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22 June 2013 - 11:57 AM
QuoteThe easy way would be to find a closed curve around which the integral of Fdx would be zero, but since Fdx is a 1-dimensional 1-form, this doesn't seem to be a meaningful way to do it.
Non-zero. For a non-conservative force, the integral would be non-zero.
In general, you are overthinking this. Take a step back- can you find two paths along which a different amount of work is done? What happens if I travel slowly from x = 0, t = 0 to x = x_1, t = t_1. Now, what happens if I travel quickly to arrive at x_1, and then simply wait until t = t_1. Does the force do different amounts of work? Is the work path independent?
23 December 2012 - 09:51 PMwhy hasn't one been observed? Is it because gravity is a psuedoforce... one that is not a true physical force and therefore does not have a mediator?
The very theory that predicts the graviton predicts that its coupling is INCREDIBLY weak. We simply have no data where we expect to see gravitons. Hell, we have no direct data where we observe gravitational waves, which are easier to observe by a factor of hbar.
23 December 2012 - 05:14 PMI'd say- funding. The lack of growth in scientific funding, and the resulting pyramidal structure in the scientific workforce (something like 7/10 physics phds are forced out of 'STEM' all together within 5 years of getting a phd) makes pursuing hard problems a career killer. The average phd time is up above 6 years, and then the average time from postdoc to faculty position is right at 6 years. During this time career uncertainty is huge- without a steady stream of published results you will lose your job.
So we take physicists during their most creative years and 1. tie their funding to a different investigator (during your postdoc you don't do YOUR research,you do the project of whoever hired you). 2. force them to focus on short term vs. long term projects, and 3. pay them about as much as a manager of a mid-sized fast food restaurant (but with less job security)- this last one dramatically increases overall stress level.
Its not a surprise we don't make much progress- its a surprise we make any at all. Incentives matter- and the scientific labor market seems crafted to push talent away from the field, rather to draw it in and retain it.
20 December 2012 - 07:46 PMIf a sufficiently large and powerful but otherwise ordinary computer can realistically simulate a portion of something like our universe, I’ve a poorly defined suspicion that, on the scale at which quantum effects are detectable, it couldn’t work, because the rewind/replay/inspect nature of a simulation would violate quantum mechanical principles such as uncertainty. If (and this is a big if, in which I don’t personally believe) consciousness theorists like the New Mysterians are correct in their belief that brains can’t function without exploiting key quantum effects – in other words, that the human brain can’t be simulated with an ordinary computer, ancestor simulations just aren’t possible.
It depends on what you mean by simulation. I'd suggest something like an emulated person is a type of simulation, even if the rewind,replay, inspect properties can't exist.
QuoteWhile it’s waiting for potentially dangerous AIs to defang, SIAI strikes me as more of a conversation salon than a serious AI research institute. It brings together some thought-provoking ideas and people, though, so I like it.
My largest problem is that (before I'd even heard of the institute), I had a student who had learned some rather strange notions of both statistics and physics from some singularity institute literature. Its very hard to get someone pre-committed to wrong ideas to unlearn them!
When I dove into looking at the singularity institute, they struck me as being a lot like the cryonicists, Drexler, etc. They strike me as dilettantes- dabbling in hard problems but unwilling to do the hardwork of coming to terms with the scientific state-of-the-art so they can make real contributions. Instead, they bandy about wild-ideas and argue about meta-issues. I guess everyone needs a hobby, but these guys fund-raise and set-up as non-for-profits (and in the case of the cryonics guys offer a paid service that clearly doesn't work). I'm willing to bet many of their small donors lack the relevant expertise to separate them from real scientists. The only difference between them and con-artists is their fervent belief.
When last I checked, after a decade and hundreds of thousands of dollars, the singularity institute had produced only a few self-published non peer-reviewed papers, a lot of blog entries, and ~1/3 of a rather long Harry Potter fan story.
QuoteAs a group, they seem to me pathologically unwilling to consider the most critical problems with their dream of a general purpose molecular assembler, contributing to a profound schism between by twin loves of science fiction and scientific reality.
I'd agree and argue a similar problem plagues the singularity institute and probably most self-described "trans-humanist" groups.
QuoteAssuming that such simulations (that is, running a universe on a computer, rather than creating a real universe and watching it run) are possible, its users likely wouldn’t need to wait longer than they wanted for results, because just as with present-day physics simulations (eg: simulation of the formation of the solar system), there’s no requirement that simulation time progress at the same rate as real time. So our far-future simulation programmers might run a 4-billion year-long simulation of the appearance and evolution of life on Earth on a super-fast computer that would complete the run in seconds or minutes of real time – handy, if you’re trying to tweak initial conditions to produce some desired end result.
If these sorts of simulations aren’t possible for our imagined future folk, but engineering on planetary scales is, terraforming a real planet and running essentially a giant petri dish experiment might be the only way to go – but, coupled as experiments are to real time, the folk running them would have to be awfully patient....
Our super-engineering-enable biologists might need not just to build planets to order, but stars as well. It’s only my gut-instinct, by programming computers to simulate biospheres in much-faster-than-realtime seems an easier, less mind-boggling approach to me.
I guess I'm sort of operating on the premise that the universe is really big. Building insanely powerful, insanely energy hungry computers to run simulations might just be orders of magnitude more costly than finding N planets that fit what you want, dropping some life on them, and returning to visit every few hundred years. Assuming arbitrarily long-lived super-people, I can see that they might take the much cheaper option (this assumes interstellar travel is cheaper than mega-computers that can simulate planets). You might not be able to do a ton of experiments end-to-end, but tons of parallel runs are possible.
I think the only life-form we've successfully simulated (and not in full detail!) is the tobacco mosaic virus, which took weeks of super-computer time and was simulated for only about 50ns. Even assuming orders of magnitude more power, simulating whole civilizations is likely to be prohibitively expensive.
That said, my officemate in graduate school used to say that things like an arbitrary max. speed and a limited distance/momentum resolution were just the sort of shortcuts he'd put in a simulation.
20 December 2012 - 12:32 AMI've never been impressed with Bostrom's work, although that might be colored by my hugely negative impression of groups like the singularity institute.
As far as the trilemma, I think there are other possibilities. It seems probably that the most resource efficient way to do an ancestor simulation is to seed a planet with some simple lifeforms and wait- i.e. experiments might be easier than simulations. After all whatever a "posthuman" civilization might be operating over very long time scales.
Perhaps there is an upper bound on calculation density- Moore's law flattens out before simulating an entire civilization becomes feasible (there are physical limits to information density, there may well be physical limits to calculation density),etc