What is a Physicist? A Mathematician? A Computer Scientist?
19 September 2018 | 12:16 am

 Scott Aaronson recently won the Tomassoni-Chisesi Prize in Physics (yeah Scott!).
In his post (here) about it he makes a passing comment:

I'm of course not a physicist

I won't disagree (does that mean I agree? Darn Logic!) but it raises the question of how we identify ourselves. How to answer the question:

Is X a Y?

(We will also consider why we care, if we do.)

Some criteria below. Note that I may say thinks like `Dijkstra is obviously a computer scientist'
but this is cheating since my point is that it may be hard to tell these things (though I think he is).

1) If X in a Y-dept then X is a Y. While often true, there are some problems: MIT CS is housed in Mathematics, some people change fields. Readers- if you know someone who is in dept X but really does Y, leave a comment. (CORRECTION- I really don't know how MIT is structured. I do know that the Math Dept has several people who I think of as Computer Scientists: Bonnie Burger,  Michael Goemans, Tom Leighton, Peter Shor, Michael Sipser. There may be others as well. The point being that I would not say `Sipers is a mathematician because he is in the MIT Math Dept')

2) If X got their degree in Y then they are Y. Again, people can change fields. Also, some of the older people in our field got degrees in Physics or Math since there was no CS (I am thinking Dijkstra-Physics, Knuth-Math). Even more recently there are cases. Andrew Child's degree is in Physics, but he did quantum computing. Readers- if you know someone who got there degree in X but is now donig Y, leave a comment.

3) Look at X's motivation. If Donald Knuth does hard math but he does it to better analyze algorithms, then he is a computer scientist. One problem -- some people don't know their own motivations, or it can be hard to tell. And people can get distracted into another field.

4) What does X call himself? Of course people can be wrong. The cranks he email me their proofs that R(5) is 40 (its not) think the are mathematicians. They are not- or are they? see next point

5) What X is interested in, ind. of if they are good at it or even know any. Not quite right- if an 8 year old  Bill Gasarch is interested in the Ketchup problem that does not make him a mathematician.

6) What X is working on right now. Fine but might change. And some work is hard to classify.

7) If you win an award in X, then you are an X. Some exceptions

Scott is a computer scientist who won the Tomassoni-Chisesi Physics Prize

Ed Witten is a Physicist who won the Fields Medal (Math)

John Nash is a mathematician who won a Nobel prize in Economics.

I want to make a full circle- so if you know other X won a prize in Y then leave a comment and
we'll see what kind of graph we get. Bipartite with people on one side and fields on the other.

8) What they can teach? Helpful in terms of hiring when you want to fill teaching needs.

Does any of this matter? We use terms like `mathematician' `physicist' `computer scientist' as shorthand for what someone is working on, so its good to know we have it right.

P = NP and Cancer
13 September 2018 | 12:08 pm

Often when the question comes to what happens if P = NP, one typically hears the response that it kills public-key cryptography. And it does. But that gives the impression that given the choice we would rather not have P = NP. Quite the opposite, P = NP would greatly benefit humanity from solving AI (by finding the smallest circuit consistent with the data) and curing cancer. I've said this before but never explained why.

Of course I don't have a mathematical proof that P = NP cures cancer. Nor would an efficient algorithm for SAT immediately give a cancer cure. But it could work as follows:
  1. We need an appropriately shaped protein that would inhibit the cancer cells for a specific individual without harming the healthy cells. P = NP would help find these shapes perhaps just the DNA of the person and the type of cancer.
  2. At this point we don't understand the process that takes a ACGT protein sequence and describes that shape that it forms. But it must be a simple process because it happens quickly. So we can use P = NP to find a small circuit that describes this process.
  3. Use P = NP to find the protein sequence that the circuit from #2 will output the shape from #1.
We'll need an truly efficient algorithm for NP problems for this to work. A n50 algorithm for SAT won't do the job. All this steps may happen whether or not P = NP but we'll need some new smart algorithmic ideas.

Please note this is just a thought exercise since I strongly believe that P ≠ NP. I do not want to give false hope to those with friends and loved ones with the disease. If you want to cure cancer your first step should not be "Prove P = NP". 

The Tenure system is broken but not in the way that you think (Anon Guest Post)
11 September 2018 | 5:48 pm

This is an ANON guest post. Even I don't know who it is! They emailed me asking if they
could post on this topic, I said I would need to see the post. I did and it was fine.

I have written many tenure/promotion letters before. But this summer, I was especially inundated with requests. Thinking about my past experiences with such letters, I started to question their value.

For those unfamiliar with the process, let me explain. When someone is applying for a research job, they typically need to have recommendation letters sent on their behalf. Once someone is hired in
a tenure-track position, they then need to get additional letters each time they are promoted (in the US, this will typically occur when someone is granted tenure and again when they are promoted to full

Now, I know from experience that recommendation letters are scrutinized very carefully, and often contain useful nuggets of information. I am not questioning the value of such letters (though
they may have other problems). I am focusing here only on tenure/promotion letters.

Let me fill in a bit more detail about the tenure/promotion process,since it was a mystery to me before I started an academic position. (I should note that everything I say here is based only on how things are
done at my institution; I expect it does not differ much at other US universities, but it may be different in other countries.) First, the department makes a decision as to whether to put forward someone's
case for promotion. If they do, then a package is prepared that includes, among other things, the external recommendation letters I am talking about. After reviewing the candidate's package, the department holds an official vote; if positive, then the package is reviewed and
voted on by higher levels of administration until it is approved by the president of the university.

The external letters appear very important, and they are certainly discussed when the department votes on the candidate's case. However, I am not aware of any cases (in computer science) where someone who was put forward for tenure was denied tenure. (In contrast, I am aware of a very small number cases where a department declined to put someone forward for tenure. In such cases, no letters are ever
requested.) Perhaps more frustrating, this seems to be the case even when there are negative letters. In fact, I have written what I consider to be "negative" letters in the past only to see the candidate still get tenure.(To be clear, by academic standards a negative letter does not mean saying anything bad, it just means not effusively praising the candidate.) This makes be believe that these letters are simply being used as "checkboxes" rather than real sources of information to take into account during the decision-making process. Essentially, once a department has decided to put someone forward for promotion, they have effectively also decided to vote in favor of their promotion.

Letters take a long time to write, especially tenure/promotion letters, and especially when you are not intimately familiar with someone's work (even if they are in the same field). But if they are
basically ignored, maybe we can all save ourselves some time and just write boilerplate letters (in favor of tenure) instead?

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