Field is something more than just a region

  • #1
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Main Question or Discussion Point

Hello,

I believe that a field is something more than just a region. I feel it has something that we all don’t know. If anyone knows more in this topic can they share it?

-Benzun
All For God
 
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Answers and Replies

  • #2
selfAdjoint
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A field in theory is defined to be a something (number, vector, etc.) which has a value at each point of space (or spacetime in relativistic theories). So it's just like a function, f(x,y,z) where the value of f could be a number or a vector or spinot or whatever.

Physically you go anywhere and measure the intensity of a field and you get an answer. At different points the intensity could be different. The temperature of the air is an example. If it's a vactor field, what you experience will be a force (like attraction near a magnet).

From the point of physics the most important additional property a field has is symmetry. The values of the of the field don't change if you change coordinates in various ways. This leads to physical laws.
 
  • #3
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benzun_1999,
I guess you refer to a definition that appears in some school textbooks. "The region where magnetic forces appear is called the magnetic field" or similar. I think this is a nonsensical, misleading statement.
selfAdjoint gave a correct definition.

And why is it, historically, called a 'field'?
Imagine you use a grid of points, and draw from each point a short arrow in the direction of the observed force, with a length proportional to the force's absolute.
You get a pattern much resembling a field of corn plants or so, which are being bent in different directions by the wind.
I guess that is why, historically, it has been called a 'field'.
 
  • #4
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thanks....but....need more help

Thank you for helping me, I feel that a magnetic field is a region where a special kind of wave travels. these waves are only created when an object is placed in it. These waves have alternating energy, frequency. the frequency keeps increasing.

-Benzun
 
  • #5
selfAdjoint
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Originally posted by benzun_1999
Thank you for helping me, I feel that a magnetic field is a region where a special kind of wave travels. these waves are only created when an object is placed in it. These waves have alternating energy, frequency. the frequency keeps increasing.

-Benzun
What physical phenomena can you cite for this description of the magnetic field? Why do you think there is a frequency and why do you think it is increasing?
 
  • #6
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Originally posted by benzun_1999
I feel that a magnetic field is a region where a special kind of wave travels.
I disagree. I say, you can have a field without a wave. Because, a wave is something that shows some change with time. But you can have fields that don't change with time (stationary fields). Take a magnet. Cover it with a sheet of paper, and scatter iron filings onto it. What you see, is a pattern of lines giving a rough representation of the magnetic field. No change with time, there. So, no wave.
these waves are only created when an object is placed in it.
Placed in what? I think you say "A field is something that creates waves when an object is placed in it". That, to me, is rather the definition of a medium, not a field. Water may create waves when something is thrown into it. Water is a medium, not a field.
These waves have alternating energy, frequency.
Careful. A wave can have a frequency, OK, but what do you mean by 'alternating energy'? Energy is a property of a physical system - what system are you talking about? 'Alternating' may mean, it changes sign as time proceeds - so 'alternating energy' would mean, positive now, and negative later, and zero in between. Are you sure you mean this?
the frequency keeps increasing.
It does if something oscillates faster and faster. But that has nothing to do with fields, does it?

Please excuse if I sound unfriendly - don't mean to. I'm not a native speaker. Just trying to be helpful.
 
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  • #7
bandonrun
I disagree. I say, you can have a field without a wave. Because, a wave is something that shows some change with time. But you can have fields that don't change with time (stationary fields). Take a magnet. Cover it with a sheet of paper, and scatter iron filings onto it. What you see, is a pattern of lines giving a rough representation of the magnetic field. No change with time, there. So, no wave.
What would you expect those iron filings to be doing if the field had waves? Jiggle?
I fail to see how this little experiment suggest that a magnetic field is not a wave, or has no waves.
 
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  • #8
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OK, bad example, maybe. I admit a field is a theoretical construct, so we can't prove or disprove any field properties by experiment. Still, you can define a stationary field - while a wave in my understanding is not stationary but time-dependent.

I guess benzun_1999 is wondering how a magnet or charge can influence a body at a distance, even thru a vacuum. I guess that's why he says 'a wave travels'. Sure it's mysterious how one body can affect another when there's 'nothing in between'.

I think we are takling about 2 different questions:

Question 1: How can we describe mathematically the influence of one body on another, distant body? Answer: By fields.

Question 2: Why does this influence occur? Well, there have been many answers to this: Faraday's mechanistic ideas, ether theories, modern gauge-invariance arguments, and so on. I just think 'a wave travels' is not a good answer, since there is no experimental evidence for this.
 
  • #9
selfAdjoint
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Or "a boson travels"? The boson being the quantum of the field.
 
  • #10
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thanks....but....need more help

i thank you for helping me to overcome the confusion i had i will be happy if someone tell me more about what is in the field ?
 
  • #11
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Does field have an end ?????????????[?]
 

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