The h Bar

Aaron Stevens

4:41 AM

@WhitePrime Do you mean cathedral of physicists?

DanielSank

6:55 AM

Hi, everybody.

user157860

7:12 AM

@JohnRennie, hi John, division by zero has been determined as infinity, zero and then undefined or an operation not permitted, right? But in real world, in physics a lot of formulae are a ratio, can you describe what actually happens to such phenomena/functions when the denominator goes to zero?

John Rennie

@user157860 division by zero is always undefined. In physics a division by zero never happens. If you find you have a division by zero this is a sign that whatever you are considering is unphysical.

user157860

@JohnRennie, that is really surprising! please clarify why denominators of formule can never go to zero.Thanks

John Rennie

@user157860 why is it surprising?

Actually I suppose we can have 0/0 in the sense of a limit of infinitesimals, but that isn't really dividing zero by zero.

You don't have a finite number divided by zero in physics because there are no infinities in physics.

user157860

@JohnRennie, as I mentioned, most basic formulae contain a division, so , I thought, for all or most of them there must be a case when that denominator goes to zero.

John Rennie

@user157860 but there is no physically realistic situation where that would happen.

user157860

7:25 AM

actually, 0/0 should be the real undefined one 0/0 = n, since any number multiplied by zero is 0 0=0n, don't you think?

@JohnRennie , alright, I 'll reflect on that and if I find one case I'll submit it to you.

John Rennie

Where this happens in physics it's usually the result of taking limits e.g. v = s/t in the limit where both s and t go to zero.

So even though we end up with 0/0 we approach the limit in such a way that the ratio is well defined.

user157860

@JohnRennie, I was rather thinking of denominators which contain a subtraction, that surely must have a realistic instance

John Rennie

@user157860 if you can think of one let me know :-)

user157860

@JohnRennie, OK thanks

John Rennie

@user157860 even some mathematicians argue that infinity doesn't exist, though this is a minority view.

user157860

7:35 AM

@JohnRennie, the concept of infinity in actu has caused a lot o fallacies in physics. When Cantor advanced the idea in 1875 he was jeered and defined insane, I still can't understand how mathmen and physicist could later accept that

John Rennie

I don't think Cantor was "defined insane" as you put it. He had very real problems and committed himself. I agree that his work wasn't viewed positively by the establishment.

I don't see any problem with defining infinities in mathematics because mathematics isn't physics.

user157860

@JohnRennie, if you don't stick to reality, you get into trouble. Probably one can fool around in maths, but when you import such nonsense as Infinity+1 = infinity into physics you surely derail

John Rennie

I suspect most physicists would agree that actual infinity does not exist in the real world.

user157860

8:03 AM

@JohnRennie, I am glad to hear that, but in a discussion we had a while ago you did not agree that the forces of an electron never go to infinity. I maintained that there is no singularity and that blackholes are full of mythology and that any force (gravity etc) is considered at the centre of the mass/particle ant that that is its max value. Can you remember?

John Rennie

@user157860 I don't remember that. Do you have a link?

user157860

@JohnRennie, no, it was long ago, but if you wish we can go back on that sometime

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