an atom.

 

Energy = h (planks constant ) x Frequency of Photon .

 

From this base you can work out a plank distance, plank time , be it that photon light is travelling a distance at the speed of light,

 

Mike

Edited December 24, 2013 by Mike Smith Cosmos

[Viviator]

When photon is colliding with charged particle, it's absorbed, and later emitted.

Collision can be elastic, which means that newly created photon has exactly the same energy/frequency/wavelength as original.

Or inelastic, new photon has (usually) less energy, and charged particle is accelerated.

Emission of photon takes time. This feature is used by atomic clocks.

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

Thanks for replying. I considered absorption for this, and it makes a lot of sense, but I thought that reflection without absorption would also be possible in theory? But I guess then, that this is not the case? So just to see if I understand, suppose you have 2 nearly identical mirrors, where one is thinner then the other. (And they are both just a few atoms thick) the thicker mirror would reflect more of the light? Since some light might pass through the mirror not getting absorbed, and thus not reflected.

 

It might be confusing because that's not what quantum mechanics is saying. Planck units tell you where quantum gravity would be necessary vs general relativity. Not that these are the discrete values that are limits of resolution. Looking at the Planck energy should show you that.

Could you please elaborate on this? What do you mean when you say necessary? As in, we use one theory over the other at certain scales because that helps us explain what is going on, or a more fundamental change in what is going on at different scales. I've read up on planck energy, and I can understand how this couples in with general relativity, however, I still not understand how this would explain planck time as being something different from what I've described.

 

Also, if quantum mechanics is saying something different about planck units, then why do I so often see this explanation?

 

For example, this comes straight from wikipedia:

One Planck time is the time it would take a photon traveling at the speed of light to cross a distance equal to one Planck length. Theoretically, this is the smallest time measurement that will ever be possible,^[3] roughly 10⁻⁴³ seconds. Within the framework of the laws of physics as we understand them today, for times less than one Planck time apart, we can neither measure nor detect any change.

 

I'm I missing some subtleties? Or is this view simply wrong?

 

Just trying to understand. Thanks for the reply.

 

[swansont]

Necessary as in GR stops working, much like classical mechanics fails and special relativity is necessary. It does not imply that these units are quanta, just as picking a speed where SR is necessary does not imply that speed is quantized.

 

Smallest we could measure does not imply quanta, either. The caveat there is physics we understand today - we don't have a quantum theory of gravity, so any interpretation that requires one is speculative at best.

[DParlevliet]

I think that wikipedia is not saying that time is quantized, but that you can only measure it quantized.

[Viviator]

Necessary as in GR stops working, much like classical mechanics fails and special relativity is necessary. It does not imply that these units are quanta, just as picking a speed where SR is necessary does not imply that speed is quantized.

 

Smallest we could measure does not imply quanta, either. The caveat there is physics we understand today - we don't have a quantum theory of gravity, so any interpretation that requires one is speculative at best.

 

So, it's basically more a limit to our understanding of the world, rather than an actual physical limit? Is that correct?

I think that wikipedia is not saying that time is quantized, but that you can only measure it quantized.

This again would only make a difference if the unmeasurabillity of time is the result of our lack of knowledge/technology opposed to the physical nature of time just being unmeasurable at that scale. (that's how I previously understood it, that no single measurement of timespans smaller than planck time could have any meaning, regardless of the accuracy of measuring equipment etc.) So, do you also say that it's just a gap of our working knowledge and understanding pf physics?

 

Thanks

Edited December 24, 2013 by Viviator

[DParlevliet]

So, do you also say that it's just a gap of our working knowledge and understanding pf physics?

It is a part of physics, but we don't know why.

According Brian Greene it is not yet decided if time is continuous or quantized. But at Planck lengths all is so chaotic, that the meaning of before and after becomes meaningless.

Anyway I don't think it does influence "change" if time is seen as infinite small (when continuous) or in steps

[MigL]

What Greene is alluding to is a family of theories known as Loop Quantum Gravity where space-time ( not just time ) is a quantized field with no background 'stage' upon which events are located. This idea is respectful of General Relativity.

[timo]

It might be confusing because that [the Planck time and Planck length being the (smallest) unit of time or space, respectively] is not what quantum mechanics is saying.

Had the spontaneous urge to quote that.

[Viviator]

Had the spontaneous urge to quote that.

Okay, so I get that I misunderstood the meaning of the planck units. But then, what is quantum mechanics saying?

[Mike Smith Cosmos]

Surely the root quantity is energy, not time or distance but energy . Only integer (1,2,3,4....) chunks of energy are allowed, namely 1 x 6. Bla de bla x 10 to minus 34 joules. All this surely because there is frequency associated with each energy level change , the frequency of the photon released. And frequency waves only come in whole ,complete waves( 1,2,3,4,....)

 

Similarly the electrons, although nowerdays are considered in energy bands , were considered originally by Bohr , as existing as whole waves of tracks around complete orbits. Which do work out mathematically.

 

So the quantum effect as far as I understand it, originates here. I am sure someone will correct me if I am wrong in the way I have described it.

 

Now the word quantum seems to be applied to all things small. True all what I have said involves things like electrons, orbitals atoms and photons are all micro in size. But the word quantum really is to do with the chunks of energy.

 

Mike

[Kramer]

 

Dparlevliet say:
Anyway I don't think it does influence "change" if time is seen as “infinite small” (when continuous or “in steps”

A lay man say: Here are two thing for dispute: “ infinite” small”, and “in steps”.
Both are “speculation” and in contradiction with basement of law of physics. And both are the assets of Quantum mechanic theory in Copenhagen interpretation of physic’s phenomena.
It does influence a lot !

Timo say:
swansont say:, on 23 Dec 2013 - 9:35 PM, said:

------It might be confusing because that [the Planck time and Planck length being the (smallest) unit of time or space, respectively] is not what quantum mechanics is saying.

-----Had the spontaneous urge to quote that.
------ The lay man say: Why “spontaneous” urge and not “ premeditated “ and “well based”?

[DParlevliet]

....

 

And that is how a lay man debates and read posts.

[Sensei]

Okay, so I get that I misunderstood the meaning of the planck units. But then, what is quantum mechanics saying?

 

This subject was discussed in thread

http://www.scienceforums.net/topic/78975-plancks-electric-charge-factual-one/

See especially the end conclusions after #35 post..

[swansont]

Surely the root quantity is energy, not time or distance but energy . Only integer (1,2,3,4....) chunks of energy are allowed, namely 1 x 6. Bla de bla x 10 to minus 34 joules. All this surely because there is frequency associated with each energy level change , the frequency of the photon released. And frequency waves only come in whole ,complete waves( 1,2,3,4,....)

Planck's constant does not have units of energy, it has units of angular momentum.