# Why are magnetic lines of force invisible?

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?

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Hi Suvankar. Welcome to Physics.SE. Shall I ask a question to you: "Then, Have you seen gravitational, electric and electromagnetic fields?" Please have a look at the wiki links. They may provide some intuitive look on the topic :-) – Waffle's Crazy Peanut Jan 18 '13 at 15:08
You can only see things if they generate, absorb, reflect, or refract light. BTW, you can see magnetic fields by using iron filings. – Mike Dunlavey Jan 18 '13 at 15:27
This is an interesting question. Too bad it was never answered. Some species of birds can see magnetic fields, after all. – markovchain Mar 30 '13 at 4:26
@markovchain Yes, the bird is interesting. I've answered it, what do you think? – Volker Siegel May 1 '14 at 4:44

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.

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Yes, I wrote about that - "feeling the direction" of the field of Earth is useful. But it is not a reason to "see" field lines in any spatial resolution. – Volker Siegel May 1 '14 at 4:55
Oh, now I see. Hmm, how is it possible to see (the value of) a field at a remote location? I'd think the best an animal could do is communicate the value at its own position to others of the species. – Blackbody Blacklight May 1 '14 at 4:59
Hmm... not sure how it would work out for magnetic fields, will not look like a drawing in a physics text book for sure. Maybe comparable to how we perceive sound? Good question! – Volker Siegel May 1 '14 at 5:04
The point is, you can't see any remote field. You can only decode sound and light waves that hit your ears and eyes. – Blackbody Blacklight May 1 '14 at 5:29
@BlackbodyBlacklight I think birds, for example , feel the orientation of the field lines. Going in parallel or crossing them will make a difference to the small electric currents in their brain. en.wikipedia.org/wiki/Magnetoception – anna v May 1 '14 at 5:30