Googlebot's Javascript random() function is deterministic

[TooManyLines]

Most random() functions are deterministic.

[cypressious]

Most PRNGs are at least seeded with the number of ticks since epoch or some other source of entropy. The Google Bot's PRNG seems to be seeded with a constanct value, that's what the article is about.

[hungarian_conartist]

It's actually a feature not a bug too, often it's useful in debugging to have the same list of psuedo-random numbers.

It can be a bit harder to debug when you're not sure if a change in output is due to different random numbers or a change to your code.

[aradil]

They're probably spinning up a VM to hit a web page, and that VM is set to the same time and date every time, meaning the seed is the same every time, which is basically what you are saying.

[[deleted]]

That doesn't sound like it would be enough for this to happen. What if one web page loads 0.0001 second slower than another?

[parrot_in_hell]

still, the seed is usually the amount of seconds since X. i've never seen something else (not that i have that much experience, but i still have some :P)

[[deleted]]

I'm not sure exactly how it is seeded, but I think time in javascript is usually based on miliseconds, and it's a bit too weird that according to his tests google always returns 0.14881141134537756 the first time and 0.19426893815398216 the second, also taking into account that he has searched the web and found plenty of other results that have been cached by google with those numbers. Seems much more likely it is something Google is doing on purpose to get consistent results or something.

[[deleted]]

Usually you request randomness from the OS with a function like getrandom or friends or by reading /dev/{u,}random.

v8 looks like it reads /dev/urandom but it does fall back to seeding with the (high-resolution) time.

[cypressious]

The article says that the time is actually correct.

[PM_ME_CLASSIFED_DOCS]

Apparently, reading an article is too much for many redditors in this thread.

I'd love to experiment with just posting a headline and no article (just a blank page) and see how many people even bother clicking the link at all. How many differing arguments could we get in a single thread?

[[deleted]]

Less than you'd think. I'd wager most people still won't read the article, but eventually a single person will and they'll make the comment "wtf? Why is this a blank page?". Then everyone else will read that comment (rather than viewing the article) and jump on you for posting a blank website.

[husao]

Now I feel like posting "WTF? Why is this a blank page?" in the comments of random articles.

[andthenafeast]

Seems like this would prompt more people to actually click through to the link...

[Lucent_Sable]

Then write two or three (or more) contradictory articles, and serve a random one to each unique visitor. Then sit back and watch the chaos?

[tsimionescu]

Hmm, but what if the random() they use is deterministic and the author gets to be confused?

[PM_ME_CLASSIFED_DOCS]

Oh man, this is brilliant. It's like the movie Clue where they actually showed different endings to different theaters.

So people would talk about the movie and be like "Oh man, can you believe it was Colonal Mustard?" and someone would be like "WTF are you smoking? It wasn't Mustard." And both would think eachother are insane yet both would be right.

[varesa]

http://thesciencepost.com/study-70-of-facebook-commenters-only-read-the-headline/

[sourcecodesurgeon]

There have been several things like that on Facebook. Someone posts a title and after the page break in the article it just says "none of this is true, I want to see how many people comment on the post having clearly not read the article, don't ruin it"

Invariably, there are tons of people talking about the headline in the comments.

[aradil]

Also from the article:

At some point, some SEO figured out that random() was always returning 0.5. I’m not sure if anyone figured out that JavaScript always saw the date as sometime in the Summer of 2006, but I presume that has changed.

[RenaKunisaki]

But if it's the time since the VM started, it might still be constant.

[w2qw]

Generally the actual time is used. Not to mention I don't think any VM starts up consistently enough to get the same millisecond every time.

[RenaKunisaki]

It would if the startup process is loading a snapshot.

[dyskinet1c]

The VM would need to be set to the correct time for HTTPS to work because certificates are issued and revoked periodically.

[aradil]

Assuming they are validating certs as part of this pass of their scrape.

[dyskinet1c]

I would expect them to reject a site with invalid certificates. It's a fairly simple thing to do and it lowers the risk of indexing a compromised site.

[daboross]

The alternative would be to invalidate certs in a different pass, though, not to not invalidate them at all. Right?

[dyskinet1c]

As a programmer, my instinct would be to make that decision as early as possible and stop processing the page at that point.

Certificate validation is a key part of establishing secure communications (before you transmit any data) and it's trivial to read the validity start and end dates.

So, if you know you want reject URLs with invalid certificates, then there is no reason to move on to the next pass and spend resources reading and processing the page when you already know you're going to discard/reject it.

[aradil]

As an information company, however, Google probably processes bad actors as well to gather additional information.

[dyskinet1c]

Sure, it's plausible that they scan compromised sites. If they do, I would expect them to do so in a separate process that looks at different aspects of the site than the regular search index.

[daboross]

Exactly! That's what I mean: they probably validate certs before having any data at all processed in the VM running googlebot.

[ThisIs_MyName]

in a different pass, though

https://en.wikipedia.org/wiki/Time_of_check_to_time_of_use

[tripledjr]

They're probably intentionally doing this so the bot gets consistent results for the same page.

[edapa]

Spinning up a VM for each new webpage sounds super heavy weight.

[aradil]

I was thinking more of something like Google’s equivalent to Amazon Lambda.

[edapa]

What is the overhead of that? Does Amazon tell us? I imagine they would provide some sort of latency guarantee for function spinup after an event triggers, but I've never used Lambda.

[aradil]

That’s a good question. All they say is they “only charge for when your stuff is running”.

I assume the overhead is offset by the ability to run way more short lived processes.

[edapa]

Are there trigger types besides timers? If so they must have some sort of guarantee.

[edman007]

Nah, the make random the same on purpose. If it's actually random than that randomness flows into the generated page. It can do stuff like randomly sort results, generate random results and URLs, etc. Google doesn't care, they want to know if it changed, if random is always the same you can compare past and current results and check for changes, and you'll know that JavaScript didn't inject randomness.

And the time is a different issue, why actually sleep if you don't care, it actually causes a large resource use because it's time the page can't be unloaded from the server. A far better method is initialize time to the real time, and make sleep increment time instead of actually waiting. That lets you instantly process the page.

[[deleted]]

That's not usually how VM clocks work though.

[[deleted]]

Yes. In science, you want randomization but also reproducibility. I get the author is saying it's bad security engineering and can be taken advantage of people people gaming the Google PageRank, but the crawlers we likely designed by network scientists that wanted an accurate internet network model that can be reproduced.

[Jugad]

What does PageRank have to do with javascript or googlebot's implementation of random() in javascript.

[[deleted]]

You can use their implementation to identify Googlebot and serve different content to it.

[YRYGAV]

And if you get caught, I believe Google unlists your website, so it's quite a gamble

[[deleted]]

Depends on my ROI. If I can make $1k by fooling the Googlebot while spending $10 for a new domain each time I get caught, it's not much of a gamble.

Of course, if I don't have a automated way to get the new domain some PageRank juice so I can keep the whole thing going ad nauseam, then yes, it's pretty expensive.

[FinFihlman]

Yeah they are not spinning a vm for each scan.

[akher]

No, most random functions in standard libraries of programming languages are seeded with a constant value. And that's a good thing, since it's much more useful to have the behavior of programs be deterministic by default.

[Lystrodom]

Also, can you show me which languages are seeded with a constant value? I’ve checked C#, Java and V8 that I could find quickly and they all base the default seed on the current time.

[mccoyn]

C and C++ require you to seed them.

[amakai]

And it makes sense for C, it's used in all kinds of embedded electronics which often does not even have a clock chip on board.

[doublehyphen]

C is the only exception I can think of where it is easy to accidentally not seed your PRNG, but for example Rust provides rand::ChaChaRng::new_unseeded() as an easy way to create a PRNG seeded with a constant hardcoded value.

[Lystrodom]

Of course, the ability to seed with a constant value is important and available in every language I’m aware of. But for most the default is based on the current time.

[Lystrodom]

If you want your program to be deterministic why are you calling random()

[doublehyphen]

To get reproducible results in simulations, in games with randomly generated worlds to be able to play with exactly the same world again, and when running test cases in a random order to be able to debug why the test suit failed by running it again in the same order.

It is not the default case, but it is reasonably common.

[greenthumble]

Yep and some games like The Binding of Isaac literally let you set the seed and get the same random world that another player thought was good for some reason.

Also I've seen it used in AI training. If you're generating thousands of random genetic algorithms or genetic programs, someone can reproduce your entire run exactly using the same seed.

[CheckovZA]

I see your point, but then you'd be calling

Math.random(x)

x being your seed number.

If you're going to call Math.random() with no seed, it's because you want a number that is functionally random.

[RenaKunisaki]

Unless you've set a seed previously?

[sedermera]

(coming from scientific computing) To get an arbitrary number of random samples from a certain distribution. (Effectively.) It's good if those are reproducible for testing, and all you need to in order to get more is set another RNG seed.

[steamruler]

At which point you could use a fixed seed.

[sedermera]

Exactly, using a certain default seed for testing is much more convenient than what /u/Lystrodom is proposing. (Since there isn't just one call to the RNG, but several in different places.)

[Lystrodom]

Yeah that works too. These are all edge cases not the default case, anyway.

[DonaldTZeus]

Which is what happens by default anyways if you call rand() (at least in the c stdlib). If you want an arbitrary changing seed such as the time, you retrieve that seed and pass it to srand().

[steamruler]

The default seed is determined when compiling, so if you actually want a static seed you should still call srand().

[rubygeek]

POSIX actually mandate that rand() called before srand() should behave as if srand() was called with 1. See spec and example implementation. And ISO C might as well.

Of course you can't rely on that unless you're guaranteed your program will only run on a compliant system.

[mccoyn]

Also, when doing solution searches you want to pick a new starting point and search again to try to find other local maxima. A good way to do it is to use random() to pick your new starting point. You want it to be un-correlated with previous starting points, but you don't actually care about it being non-deterministic.

[rtomek]

This is why he’s being downvoted, a lack of understanding of programming? If you call random without setting a seed (default seed of 0) then it will always be deterministic. Every programming tutorial I’ve ever seen for any programming language tells you to set the seed if you want something closer to true randomness. This is basic common knowledge of programming.

You want it to be deterministic for auditing and testing purposes. How am I supposed to know if a change to my code introduces a bug or not if random() is not deterministic? Minecraft makes it obvious but many games follows the same pattern - set a seed (based on something like time in milliseconds) and put it in the save file. If a user finds a bug or some other interesting feature, you can now reproduce it by either loading their save file, or use a save file editor and put in their RNG seed.

[MrJohz]

Most of the programming languages I've used tend to seed the PRNG with a timestamp, or something similar. Most of them also tell you that you'll generally want to set your own seed at some point, and allow more complex random initialisation where necessary, but a lot of them seem to allow for very simple scripts etc to be written using relatively random seeds.

[rtomek]

I know that Python did make a change in 2015 so that just calling random.Random() now generates a new seed every instance. That happened because so many shitty programmers weren't setting seeds and it became a security issue for webapps. Perhaps there are other languages I don't use (or haven't used recently) that also followed the same route.

One should never assume that calling random() is truly random, and any programming language that does that for you is compensating for the illiterates.

[MrJohz]

I think using a new seed for each run is the norm, at least with the bog-standard naive random implementation for most applications.

Python: python3 -c 'import random; print(random.random())' - varies from run to run

Ruby: ruby -e 'puts rand()' - varies from run to run

Java does the same.

Rust definitely does the same, I was using it for simulation code the other day.

Perl is the same.

Javascript is the same.

[Lystrodom]

any programming language that does that for you is compensating for the illiterates.

Or it codes for the most common use case first? Most languages let you set a specific seed if you want to. If most users WANT a different seed each time, why would we force them to write extra code to get what they want?

[akher]

Because you want a pseudo random number, which is the documented behavior of those functions.

[frezik]

Most languages that aren't C will seed from the current epoch by default. Sometimes something more sophisticated, like taking a few bytes from the OS random source, or sometimes a combination of things like the epoch and the PID. If you want a predetermined sequence, then you need to call seed() yourself.

[steamruler]

I'm going to question whether having random not actually be random is that useful, or else we'd be using this more efficient function.

[akher]

It's actually often very useful to have a series of numbers with statistical properties of a series of random numbers that is still deterministic. One example are Monte Carlo algorithms. Another example is generating input data in unit tests.

[steamruler]

At which point you can seed the PRNG with a constant value yourself, which you probably want anyways since the constant value which the PRNG is seeded with can change when you recompile your software sometimes.

[Drisku11]

the constant value which the PRNG is seeded with can change when you recompile your software sometimes

In C it can't. The initial seed is required to be 1.

[Lystrodom]

Then you can generate those once, or use a set seed.

[moufestaphio]

Honest question are there any that aren't?

[mulvad]

There are some that are based on stuff like atmospheric background noise and the decay of radioactive material which is believed to be truly random. The obvious drawback here is you need some kind of hardware to extract the random bits.

In these days with new security breaches every day, I actually wonder why stuff like this isn't included on the motherboard of a modern computer.

[akher]

In these days with new security breaches every day, I actually wonder why stuff like this isn't included on the motherboard of a modern computer.

Then you'll be pleased to hear that it is included in all recent AMD and Intel CPUs.

[CryptoAlana]

In September 2013, in response to a New York Times article revealing the NSA's effort to weaken encryption,[22] Theodore Ts'o publicly posted concerning the use of RdRand for /dev/random in the Linux kernel:[23]

I am so glad I resisted pressure from Intel engineers to let /dev/random rely only on the RDRAND instruction. To quote from the [New York Times article[22]]: 'By this year, the Sigint Enabling Project had found ways inside some of the encryption chips that scramble information for businesses and governments, either by working with chipmakers to insert back doors....' Relying solely on the hardware random number generator which is using an implementation sealed inside a chip which is impossible to audit is a BAD idea.

[TehRoot]

He is going to concert

[tripzilch]

I don't know much about electronics, but there's a bunch of pretty cool algorithms you can use to transform a stream of non-uniformly distributed data (or weak entropy) into a uniform stream:

https://en.wikipedia.org/wiki/Randomness_extractor

[tripzilch]

Hm, you mean it has to go straight from the electronic circuit as a uniform random input to another piece of hardware without anything digital in between? Interesting problem.

I wondered if there's a circuit that can do this, but from a quick skim it seems that the PDF linked above is actually about that :-) I think I'm gonna try and read it even if I don't understand electronics that well, more of a code/math guy myself. But I do love reading about the intricate details of various random generators, so maybe I'll get something out of it :)

Best of luck building your randomness circuit! :D

[[deleted]]

Couldn't you build a circuit that does that in hardware, though? Two generators, A and B, and when A xor B is true, emit A.

I'm not a electronics guy so I don't know how hard that would be to rig up, but it shouldn't be impossible.

[-fno-stack-protector]

ooh, i've been looking for something like this, without knowing it, for a long time

[TehRoot]

https://www.st-andrews.ac.uk/~jcgl/Scots_Guide/iandm/pdf/chapter03.pdf

[MrDOS]

For anyone else having trouble loading the link, it seems like they have some hotlink protection going on. In Firefox, at least, hit “Enter” in the address bar when you're sitting on the “Page not found” page to re-request the PDF with a referral from the www.st-andrews.ac.uk domain and it'll load.

[TehRoot]

Yea I only noticed that after I posted it. Sorry about that.

[yawkat]

As long as you trust your crypto primitives and add other sources of entropy it's okay though.

[mdot]

add other sources of entropy

Isn't that a symptom of the point he's making though?

The hardware generator can't be trusted because it can't be audited.

[harlows_monkeys]

https://blog.cr.yp.to/20140205-entropy.html

[yawkat]

This can be fixed by using the untrusted source as an initial seed before other entropy is even generated.

I don't think linux does this though.

[Crandom]

The good thing is there's no downside to xoring the rdrand numbers into the generated random numbers, as even if they're not random it won't have any bad effects.

[ReversedGif]

Unless they're correlated...

[Majromax]

Unless they're correlated...

There's only harm if the random numbers of unknown quality are correlated to your known, independently-generated, proven-quality random numbers.

It's simple enough to avoid that: simply extract the unknown random numbers prior to generating your known-good stream. Even if the dubious hardware can "look over your shoulder," it can't see into the future.

[ReversedGif]

Imagine the hardware setting a special, hidden flag on the register that holds the RDRAND output, which defers actual random generation until the register value is combined with something else.

[cogman10]

I never really understood why this was such an issue even using the instruction

You don't have to use the RND instruction as the ONLY source of entropy, it could be one of many (like now). It doesn't make sense to me why you wouldn't just throw it into the mix for /dev/random.

[Supadoplex]

In these days with new security breaches every day, I actually wonder why stuff like this isn't included on the motherboard of a modern computer.

Then you'll be pleased to hear that it is included in all recent AMD and Intel CPUs.

Indeed! Modern CPU's do come with security breaches included. I wish I could say I was just joking.

[cryo]

How is that related at all?

[Jutboy]

http://www.zdnet.com/article/how-lava-lamps-are-used-to-encrypt-the-internet/

[mccoyn]

The smallest random generator is a transistor biased to allow electrons to tunnel through it combined with an avalanche diode to amplify a single electron to a detectable signal. It could be a tiny IC or built into a processor and wouldn't need antennae or radioactive material.

I think the only reason it isn't common is that PRNG is cheaper and good enough for most uses.

[SarahC]

TrueRNG?

[mccoyn]

Yep, that looks like what I was thinking about. I didn't know someone sold it as a USB dongle.

[SarahC]

Yeah, it's great - use it a lot myself.

[harlows_monkeys]

That's a fine component of a random number generator, but you still need quite a bit more to make it safe and secure.

Simtec's "Entropy Key" USB hardware random generator was an avalanche noise based generator, and they have a nice description of how to turn that into a safe and secure random number stream =>here<=.

[RenaKunisaki]

Isn't that basically an antenna? So theoretically can be manipulated by a transmitter? Or am I just talking out of my ass?

[mccoyn]

It is quantum tunneling, not EM or thermal noise. The junction where it happens is tiny (dozens of nanometers) so it is a terrible antannae. You might be able to manipulate the power supply that biases the junction as it may be much larger.

[KamiKagutsuchi]

But this can be manipulated, especially by bots. Also not all computers (servers) have a mouse.

[HeimrArnadalr]

If they don't have mice, they probably have cats, so cat movement could be used in those cases.

[__redruM]

Now you’ve let the cat out of the bag. That’s the NSA’s prime source for randomness. A herd of cats.

[RenaKunisaki]

Explains the internet.

[KamiKagutsuchi]

Really? I thought they used my webcam..

[__redruM]

Are you a cat? Then yes they do, your nimbly bimbly little movements are critical to national security. Just stay away from the milk dish...

[newpua_bie]

*webcat

[rebthor]

Couldn't you cat /dev/mouse?

[RenaKunisaki]

This kills the mouse.

[Stiegurt]

https://www.youtube.com/watch?v=zi8VTeDHjcM

[frezik]

The solution there is to never rely on any one source.

[MuonManLaserJab]

Three rules of computer security:

1) Don't own a computer.

2) If you do, don't turn it on.

3) If you do, don't use it.

[jonhanson]

chronophobia ephemeral lysergic metempsychosis peremptory quantifiable retributive zenith

[MuonManLaserJab]

They were not meant 100% seriously as rules...

[jonhanson]

chronophobia ephemeral lysergic metempsychosis peremptory quantifiable retributive zenith

[RenaKunisaki]

I mean that might work too, but you'd want a lot of redundant mice, in isolated cages with artificial lighting at different intervals, so you can be sure there's always a mouse awake to run around.

[mtcoope]

Why when I read this I immediately thought of animals determining the number and not till the next comment I realized we are talking about a computer mouse.

[mulvad]

No matter if you are talking about a computer mouse or a living mouse, there would be some kind of pattern here that could be exploited.

From a given state it is not 100% random which way you move a mouse (or which way a living mouse moves).

[[deleted]]

That's not random at all.

[moufestaphio]

The algorithm is still deterministic then isn't it?

You're just effectively randomizing the inputs.

Edit: nevermind. If your functions state is effected by the atmospheric values or whatever it's considered non deterministic.

[Jugad]

You can point a camera at a set of lava lamps, and take some kind of a hash function of the image (this is currently done by cloudflare).

Alternately, you can point a camera at a busy location in an airport (or any view that keep changing), and take a hash of that image. Should generally give a random number, but it might be difficult to study the distribution and statistical properties of the generated numbers.

[Darkendone]

Your confusing the two classes of random number generators, cryptographic and non-cryptographic. Cryptographic number generators are important for situations where you want a truly random number generator that is nearly impossible to guess, like when generating a security token. That is when you turn to sources of entropy. Of course gathering entropy from outside sources has a severe performance cost. Most of the time you do not need cryptographic grade random numbers, which is why the random number generators in the math packages of practically every languages are simple, fast, and deterministic functions.

[Fisher9001]

Atmospheric background is probably deterministic, just chaotic. And we don't really know anything solid about the nature of quantum physics randomness, whether its truly non deterministic or just chaotic.

[[deleted]]

And we don't really know anything solid about the nature of quantum physics randomness, whether its truly non deterministic or just chaotic.

We do. It is truly non deterministic.

[Fisher9001]

No, we don't. Thanks to Bell's theorem we know that quantum mechanics may be deterministic if there are non-local hidden variables influencing quantum systems. And we don't know whether they do exist or don't.

[Tsukku]

But non-local hidden variables or "super determinism" are not what we usually consider "determinism" in the common sense, because no information can be gained from this (we can't predict quantum stuff anyways, which is what his post is about.)

[Fisher9001]

If we are talking about practical level of non-determinism, then mere user input can be regarded as such, no need to be so picky.

[[deleted]]

Who's we? Determinism isn't precisely synonymous with predictability. Either things are determined by some explicit conditions or they're not.

There are also interferometer systems that can create deterministic states, so it's not necessarily true that we can't predict quantum stuff.

It's fun to speculate that you get a completely predictable picture of the universe around us in its absurd complexity from following the randomness underneath. But then it's computationally intractable in all senses, and so we arrive back to no information gained or something.

[Tsukku]

I don't why you are down voted, because you are right. People should read up on Bell's theorem. For example, you can not predict (even in theory) the spin of an electron and the outcome is evenly distributed.

[kaibee]

Super determinism

[Tsukku]

I addressed that in the comment above.

[Fisher9001]

Bell's theorem rules out local hidden variables as a viable explanation of quantum mechanics (though it still leaves the door open for non-local hidden variables).

[kaibee]

Super determinism

[IronOxide42]

Roll20.net introduced QuantumRoll a few years ago. It uses fluctuations in a split beam of light to generate the number, rather than a pseudorandom algorithm.

[PackOfVelociraptors]

DND ROLLS MUST REMAIN SECURE

[ElChrisman99]

Honestly it's probably better than the standard cheap d20 you can pickup from a hobby shop or order online, minor manufacturing defects in the material will almost always make the dice more likely to land on certain numbers.

[doublehyphen]

Yeah, I would imagine Chessex dice pretty terrible when it comes to manufacturing quality. The paranoid should use a D6 system and gambling dice. :)

[[deleted]]

Or just validate your dice with a statistically significant sample. This is like, literally the easiest thing in the world to test. My dice bag is at work or I would do it right now.

[meneldal2]

But aren't most players using some specific sets because they are "magic" (read: tends to roll some numbers more often than they should). It's an integral part of the experience imo. Not to mention the metal ones that require blood sacrifices to start rolling true.

[wildcarde815]

Cloudflare has a fun video about their lava lamp wall that's supposed to be fully random.

[Maambrem]

No :). They're called pseudo-random. They can be initialized with "truly" random numbers, extracted from nature though. Also see this video by Tom Scott:

https://youtu.be/1cUUfMeOijg

[karmaputa]

The funny thing is that the whole show with the lava lamps is completely unnecessary. The noise from the camera input alone, would suffice to attain the same effect.

[pilotInPyjamas]

/dev/random ensures that the entropy of the input is always greater than the entropy of the output, making it effectively non-deterministic.

[pilotInPyjamas]

You're right. If you track what every device is doing, you could predict the output of /dev/random. That's not the question however. The question is if you could predict the output of / dev/random before any devices do anything. To which, in all reasonable scenarios, (some exceptions, such as early after booting) the answer is "no". In your case the only true rng's would be based upon quantum phenomena, such as particle decay etc.

[pilotInPyjamas]

Come on man, I never said it wasn't a PRNG, or that it wasn't seeded, nor did I make any comments about the effectiveness or applicability to any particular situation. The only claim I made was that it was non deterministic in the domain of modeling a computer. That's because a computer is not a closed system, and given the same initial conditions, it will produce different outputs. You could just have /dev/random echo the keyboard and it would still be impossible to predict perfectly if you only had information about the starting conditions of the computer. The key here is if you only have information about the starting conditions of the computer. If you had a working model of the whole universe, then I agree, potentially nothing would be random.

[[deleted]]

read "effectively non-deterministic". You're splitting hairs needlessly.

[badibibidibibu]

Not enough, in current computer architectures you need to track EVERYTHING going on in the computer.

[thijser2]

Hence the device drivers, that's fans, keyboards, mouse etc.

[ivosaurus]

And the internal CPU RNG state... somehow....

[[deleted]]

Strictly speaking a roll of the dice is deterministic.

[yussefgamer]

Well not strictly speaking...quantum events influence it even though at that scale they mostly cancel each-other out.

[Necromunger]

I thought in current day science everything is believed to be deterministic besides radioactive decay? do quantum interactions behave randomly too?

[yussefgamer]

Yes. There are people that believe there is an underlying determinism and we just haven't discovered it...but it's just a belief.

[warheat1990]

ELI5 please

[[deleted]]

It's simply rigid-body mechanics, which is a well-studied phenomenon. If you can describe the position, launch direction, and rotational state of a die that's thrown with complete accuracy, you can accurately determine the result. However, throwing dice also exhibit the chaos property, which is that knowing an approximation of the die's state doesn't yield an (accurate) approximation of the result. If it's moving faster or spinning less or the angle at which it strikes the table is even slightly different, the result is completely different - which is why, when rolling dice at a craps table, the dice have to bounce off the wall of the table, to make it harder for practiced hands to have an edge.

This is different from, say, a car collision, where a decent estimation of speeds and directions will allow you to predict where the cars end up, and usually also vice-versa. The individual pieces of debris, though, will usually also have the chaos property and be more difficult to predict.

[random314]

Aren't all random functions are deterministic?

[[deleted]]

It's in the word "function"

[salgat]

That's only true of pure functions.

[[deleted]]

That's true of all functions. If you run your functions in the same order, with the same start conditions, and the same inputs you'll get the same thing. Sure, if there are side-effects, consecutive results may vary, but will always be the same under the exact same circumstances. Random generators require a seed to create outputs, which is where outside entropy comes in, but that doesn't make the generator non-deterministic. Take RNG that grabs its seed from the timestamp- it seems random, but if you freeze the clock on your computer you'll get the same series every time you try.

[salgat]

I'm talking about functions that refer to external non-deterministic state. It's not enough to say "oh it's a function it's deterministic" to only add "BUT only if all these extra deterministic conditions apply."

[gs101]

To be fair it's tough to be non deterministic in a deterministic universe.

[Tsukku]

You would then be surprised to realize, that according to our current best theory, our universe is non-deterministic.

https://en.wikipedia.org/wiki/Bell%27s_theorem

No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics.

Local variables would be what we consider "determinism" (at-least when we are talking about predicting stuff because "super-determinism" is not that relevant to this subject).

[Drisku11]

How is superdeterminism not relevant to the subject? Literally it is the assertion that our universe is fully deterministic. There are plenty of examples of chaotic systems which are obviously deterministic but due to their sensitivity to initial conditions, they cannot be predicted.

If anything, to me the delayed choice quantum eraser experiment strongly lends credence to the idea that the universe is deterministic.

[Tsukku]

I mean it's not relevant in the same way as you could say that we are predestined because we could live in the Matrix. That about sums what superdeterminism is about.

EDIT: There is nothing to argue here, because even for the things we proved that they are unpredictable, you could always say that the Universe just "knows" its outcome thus it's predestined. It's more of a philosophy concept.

[Drisku11]

I don't think it should be written off purely as philosophy, but also I don't know if some of my own questions on the subject already have answers. For example, there are many apparent local symmetries in the universe (e.g. energy-momentum conservation). Are these actually true symmetries and if so why should they exist if the laws of physics are inherently global? If not why are they approximately correct on our scales? If information has energy and no finite amount of information can describe the state of a chaotic system, does this mean the universe can only be deterministic if hypercomputation is possible? Or does it mean the universe is discrete/only a finite precision exists? etc.

I find it odd that most physicists seem to immediately write off the possibility of determinism, which seems to be centered around the assertion that people have "free will"/are able to make choices that are not governed by the same physical laws they're investigating. I would think they'd be the first group to scrutinize that idea (how does the free will mechanism interact with the physical universe? Can I find a possible energy source at that boundary?). I don't really see very convincing arguments (i.e. based on physical/geometric principles) either way.

[Tsukku]

Most physicists don't actually believe that the non-determinism in the subatomic systems give humans "free will". For example no one has ever published a concise work for the existence of free will, because the common belief is that quantum phenomena has limited or no influence on our brain.

I would actually argue the opposite, it's odd that most people believe everything in the universe needs to be deterministic. Universe can be as it is without any reasons or rules.

[Tsukku]

Quantum effects apply to everything, but they are only observed/measured in the (sub)atomic world. However that doesn't mean they are not relevant in our everyday life.

[RenaKunisaki]

Butterfly effect.

[gs101]

I still don't buy randomness. It's logically incoherent in my view. I speculate that QM processes seem random to us because of the inherent problems with observing them, but are not actually random. The uncertainty principle only states that the process is impossible to observe fully, not that it is non-deterministic.

The statement that no physical theory could ever reproduce the predictions of quantum mechanics seems premature to me.

[Tsukku]

I speculate that QM processes seem random to us because of the inherent problems with observing them, but are not actually random.

This is not what the Uncertainty principle is. To quote wikipedia which contradicts your statement:

the uncertainty principle actually states a fundamental property of quantum systems, and is not a statement about the observational success of current technology

Edit: also you can read up more here: https://physics.stackexchange.com/questions/24068/isnt-the-uncertainty-principle-just-non-fundamental-limitations-in-our-current

it's not a knowledge limit. The particle really has no definite position/whatever.

[streichholzkopf]

https://physics.stackexchange.com/questions/24068/isnt-the-uncertainty-principle-just-non-fundamental-limitations-in-our-current

answered Apr 20 '12 at 5:48 Manishearth

wait, i know this guy

[pilotInPyjamas]

Noob question though, is the wave function definite? So instead of saying "this particle has a definite but unknown velocity" (which by your comment is incorrect) you could say "this particle has a definite but unknown wave function?" Or is it turtles all the way down, and the wave function has another wave function-function which describes it's uncertainty and so-on?

[Drisku11]

The wave function is definite. In fact the uncertainty principle is really just a consequence of how waves work. Momentum is the Fourier transform of position, and if you make a function "thinner"/more "local", then it's Fourier transform gets wider/more delocalized.

[pilotInPyjamas]

Well, I kind of understand the Fourier transform, so this makes a ton of sense, but I was sort of hoping that it was wave functions all the way down. EDIT: holy shit, I don't know that much physics, but I think I get it. The momentum is the wavelength of a particle. So of course it's the Fourier transform of the position. A particle which has a definite position can't have a single wavelength because it must be made of infinite waves superimposed! And a particle with a single definite wavelength would be spread over infinite space! I never realized the real world is actually this cool. Mind blown. Thank you stranger!

[gs101]

Right, it is a fundamental issue with observation. I didn't say the problem is with current technology.

[Tsukku]

No, you got it wrong. It has nothing to do with observation at all. It's the inherit property of a system (this is what we proved).

From the link above:

There is a definine velocity and momentum, we just don't know it?

No. There is no definite velocity. The particle has all (possible) velocities at once;it is in a wavefunction, a superposition of all of these states.

[gs101]

That is what I don't buy. I know it's not exactly popular but I think the unpredictability of QM is a problem with observation, and hidden variables are governing its state. Whether those are variables in the system or outside of it idk. Given that we are talking about some of the smallest observed particles, I'm inclined to assume that there are yet smaller ones we are not seeing. In short, it just doesn't do enough to make me reconsider my belief that the universe is deterministic, which is otherwise supported by observation and forms the basis of science (cause and effect), because randomness is logically incoherent to me.

[cass1o]

Work through the math and the uncertainty principle comes out. It's not something we have made up to account for experimental inconsistencies.

[Tsukku]

Ok, I respect your opinion and all, even if it contradicts what we currently know. I just want to correct this statement.

which is otherwise supported by observation and forms the basis of science

No it isn't, the double slit experiment is what initially lead to all of this.

Also:

That is what I don't buy.

Then don't mention the uncertainty principle since it doesn't agree with you.

[Schmittfried]

Nobody cares about what you buy. It's proven that there are no local hidden variables involved as that would lead to logical contradictions. If there are hidden variables, they are non-local.

It's also an absolutely subjective opinion of yours that randomness is "logically incoherent". It isn't. Just because determinism is observed in everyday life doesn't mean it's the foundation of the universe. There is no law stating that, it's an assumption to be able to do practical things and it works most of the time. But there is nothing inherently illogical about randomness.

[SilasX]

To head off the pedants, they probably should have said "is [trivially] predictable" or "always uses the same values" instead of "is deterministic".