[Physics] Why are magnetic lines of force invisible

electromagnetismmagnetic fields

We can very well feel the magnetic field around a magnet, but we can't see it. Why is that so?

Also, can we cut a portion of the field and use it?

Best Answer

Magnetic fields are not visible because it was not important during evolution to acquire that capability.

That makes sense when you look where to find magnetic fields in nature.

There is the field of Earth, that can be used for navigation. It is used by compasses, and also some animals and even bacteria which can somehow feel the field. But it makes no sense to see it - it would look the same, more or less, maybe with lines in some direction.

Other magnetic fields are only relevant in special locations, where certain metals are found in the ground etc. and pretty uncommon.

So, until we started to handle metal pieces, electricity, and magnets, there was no question "why is it invisible", but "why should it be visible".

We never had a reason to learn it during evolution, but I do think we could have learned to see magnetic fields in some way if it had been helpful.

On cutting a portion of a magnetic field:

To be exact, it's not that a magnet has a magnetic field, and another magnet has another field - there is only one magnetic field.
The field is not part of the magnet, it is only the description of all the magnetic field lines, that all influence each other.
So, there is only one magnetic field in this universe, and you need to make a hole into the universe to make a hole in the field.

Not sure a black hole would count.