Can the presence of a field be detected w/o any charge?

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Discussion Overview

The discussion centers on the detection of electromagnetic fields, specifically whether it is possible to detect the Earth's magnetic field or an electric field without the presence of charged particles. Participants explore various methods and theoretical implications related to this topic.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants argue that detection of an electromagnetic field requires interaction with charged particles, suggesting that without them, detection is not feasible.
  • Others propose that very intense fields could lead to pair production, which is detectable, although the produced particles are charged.
  • There is a discussion about using methods such as the Hall effect or rotating coils to detect magnetic fields, which involve charged particles in their operation.
  • Some participants mention the Schwinger mechanism and its relation to pair production in high-energy collisions, noting that evidence for this effect is still lacking.
  • One participant suggests that one could infer the presence of a field based on the position of a charge, though this implies prior changes in the system.
  • There is a mention of the gravitational effects of electromagnetic fields, but participants note that these effects are too small to be detectable.
  • Another participant discusses the measurable contributions of electric fields to atomic mass measurements, indicating a potential form of detection, albeit indirectly.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether electromagnetic fields can be detected without charged particles. Multiple competing views and methods are presented, and the discussion remains unresolved.

Contextual Notes

Some claims depend on specific conditions, such as the intensity of fields or the methods of detection used. The discussion also highlights the limitations of current experimental evidence regarding certain theoretical effects.

sasan
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Is there anyway to detect the Earth's magnetic field without a compass? or putting it differently,
Is there anyway to detect an electric field without bringing a charged particle in proximity of the field?
 
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Hi sasan, :welcome:

To detect the presence of an electromagnetic field, you need something that interacts with that field. So: no. Only particles with charge can show some interaction.
 
Very intense fields can lead to pair production, that would be detectable - but the produced particles are charged, of course. It just means you don't need your own particles.
 
Note that your second question is not equivalent ('putting it differently' is an unfortunate wording) to the first: A compass is a permanent magnet, you could also use the Hall effect or a rotating coil to detect the Earth magnetic field.
 
mfb said:
Very intense fields can lead to pair production, that would be detectable - but the produced particles are charged, of course. It just means you don't need your own particles.
Well, if only we had these very intense fields at hand. There's yet no observation of this socalled Schwinger mechanism :-(.
 
vanhees71 said:
Well, if only we had these very intense fields at hand. There's yet no observation of this socalled Schwinger mechanism :-(.
Not yet, but the lasers are making progress towards it.
Pair production at ultraperipheral lead-lead collision is a related effect.
 
Hey guys, we had a simple question in this thread o_O
 
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Wow, this was my first post and I did get my question answered. I am so thankful. I truly am deeply thankful.
 
mfb said:
Not yet, but the lasers are making progress towards it.
Pair production at ultraperipheral lead-lead collision is a related effect.
Yes! This has a long history in heavy-ion collisions. As far as I know, so far there's also no (clear) evidence for the Schwinger effect there either. It's already tough to get the "normal dileptons" (which are very interesting in themselves, because they provide the most direct probe for in-medium effects of hadrons in the fireball created in heavy-ion collisions).

To get the Schwinger mechanism you need indeed ultra-peripheral collisions to avoid the creation of all this (from the point of view of the Schwinger pairs "background"). On the other hand you need the very large fields, which you may reach formally in such "grazing collisions", however for a very short time only.

The same holds for the large magnetic fields from the spectators in non-peripheral collisions and their impact on the heavy-ion observables in connection with the socalled "chiral magnetic effect".
 
  • #10
You can always observe a charge that's in a position when you expected to be in another position. Without seeing any actual change taking place, you can 'infer' that there must be a field there.(Same as a stretched spring could imply that it has a mass hanging on it or that a gravitational field is present.) But of course, that implies there was a change at some time in the past, when the present situation was set up.
 
  • #11
BvU said:
Note that your second question is not equivalent ('putting it differently' is an unfortunate wording) to the first: A compass is a permanent magnet, you could also use the Hall effect or a rotating coil to detect the Earth magnetic field.
But magnetic detectors such as these contain charges.
 
  • #12
In principle, the energy density of an EM field gravitates just like any form of mass/energy, I guess, but the effect is way too small to be detectable.
 
  • #13
hilbert2 said:
In principle, the energy density of an EM field gravitates just like any form of mass/energy, I guess, but the effect is way too small to be detectable.
Depends on what we count as detection. The mass of a singly ionized helium atom, the mass of an electron, and the mass of doubly ionized helium can all be measured to better than 10 eV. The first one is the sum of the other two minus 54 eV (the second ionization energy of helium). A +54 eV contribution from kinetic energy and a -109 eV contribution from the electric field. That contribution is measurable.
 

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