This also describes very accurately the current state of some submitted papers of mine, lost in cold vacuum.

At least we now have some idea about the source of some of R. Munroe’s ideas.

There was a point in your writing that I personally didn’t like: the way you refered to the knowledge in the past. You used the notion of right/wrong. I would prefer Martin Hiedegger’s judgement about the knowledge in the past/present or future: transcending this or that kind of understanding.

I have seen a lot of polymaths pop up in recent days

Your query about the connection between invariance under translation and conservation of momentum (which is a very well-known consequence of Noether’s theorem. I point to the “fount of all wisdom” (just a joke): http://en.wikipedia.org/wiki/Noether%27s_theorem ) reminds me of a question I had for Richard Feynman decades ago:

I pointed out that, due to conservation of Momentum, it is not possible for a flexible body to change its position when constrained to the same shape. (In other words, the center of mass can’t change; so even if the body disassembles itself and then reassembles itself in the same way, the geometric center will be in the same place as before. It cannot change its “absolute position” with respect to the fixed stars.)

However, even though Angular Momentum is also conserved, it IS possible to change the orientation of a flexible body. (In other words: It CAN go through contortions and change its “absolute orientation” with respect to the fixed stars. This is how cats can be tossed, upside down, off a roof and still land on their feet (I am told).)

So there appears to be a significant difference between invariance under translation and invariance under rotation: Both imply conservation principles, but they don’t imply equivalent constraints with respect to “the fixed stars”.

Feynman appreciated the distinction, but didn’t have an explanation.

Denying the validity of the experience of time and the distinctions among past, present and future, one famous physicist (I don’t remember who) once wrote, “The universe does not BECOME, it simply IS.”

Thank you Sean! I look forward to your book

Using p for the momentum mv is relatively modern. I have some old physics textbooks (old meaning from the 19th century) and it is not used there. It appeared to work its way down from research into graduate texts and finally into undergrad texts by the mid 20th century.

p is used because the word “impetus” formally in place of “momentum” comes from the latin, “petere,” to go towards or rush upon…so therefore we get “p”
another way to look at it is q is used for the reaction and p is the mirror image of q so therefore since “to every action, there is an equal and opposite reaction,” we choose p to go with q

The most important question about momentum: why is it described by the letter “p”. I can understand why “m” would be confusing (unless you use weight), but why “p”?

Good question. My best guess is that it grew out of an analogy with pressure. (Does summing the momemta of individual particles give you an estimate of the pressure of an ideal gas? Off the top of my head I can’t say.) I attempted some basic research into the question just now, but came up empty-handed. All of my best books are currently in storage.

I don’t really want to argue about Wikipedia. It’s just a blog post, not an academic article. If something in the post is demonstrably incorrect, I’d be happy to change it.

Besides, you can always check the reference on Wikipedia if you are sceptical! At least tell us why it’s not Ibn Sina.

Because the concept of momentum was not really all that well defined until quite recently, and indeed continues to change.

What is momentum? J Roche 2006 Eur. J. Phys. 27 1019-1036

The author does not even mention Sina, but throws out quite a few other names? So who’s right? Once again, whoever controls the Wikipedia page. The Wikipedia page where the post author got the information from during a “wiki-trip”. He even links to that same page.

That paper was written in 2006? What will the same paper written in 2010 look like? If so, why? Wikipedia has profound effects on academia whether you like it or not. The only trouble is, academias effects on Wikipedia have been quite minimal and are in decline daily.

It’s not even likely the source.

The link is for us, not an academic reference.

Besides, you can always check the reference on Wikipedia if you are sceptical! At least tell us why it’s not Ibn Sina.