# The Naked Scientists Forum

### Author Topic: Does a field have infinite extent?  (Read 5134 times)

#### jeffreyH

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##### Does a field have infinite extent?
« on: 07/12/2014 04:15:22 »
At some point between the source of a field and infinity the energy has to fall below a Planck limit where it will no longer be effective during interactions. The inverse square character of some fields can mean there is a range limit imposed on these fields. I may be very wrong on this point. Am I?

#### lightarrow

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##### Re: Does a field have infinite extent?
« Reply #1 on: 07/12/2014 19:33:05 »
At some point between the source of a field and infinity the energy has to fall below a Planck limit where it will no longer be effective during interactions. The inverse square character of some fields can mean there is a range limit imposed on these fields. I may be very wrong on this point. Am I?
If I've understood what you mean, then you should talk of energy density, not energy.
Anyway remember that classics electrodynamics has its limits and quantum electrodynamics instead come into play at low energy densities.

--
lightarrow

#### jeffreyH

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##### Re: Does a field have infinite extent?
« Reply #2 on: 07/12/2014 21:39:00 »
At some point between the source of a field and infinity the energy has to fall below a Planck limit where it will no longer be effective during interactions. The inverse square character of some fields can mean there is a range limit imposed on these fields. I may be very wrong on this point. Am I?
If I've understood what you mean, then you should talk of energy density, not energy.
Anyway remember that classics electrodynamics has its limits and quantum electrodynamics instead come into play at low energy densities.

--
lightarrow

Density is not quite the correct term. If a field has force carriers we can have particle density. The field itself may or may not have energy. Define a field. It is the effectiveness of the force implicit within the field. Imagine a tug of war between two men of equal height and weight and then replace one of the men by a large dog. Each pulling in opposite directions. Then replace the dog with a cat, then a mouse, then an ant, then a single-celled organism. How small do we go before the reduction in force becomes ineffective? Surely we reach this point before we reach infinity? If we can quantize space and time then can we quantize force? So is there a Planck force?

#### PmbPhy

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##### Re: Does a field have infinite extent?
« Reply #3 on: 07/12/2014 22:02:06 »
Quote from: jeffreyH
At some point between the source of a field and infinity the energy has to fall below a Planck limit where it will no longer be effective during interactions.
I don't know what you mean by a Planck limit so can you please explain what you mean by this in this context please?

Quote from: jeffreyH
The inverse square character of some fields can mean there is a range limit imposed on these fields.
Why do you think this is the case?

Quote from: jeffreyH
I may be very wrong on this point. Am I?
It's my understanding that the electric field, for example, is mediated by virtual photons. Thus the further apart the charges are the less photons per unit volume there are. However this also means that this has no limit and thus the field extends to infinity.

#### jeffreyH

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##### Re: Does a field have infinite extent?
« Reply #4 on: 07/12/2014 22:46:52 »
Yes I understand about the virtual photons. Within the future light cone there will be a drop in density. However uncertainty also comes into play. We could effectively end up with a force that can only move something 1 billionth or 1 trillionth of a Planck length per second. That surely will be ineffective and so can be ignored. This situation will occur before infinity as infinity is never reached.

#### Ethos_

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##### Re: Does a field have infinite extent?
« Reply #5 on: 08/12/2014 00:07:20 »
Yes I understand about the virtual photons. Within the future light cone there will be a drop in density. However uncertainty also comes into play. We could effectively end up with a force that can only move something 1 billionth or 1 trillionth of a Planck length per second. That surely will be ineffective and so can be ignored. This situation will occur before infinity as infinity is never reached.
Within the future light cone, one would assume at least one photon would exercise it's influence because it was squarely inline with the emission source. However with continual separation, I suppose the last effective point of influence would occur because that last photon was not perfectly aligned. So that last point of force would necessarily be from a single photon. And I'm sure we would all agree that this last point of applied force would occur long before infinity was reached. Whether one chooses to classify that force from a single photon as ineffective or not is up to the individual. Depends upon how much one wants to nit-pick.

But the forgoing conclusion would only account for the photon when understood as a particle. And would not hold true if we were talking about a wave. Because the photon can represent itself as either, depending upon the environmental circumstances, one might assume that wave would extend to infinity and still carry the force of a single photon with it.

Just thinking aloud......................
« Last Edit: 08/12/2014 00:21:03 by Ethos_ »

#### jeffreyH

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##### Re: Does a field have infinite extent?
« Reply #6 on: 08/12/2014 01:12:05 »
Some good points.

#### Ethos_

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##### Re: Does a field have infinite extent?
« Reply #7 on: 08/12/2014 02:44:20 »
Some good points.
Thanks Jeff and,.............. I would like to add, you ask some very intelligent questions.

#### PmbPhy

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##### Re: Does a field have infinite extent?
« Reply #8 on: 08/12/2014 06:55:09 »
Quote from: Ethos_
Thanks Jeff and,.............. I would like to add, you ask some very intelligent questions.
[/quote]
I strongly agree with Ethos_ on this point. Jeff, when you first arrived here your knowledge of physics was then nowhere as near to what it was now. When you first arrived here you had a great attitude, some spunk, solid honesty and willingness to learn, and learn you sure did! Your knowledge has increased dramatically since you arrived here and I'm proud to consider you my friend and I hope you think of me as a friend too! :)

You have a wonderful wiliness to learn both physics and a some of the philosophy of physics. How much your interest in the philosophy of physics is something I'm not sure of. But you're like me, i.e. you have a wonderful "thirst
" to learn.

If you enjoy the philosophy of physics then I recommend picking up the following books:

The Logic of Scientific Discovery by Karl Popper, Routledge Classics, (2002)
The Structure of Scientific Revolutions by Thomas S. Kuhn, The University of Chicago Press, (2012)
The Structure of Science: Problems in the Logic of Scientific Explanation by Ernest Nagel, Harcourt, Brace & World, Inc., (1961)

Jeff, may I ask how much you're interested in the philosophy of physics is?

#### alancalverd

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##### Re: Does a field have infinite extent?
« Reply #9 on: 08/12/2014 07:27:29 »
Classically, the field is infinite and its effect is infintesimal at large distances.

A quantum interpretation is that the probability of interaction between the source and the test particle decreases with 1/r^2 and is therefore never zero.

#### lightarrow

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##### Re: Does a field have infinite extent?
« Reply #10 on: 08/12/2014 11:41:09 »
At some point between the source of a field and infinity the energy has to fall below a Planck limit where it will no longer be effective during interactions. The inverse square character of some fields can mean there is a range limit imposed on these fields. I may be very wrong on this point. Am I?
If I've understood what you mean, then you should talk of energy density, not energy.
Anyway remember that classics electrodynamics has its limits and quantum electrodynamics instead come into play at low energy densities.

--
lightarrow
Density is not quite the correct term.
Then your statement is meaningless. Write the energy of a field, for example of the electromagnetic field.

--
lightarrow
« Last Edit: 09/12/2014 13:10:39 by lightarrow »

#### PmbPhy

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##### Re: Does a field have infinite extent?
« Reply #11 on: 08/12/2014 14:33:03 »
Yes I understand about the virtual photons. Within the future light cone there will be a drop in density. However uncertainty also comes into play. We could effectively end up with a force that can only move something 1 billionth or 1 trillionth of a Planck length per second. That surely will be ineffective and so can be ignored. This situation will occur before infinity as infinity is never reached.
Jeff - You never answered my question, i.e. I don't know what you mean by a "Planck limit" so can you please explain what you mean by this in this context please?  I have a feeling that you're talking about spatial distances where space gets foamy. If that's correct then it doesn't apply to this question.

#### jeffreyH

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##### Re: Does a field have infinite extent?
« Reply #12 on: 09/12/2014 02:34:14 »
Yes I understand about the virtual photons. Within the future light cone there will be a drop in density. However uncertainty also comes into play. We could effectively end up with a force that can only move something 1 billionth or 1 trillionth of a Planck length per second. That surely will be ineffective and so can be ignored. This situation will occur before infinity as infinity is never reached.

Jeff - You never answered my question, i.e. I don't know what you mean by a "Planck limit" so can you please explain what you mean by this in this context please?  I have a feeling that you're talking about spatial distances where space gets foamy. If that's correct then it doesn't apply to this question.

That is what I meant but I have modified my opinion. I'm almost finished Lee Smolin's book which was very informative although it is 12 years old now. I have a much better understanding of string theory, quantum loop gravity and the holographic principle. You should read it. There is sparse mathematics in it but the principles are put across well.
« Last Edit: 09/12/2014 02:36:57 by jeffreyH »

#### PmbPhy

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##### Re: Does a field have infinite extent?
« Reply #13 on: 09/12/2014 04:12:19 »
Quote from: jeffreyH
That is what I meant but I have modified my opinion. I'm almost finished Lee Smolin's book which was very informative although it is 12 years old now. I have a much better understanding of string theory, quantum loop gravity and the holographic principle. You should read it. There is sparse mathematics in it but the principles are put across well.
Thanks. Will do. When I get my new toner cartridge for my printer I'll print it out and start reading it.

#### jeffreyH

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##### Re: Does a field have infinite extent?
« Reply #14 on: 09/12/2014 23:23:23 »
Quote from: Ethos_
Thanks Jeff and,.............. I would like to add, you ask some very intelligent questions.
I strongly agree with Ethos_ on this point. Jeff, when you first arrived here your knowledge of physics was then nowhere as near to what it was now. When you first arrived here you had a great attitude, some spunk, solid honesty and willingness to learn, and learn you sure did! Your knowledge has increased dramatically since you arrived here and I'm proud to consider you my friend and I hope you think of me as a friend too! :)

You have a wonderful wiliness to learn both physics and a some of the philosophy of physics. How much your interest in the philosophy of physics is something I'm not sure of. But you're like me, i.e. you have a wonderful "thirst
" to learn.

If you enjoy the philosophy of physics then I recommend picking up the following books:

The Logic of Scientific Discovery by Karl Popper, Routledge Classics, (2002)
The Structure of Scientific Revolutions by Thomas S. Kuhn, The University of Chicago Press, (2012)
The Structure of Science: Problems in the Logic of Scientific Explanation by Ernest Nagel, Harcourt, Brace & World, Inc., (1961)

Jeff, may I ask how much you're interested in the philosophy of physics is?
[/quote]

I am interested in the philosophy, history and the biographies of the early pioneers. I have gone back as far as the histories of Tycho Brahe, Kepler and Newton. I have read the biography of Schrodinger and will try to read more on others in the future. You often have to review history to gain insight.

#### PmbPhy

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##### Re: Does a field have infinite extent?
« Reply #15 on: 10/12/2014 00:19:41 »
Quote from: jeffreyH
I am interested in the philosophy, history and the biographies of the early pioneers. I have gone back as far as the histories of Tycho Brahe, Kepler and Newton. I have read the biography of Schrodinger and will try to read more on others in the future. You often have to review history to gain insight.
I'm glad to hear that. You'll get a lot of history from the philosophy of physics. What books have you read/are you reading on the philosophy of physics?

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##### Re: Does a field have infinite extent?
« Reply #15 on: 10/12/2014 00:19:41 »