Descartes and I



I made a similar argument as a comment on Scott's blog. Surprisingly, not everybody believed it 8-).
But I think my responses were not that bad [1, 2, 3].
The following is a summary, in case you do not want to click through those comments:

I cannot doubt that I am, however I can doubt that my brain (or any other computational device) exists.
It follows that I cannot be my brain.

Descartes’ argument is really just two statements:
1) There is a function D(x) equal to my doubt about x. Let’s say D=0 means I cannot doubt x and D>0 means I can have doubts or actually have doubts.
2) from D(I) =/= D(B) it follows that I =/= B.

There is an important issue with 1), because my doubts D(x), in general, change over time. However, Descartes’ argument is that such a change in doubt is not possible for I and B: I cannot doubt that I am, but there will always be some doubt about B.

But let us assume you can convince me that I = B, in other words I am my brain. Now let me imagine a hypothetical supercomputer S in the future, which is capable of simulating human brains and in particular exactly emulates my brain B.
Will you also try to convince me that I = S , although it is clear that B is not S?

Notice that this hypothetical supercomputer S is constructed so that every argument b1, b2, … in favor of I = B has an equivalent argument s1, s2, … in favor of I = S.
The only way to avoid a contradiction (I=B and I=S but B is not S) is to argue that S does not really exist, it is only imagined.
But this is exactly Descartes' argument: We reject I = S because we have doubts that S may exist.


added later: After some more back and forth I summarized my argument in this final comment.

asymptotic safety not so safe?

A bit more than a week ago, Ethan wrote a pop. sci. piece about quantum gravity and explained why he thinks the asymptotic safety scenario is more convincing to him than string theory.
Obviously, Lubos had to respond in his trademark style, but he also linked to an old blog post of Jacques, who argued in 2008 that "the first nontrivial test of the asymptotic safety proposal" has yet to be calculated.

I used this opportunity to post a comment there to ask if somebody had performed this non-trivial calculation by now, seven years later (*). Jacques actually responded that "the situation looks considerably worse to me than it did at the time"; the reason being that all of those calculations break BRST invariance. (I recommend to push the 'view chronologically' button if you want to read the latest comments.)

I wonder what is going on in theoretical physics nowadays - is this just another breakdown of the peer review system or something worse?
I assume Reuter et al. have their arguments to pursue a line of research which Jacques et al. thinks is "completely unreliable". But it seems the field is falling apart into different tribes, strings, a.s., lqg, cdt, etc., who no longer discuss and argue with each other and gave up on the basic notion of right vs wrong some time ago.

I think if this continues for another seven years it can only get worse and to me this is all very sad.


(*) As far as I am aware the answer is no.


added later: Jacques wrote a new blog post about his problems with asymptotic safety for quantum gravity.

added much later: I wrote another short entry about this a while later.