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Stabilizer comments on Welcome to Less Wrong! (2010-2011) - Less Wrong

42 Post author: orthonormal 12 August 2010 01:08AM

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Comment author: Stabilizer 14 December 2011 05:31:15AM *  23 points [-]

Hey everbody,

I'm a PhD Student in Physics. I came across Lesswrong when I read Eliezer's interview with John Baez. I was very intrigued by his answers: especially with his idea that the world needs to understand rationality. I identify with rationalism and especially with Lesswrong, because it just clicked. There were so many things in the world which people accepted and which I knew were just plain wrong. And before I found Lesswrong, I was a frustrated mess. And when I found Lesswrong it was a breath of fresh air.

For example: I was a pretty good debater in college. So in order to be a better debater, I started reading more about logical fallacies, which are common in argument and debate, such as ad hominem, slippery slope, appeal to authority etc . And the more I learnt about these, the more I saw that these were exactly the techniques common in debate. I was forced to conclude that debating was not about reaching the truth, but about proving the other person wrong. The people in debating circles were very intelligent; but very intelligent in a useless (and maybe harmful) way. They were scarcely interested in the truth. They could take any argument, twist it, contort it, appeal to emotions and use every fallacy listed in a beautiful way to win. And moreover, that was the exactly the kind of person I was becoming. In retrospect, it's clear to me that I got into debating only out of desire for status and not for any actual interest in the truth. But as soon as I saw what I was becoming, I walked away. I guess, the kernel of honesty left in me from being a student of physics rescued me in the end.

Second example: One of the first articles that really brought me into reading major portions of Lesswrong was the article on Doublethink by Eliezer. So when I was going through a phase of depression, I thought that religion held the key. Now, I did not believe in any kind of spiritual god or any spiritual structure whatsoever. But my family is extremely religious and I saw the happiness they got from religion. So I tried. I tried to convince myself that religion has a very important social function and saves people from anomie and depression. I tried to convince myself that one could be religious and yet not believe in god. I tried to go through all the motions of my religion. Result? Massive burnout. My brain was going to explode in a mass of self-contradiction. That post by Eliezer really helped me. There's a line in there:

The happiness of stupidity is closed to you. You will never have it short of actual brain damage, and maybe not even then... You cannot unsee what you see.

As I read these lines, I literally felt a huge wave of relief sweep over me. I wasn't going to be happy with religion. Period. I wasn't going to be happy with self-deception. Period. And I knew I had finally found people who 'got it'.

So that was a glimpse of how and why I got interested in Lesswrong. I'm reading the Sequences and looking around these days. I hope to start posting soon. And also attend LW meetups in my city.

I'm deeply interested in ideas from evolutionary psychology, neuroscience, computer science and of course physics! I work broadly on quantum information theory.

Cheers!

-Stabilizer

Comment author: Swimmer963 12 January 2012 04:27:24PM *  4 points [-]

Welcome, Stabilizer!

So I tried. I tried to convince myself that religion has a very important social function and saves people from anomie and depression. I tried to convince myself that one could be religious and yet not believe in god. I tried to go through all the motions of my religion. Result? Massive burnout. My brain was going to explode in a mass of self-contradiction.

Interesting that you say this...I haven't had the same experience at all. I was raised basically agnostic/atheist, by parents who weren't so much disapproving of religion as indifferent. I started going to church basically because I made friends with a girl who I had incredibly fun times hanging out with and who was also a passionate born-again Christian. I knew that most of the concepts expressed in her evangelical Christian sect were fallacious, but I met a lot of people whose belief had allowed them to overcome difficult situations and live much happier lives. Even if true belief wasn't an option for me, I could see the positive effect that my friend's church had, in general, in the community it served. And I was a happier, more positive, and more generous person while I attended the group. There was a price to pay: either I would profess my belief to the others and feel like I was lying to a part of myself, or I wouldn't, and feel like ever-so-slightly an outsider. But maybe because of my particular brain architecture, the pain of cognitive dissonance was far outweighed by the pleasure of having a ready-made community of kind, generous (if not scientific-minded) people eager to show me how welcoming and generous they could be. I have yet to find something that is as good for my mental health and emotional stability as attending church.

That being said, a year of not attending church and reading LessWrong regularly has honed my thinking to the point that I don't think I could sit back and enjoy those church services anymore. So that avenue is closed to me now, too.

Comment author: TheOtherDave 12 January 2012 05:28:04PM 3 points [-]

For what it's worth, it depends a lot on the church service: I know quite a few very sharp thinkers whose church membership is an important and valuable part of their lives in the way you describe. But they are uniformly members of churches that don't demand that members profess beliefs.

One gentleman in particular gave a lay sermon to his church on Darwin's birthday one year about how much more worthy of admiration a God who arranges the fundamental rules of the universe in such a way that intelligent life can emerge naturally out of their interaction, than is a God who instead must clumsily go in and manually construct intelligent life, and consequently how much more truly worshipful a view of life is the evolutionary biologist's than the creationist's, which was received reasonably positively.

So you might find that you can get what you want by just adding constraints to the kind of church service you're looking for.

Comment author: Swimmer963 15 January 2012 02:37:59PM 4 points [-]

I know quite a few very sharp thinkers whose church membership is an important and valuable part of their lives in the way you describe. But they are uniformly members of churches that don't demand that members profess beliefs.

Sounds like the Unitarian church that my parents took us to for a few years...I'm not sure why they took us, but I think it might have had more to do with "not depriving the children of a still-pretty-typical childhood experience like going to Sunday school" than with a wish to have church an important part of their lives.

I would probably enjoy the Unitarian community if I joined for long enough to really get to know them... I'm sure the adults were all very kind, welcoming people. Still, the two churches that I've attended the most are High Anglican and Pentecostal. The Anglican cathedral is where I sang in the choir for more than five years, and the music is what really drew me; although the Anglican church is very involved in community projects and volunteering, almost the whole congregation is above the age of fifty, and the young people who do attend are often cautious, conservative, and not especially curious about the world, which reduces the amount of fun I can have with them.

Surprisingly enough, in the Pentecostal church where the actual beliefs professed are much more extreme, most of the congregation are young and passionate about life and even intellectually curious. They are fun to hang out with...in fact, I frequently had more fun spending a Friday night at a Pentecostal event than at a party. They took their beliefs seriously and really lived according to how they saw the Bible, even though I have no doubt their actions would have been considered weird in a lot of contexts and by many of their friends. I think a lot of the apparent mental health benefit of this church came from the community's decision to stop caring about social stigmas and just live. This is, I think, what I most respected about them...but for a lot of the same reasons, I now find their ideas and beliefs a lot more jarring than those of the Anglican church.

I have no doubt that there are churches on all sides of the continuum: "traditional" communities, like the Anglican church, which are socially liberal and also composed of fun young people...and also fundamentalist evangelical churches which have ossified into organizations with strict rules and a lot more old people than young people. Maybe somewhere out there is a church that has all the aspects I like (singing, rituals, fun young people who do outrageous things together and bond over it) and is also bearable non-evangelical, non-fundamentalist, and socially liberal, but I haven't found it yet.

Comment author: Stabilizer 13 January 2012 02:51:55AM 0 points [-]

But maybe because of my particular brain architecture, the pain of cognitive dissonance was far outweighed by the pleasure of having a ready-made community.

I used to have that kind of brain architecture for quite some time, and I kind of miss it. But as I started studying more and more physics, it just became harder and harder. So, I guess the trade-off got really skewed at some point of time.

I have to mention that my religiosity kind of went through cycles. There was a time when I was an internally-militant (not very outspoken) atheist, followed by a period of considerable appreciation for religion, and again followed by a (currently) pretty comfortable atheism. If I think back to my first episode of atheism (religion was my default state as I was born in a pretty religious family), I guess I was pretty uncomfortable with it, in the sense that I felt that a lot more needed to be explained. In the intervening episode of religiosity, I appreciated the exact things that you mention about religion, but I just didn't like all the baggage, i.e. the time and money spent in rituals. My religion was Hinduism, which is highly ritualistic, but enjoys some nice philosophies. I still like some of the philosophy but I dislike most of the ritual.

Comment author: Swimmer963 15 January 2012 02:42:25PM 0 points [-]

I appreciated the exact things that you mention about religion, but I just didn't like all the baggage, i.e. the time and money spent in rituals.

Funny. That's probably a brain architecture thing, too, but I really enjoy a lot of the High Anglican rituals at the church where I used to sing in choir. The traditional carols that all of us know by heart, every single word... The ministers and the bishop in their beautiful robes leading the choir in a procession around the cathedral while we sing in insane harmony... Stuff like the ritual of turning out all the lights and everyone leaving in the dark on Maundy Thursday (day before Easter Friday) to symbolize Jesus' death. It's all very theatrical, and very moving, and usually makes me cry.

I have a feeling that you might be talking about a different kind of ritual, though, if you're frustrated by the amount of time and money spent on them.

Comment author: [deleted] 16 January 2012 07:22:46PM 2 points [-]

Building and running a church, paying for a bishops education and the time he works there, training children to sing, and all of the time people spend there is not a small investment. Multiply that by all the churches in the world, and add the cost of various missions and church plants to spread religion, or the charities which do their work sub-optimally because they take religion more seriously then saving lives and I imagine that the figure would become inappropriately ludicrous. Not that just eliminating religion would make us all much more efficient, humans are very gifted at wasting time and money.

Comment author: Swimmer963 16 January 2012 09:19:12PM *  2 points [-]

I've heard that argument before, and it does have a lot of weight. In this case, though, are we talking about religion or about costly ritual? Both are cultural phenomena, and they're frequently found together, but there are religions that aren't into ritual at all, like Quakers, who are best known for their simple, silent style of prayer and worship, and don't go around building fancy cathedrals). And there are costly "rituals" which are not related to religion at all: football, for example, or theatre.

Agreed that churches which run charities may run their sub-optimally from an atheist's point of view, since a lot of the time one of the unstated aims of their charity is to convert people. (This used to make me furious when I attended the Pentecostal church mentioned in one of the parent comments.) But we were talking about ritual, and I was specifically talking about deeply moving, meaningful rituals. It just so happens that the ones that have meaning to me are religious in nature. I know a lot of people find arts and theatre meaningful, and likely there are people who find watching sports meaningful, in a similar way. There's some kind of human instinct to gravitate towards activities that are communal, repetitive, and have a sense of tradition that imbues them with meaning. There's also a human instinct to think superstitiously, which I don't share much, and which makes it hard for me to really enjoy those meaningful moments in church.

Nitpick: yes, paying for a bishop's work and teaching children to sing is something that happens "under religion's umbrella." That doesn't make it bad! I learned to sing better through the church choir (for which I was paid a monthly stipend for the community service of singing during Sunday worship!) than I would have in the $400-per-month children's choir, which I probably wouldn't have been allowed into...most people thought I was tone deaf until I proved them wrong. Bishops who organize community events and charities are doing something good for the community, whether or not it's sub-optimal, and face it...are any human activities run optimally? Yes, it's possible to have a better community-runner than a church, but the amount of money that goes into churches right now does produce something of value!

Comment author: Swimmer963 16 January 2012 09:18:22PM 0 points [-]

I've heard that argument before, and it does have a lot of weight. In this case, though, are we talking about religion or about costly ritual? Both are cultural phenomena, and they're frequently found together, but there are religions that aren't into ritual at all (like <Quakers>(http://en.wikipedia.org/wiki/Quakers), who are best known for their simple, silent style of prayer and worship, and don't go around building fancy cathedrals). And there are costly "rituals" which are not related to religion at all: football, for example, or theatre.

Agreed that churches which run charities may run their sub-optimally from an atheist's point of view, since a lot of the time one of the unstated aims of their charity is to convert people. (This used to make me furious when I attended the Pentecostal church mentioned in one of the parent comments.) But we were talking about ritual, and I was specifically talking about deeply moving, meaningful rituals. It just so happens that the ones that have meaning to me are religious in nature. I know a lot of people find arts and theatre meaningful, and likely there are people who find watching sports meaningful, in a similar way. There's some kind of human instinct to gravitate towards activities that are communal, repetitive, and have a sense of tradition that imbues them with meaning. There's also a human instinct to think superstitiously, which I don't share much, and which makes it hard for me to really enjoy those meaningful moments in church.

Nitpick: yes, paying for a bishop's work and teaching children to sing is something that happens "under religion's umbrella." That doesn't make it bad! I learned to sing better through the church choir (for which I was paid a monthly stipend for the community service of singing during Sunday worship!) than I would have in the $400-per-month children's choir, which I probably wouldn't have been allowed into...most people thought I was tone deaf until I proved them wrong. Bishops who organize community events and charities are doing something good for the community, whether or not it's sub-optimal, and face it...are any human activities run optimally? Yes, it's possible to have a better community-runner than a church, but the amount of money that goes into churches right now does produce something of value!

Comment author: thomblake 11 January 2012 06:24:04PM 3 points [-]

Cheers!

-Stabilizer

Please do not sign your posts. That information is conveyed by the username listed at the top of the post.

Comment author: Peacewise 11 January 2012 03:45:58PM 1 point [-]

I was forced to conclude that debating was not about reaching the truth, but about proving the other person wrong. G'day -Stablizer,

Welcome to lesswrong, I'm quite new here too. I read your intro and think you would probably thoroughly devour Edward De Bono's "I am right, you are wrong". I agree with you regarding debating (and criticism) and so does De Bono, he writes about it quite elegantly.

Cheers, peacewise.

Comment author: [deleted] 11 January 2012 06:33:11PM 0 points [-]

I have a Physics question for you: is time continuous? I mean, is any given extent of time always further divisible into extents of time?

Comment author: kilobug 11 January 2012 06:46:53PM 2 points [-]

As far as I understand it : any time smaller than Planck's time (around 10^-43 second) is not meaningful, because no experiment will ever be able to measure it. So the question is kinda pointless, for all practical purpose, time could be counted as integer units of Planck's time.

Comment author: [deleted] 11 January 2012 09:41:28PM 0 points [-]

I've read that too, but I get confused when I try to use this fact to answer the question. On the one hand, it seems you are right that nothing can happen in a time shorter than the Planck time, but on the other hand, we seem to rely on the infinite divisibility of time just in making this claim. After all, it's perfectly intelligible to talk about a span of time that is one half or one quarter of Planck time. There's no contradiction in this. The trouble is that nothing can happen in this time, or as you put it, that it cannot be meaningful. But does this last point mean that there is no shorter time, given that a shorter time is perfectly intelligible?

Suppose for example that exactly 10 planck times from now, a radium atom begins decay. Exactly 10 and a half planck times from now, another radium atom decays. Is there anything problematic in saying this? I've not said that anything happened in less than a Planck time. 10 Planck times and 10.5 Planck times are both just some fraction of a second and both long enough spans of time to involve some physical change. If there's nothing wrong with saying this, then we can say that the first atom began its decay one half planck length before the second. This makes a half Planck length a meaningful span of time in describing the relation between two physical processes.

Comment author: Cthulhoo 11 January 2012 11:08:42PM 4 points [-]

Well, the correct answer up to this point is that we don't know. We would need a theory of quantum gravity to understand what's happening at this scale, and who knows how many ither step further we need to move to have a grasp of the "real" answer. Up to now, we only know that "something" is going to happen, and can make (motivated) conjectures. It may indeed be that time is discretized in the end, and talking about fractions of planck time is meaningless: maybe the universe computes the next state based on the present one in discrete steps. In your case, it would be meaningless to say that an atom will decay in 10.5 Planck times, the only thing you could see is that at step 10 the atom hasn't decayed and at step 11 it has (barring the correct remark of nsheperd that in practice the time span is too short for decoherence to be relevant). But, honestly, this is all just speculation.

Comment author: [deleted] 12 January 2012 03:22:22PM *  0 points [-]

Thanks for the response, that was helpful. I wonder if the question of the continuity of time bears on the idea of the universe computing its next state: if time is discreet, this will work, but if time is continuous, there is no 'next state' (since no two moments are adjacent in a continuous extension). Would this be important to the question of determinism?

Finally, notice that my example doesn't suggest that anything happens in 10.5 planck times, only that one thing begins 10 planck times from now, and another thing begins 10.5 planck times from now. Both processes might only occupy whole numbers of planck times, but the fraction of a planck time is still important to describing the relation between their starting moments.

Comment author: Cthulhoo 12 January 2012 10:41:47PM 1 point [-]

Warning: wild speculations incoming ;)

I wonder if the question of the continuity of time bears on the idea of the universe computing its next state: if time is discreet, this will work, but if time is continuous, there is no 'next state' (since no two moments are adjacent in a continuous extension). Would this be important to the question of determinism?

I don't think continuous time is a problem for determinism: we use continuous functions every day to compute predictions. And, if the B theory of time turns out to be the correct interpretation, everything was already computed from the beginning. ;)

Finally, notice that my example doesn't suggest that anything happens in 10.5 planck times, only that one thing begins 10 planck times from now, and another thing begins 10.5 planck times from now. Both processes might only occupy whole numbers of planck times, but the fraction of a planck time is still important to describing the relation between their starting moments.

What I was suggesting was this: imagine you have a Planck clock and observe the two systems. At each Planck second the two atoms can either decay or not. At second number 10 none has decayed, ad second 11 both have. Since you can't observe anything in between, there's no way to tell if one has decayed after 10 or 10.5 seconds. In a discreet spacetime the universe should compute the wavefunctions at time t, throw the dice, and spit put the wavefunctions at time t+1. A mean life of 10.5 planck seconds from time t translates to a probability to decay at every planck second: then it either happens, or it doesn't. It seems plausible to me that there's no possible Lorentz transformation equivalent in our hypothetical uber-theory that allows you to see a time span between events smaller than a planck second (i.e. our Lorentz transformations are discreet, too). But, honestly, I will be surprised if it turns out to be so simple ;)

Comment author: [deleted] 13 January 2012 08:52:11PM *  0 points [-]

In a discreet spacetime the universe should compute the wavefunctions at time t, throw the dice, and spit put the wavefunctions at time t+1.

Do you think you could explain this metaphor in some more detail? What does 'computation' here represent?

Comment author: thomblake 13 January 2012 08:59:22PM 1 point [-]

Just a side-note... I don't think this was supposed to be a 'metaphor'.

Comment author: [deleted] 13 January 2012 09:52:53PM 0 points [-]

Fair enough. How does the view of the universe as a computer relate to the question of the continuity of time?

Comment author: [deleted] 11 January 2012 10:03:55PM 2 points [-]

In your example you're using the term "now". That term already implies a point in time and therfore an infinitely divisible time. The problem is that while you certainly could conceive of a half planck time you could never locate that half in time. I.e. an event does not happen at a point in time. It happens anywhere in a given range of time with at least the planck length in extend. Now suppose that event A happens anywhere in a given timeslice and event B happens in another timeslice that starts half a planck time after the slice of event A. You can not say that event B happens half a planck time after event A since the timeslices overlap and thus you cannot even say that event B happens at all after event A. It might be the other way round. So while in your mind this half planck length seems to have some meaning in reality it does not. Your mind insists on visualizing time as continuous and therefore you can't easily get rid of the feeling that it were.

Comment author: [deleted] 11 January 2012 10:13:30PM *  0 points [-]

Why do you say that the time slices overlap? It seems on your set up, and mine, that they do not. The point seems to be just that nothing can happen in less than a Planck time, not that something cannot happen in 10.5 Planck times. The latter doesn't follow from the former so far as I can see. But I'm not on firm ground here, and I may well be mistaken. (ETA: But at any rate my example above doesn't involve anything happening in 10.5 Planck times. Everything I describe in that example can be said to occur in a whole number of planck times.)

And 'now' doesn't imply infinite divisiblity: we could have moments of time whether or not time is infinitely divisible, and we would need to refer to them to talk about the limit between two planck times anyway. And we cannot arrive at moments by infinite divisibility anyway, since moments are extensionless, and infinite division will always yield extensions.

Comment author: [deleted] 11 January 2012 10:21:20PM *  2 points [-]

Ah, english is not my native language. With "event B happens in another timeslice that starts half a planck time after the slice of event A" I meant timeslice B starts half a planck length after timeslice A started, so the second half of A overlaps with the fist of B.

B does not happen at 10.5 planck times after now. It happens somewhere between 10 and 11 planck times after "now" and you cannot tell when. Do not visualize time as a sequence of slices.

Edit: My point is, it's simply impossible to visualize time. If your brain insists on visualizing it, you will never understand. Because whenever you visualize a timeslice you visualize it with a clear cut start and a clear cut end. But that's not how this works.

Edit2: Maybe I'm just reading your response wrong. My point is that the precision in your example is the problem. There is no event that happens at a time with a precision smaller than one planck length. So 10.5 is just as wrong as 0.5.

Comment author: [deleted] 12 January 2012 03:20:05PM 0 points [-]

Ahh, I see, I think I misunderstood you. I'm not sure I understand why A and B overlap. The claim about Planck times is that nothing can happen in less time. Does it follow from that that all time must be measured in whole numbers of Planck times? A photon takes one Planck time to pass through one Planck length, but I can't see anything problematic with a cosmic ray passing through one Planck length in 10.5 Planck times. In other words does the fact that the Planck time is a minimum mean that it's an indivisible unit?

I don't think anything in my example relies on visualizing time, or on visualizing it as a series of slices. But I may be confused there. Do you have reason to think that one cannot visualize time? I suppose I agree that time is not a visible object, and so any visualization is analogical, but isn't this true of many things we do visualize to our profit? Like economic growth, say. What makes time different?

Comment author: [deleted] 13 January 2012 07:22:44AM 3 points [-]

The claim about Planck times is that nothing can happen in less time.

No. The claim is that nothing is located in time with a precision smaller than the planck time.

Comment author: [deleted] 13 January 2012 03:28:32PM 0 points [-]

I don't really doubt that you're right. Most everything I read on the subject agrees with or is consistant with what you're saying. But the idea is still very confusing to me, so I appreciate your explanations. Let me try to make my troubles more clear.

So far as I understand it, a Planck time is a minimum because that's the time it takes the fastest possible thing to pass through the minimum possible length. If something were going 99% the speed of light, or 75% or any percentage other than 100%, 50%, 25%, 12.5% etc. then it would travel through the Planck length in a non-whole number of Planck times. So something traveling at 75% the speed of light would travel through the Planck length at 1.5 Planck times. Maybe we can't measure this. That's fine. But say something were to travel at a constant velocity through two Planck lengths in three Planck times. Wouldn't it just follow that it went through each Planck length in 1.5 Planck times? It may be that we can't measure anything with precision greater than whole numbers of Planck times, but in this scenario it wouldn't follow from that that time is discontinuous.

Comment author: nshepperd 11 January 2012 10:49:16PM *  1 point [-]

For a start the classical hallucination of particles and decay doesn't really apply at times on the planck scale (since there's no time for the wave to decohere). There's just the gradual evolution of the quantum wavefunction. It may be that nothing interesting changes in the wavefunction in less than a planck time, either because it's actually "blocky" like a cellular automata or physics simulation, or for some other reason.

In the former case you could imagine that at each time step there's a certain probability (determined by the amplitude) of decay, such that the expected (average) time is 0.5 planck times after the expected time of some other event. Such a setup might well produce the classical illusion of something happening half a planck time after something else, although in a smeared-out manner that precludes "exactly".

Comment author: [deleted] 12 January 2012 03:28:55PM 0 points [-]

That's a good point about decay, but my example only referred to the beginning of the process of decay. I wasn't trying to claim that the decay could take place in less than one, one, or less than one trillion planck times. The important point for my example is just that the starting points for the two decay processes (however long they take) differ by .5 planck times. Nothing in the example involves anything happening in less than a Planck time, or anything happening in non-whole numbers of Planck times.

Comment author: kilobug 12 January 2012 03:46:02PM 0 points [-]

But the thing is : how can you measure that the decay differs by .5 Planck times ? That would require an experimental device which would be in a different state .5 Planck times earlier, and that's not possible, according to my understanding.

Comment author: [deleted] 12 January 2012 03:58:13PM 0 points [-]

Good point. I agree, it doesn't seem possible. But this is what confuses me: no measuring device could possibly measure some time less than one Planck time. Does it follow from this alone that a measuring device must measure in whole numbers of Planck times? In other words, does it follow logically that if the planck time is a minimum, it is also an indivisible unit?

This is my worry. A photon travels across a planck length in one planck time. Something moving half light-speed travels across the same distance in two planck times. If Planck times are not only a minimum but an indivisible unit, then wouldn't it be impossible for some cosmic ray (A) to move at any fraction of the speed of light between 1 and 1/2? A cosmic ray (B) moving at 3/4 c couldn't cover the Planck length in less time than A without moving at 1 c, since it has to cover the planck length in whole numbers of planck times. This seems like a problem.

Comment author: kilobug 12 January 2012 04:48:40PM 1 point [-]

It could be like that something moving at 3/4 c will have, on each Planck time, a 3/4 chance of moving of one Planck length, and a 1/4 chance of not moving at all. But that's how I understand it from a computer scientist point of view, it may not be how physicists really see it.

But I think the core reason is that since no signal can spread faster than c, no signal can cross more than one Planck length over a Planck time, so a difference of less than a Planck time can never be detected. Since it cannot be detected, since there is no experimental setting that would differ if something happened a fraction of Planck time earlier, the question has no meaning.

If time really is discreet or continuous doesn't have any meaning, if no possible experiments can tell the two apart.

Comment author: [deleted] 12 January 2012 06:45:25PM 4 points [-]

If time really is discreet or continuous doesn't have any meaning, if no possible experiments can tell the two apart.

Of course, given any experiment, spacetime being discrete on a sufficiently small scale couldn't be detected, but given any scale, a sufficiently precise experiment could tell if spacetime is discrete at that scale. And there's evidence that spacetime is likely not discrete at Planck scale (otherwise sufficiently-high-energy gamma rays would have a nontrivial dependency of speed on energy, which is not what we see in gamma-ray bursts). See http://www.nature.com/nature/journal/v462/n7271/edsumm/e091119-06.html

Comment author: [deleted] 12 January 2012 05:02:01PM 0 points [-]

The difference between discreet or continuous time is a concern of mine because it bears on what it means for something to be changing or moving. But I'm very much in the dark here, and I don't know what physicists would say if asked for a definition of change. Do you have any thoughts?

Comment author: Stabilizer 13 January 2012 02:59:28AM 0 points [-]

I'm sorry, I really don't know. In fact, I don't think I even know what the majority opinion is among physicists (if there is one).

At the face of it, it seems like if spacetime is discrete, then up until now, the unit of discreteness is small enough to allow us to do calculus (which assumes continuity) with impunity, even at the smallest of scales our experiments go to. So, as far as experimental evidence goes, there's no reason to believe in discreteness. But I guess your question is whether there are any theoretical arguments which suggest discreteness... to which I really don't have an answer. If I understand some interesting argument in the future, I'll get back to you.

Comment author: [deleted] 13 January 2012 08:49:55PM 0 points [-]

Thanks, I'll look forward to it.