<p>So I was blogging, and decided to write down some ideas about Life, the Universe, and ... Everything! A lot of people have come to me saying that the universe isn't deterministic, and such. Since there are so many MIT geniuses here, can someone explain to me why quantum mechanics says that the universe isn't deterministic?</p>
<p>The post in question is the 3rd post down(well... at least for now). </p>
<p>PS: Will MIT admin officers get really ****ed if I have a MIT Blog? I had one for about half a year, and nobody said anything, and it is really cool I think.</p>
<p>um, i don't see any post that resembles your question.
the short answer to your question is that qm basically simply casts everything into probabilities, and if you have exact total knowledge of a system you can then compute all the possible outcomes of that system and thus have a good probability distribution of how the system will behave, but that still doesn't help you figure out what will actually happen, only what might happen, and how often. and besides, it's hard to know exact initial conditions, so you're buggered before you even start.</p>
<p>Ok I read the entry on your blog (goddess is right, it was hard to find!). Isn't it the "God & Religion" entry?</p>
<p>Hmm so as far as the horizons of my knowledge extend, I believe at the root of this is the Uncertainty Principle.</p>
<p>Δx·Δp ≥ (ħ/2)</p>
<p>ie. The more accurately you know the momentum of a particle, the less accurately you'd be able to measure its position (and vice versa). This is more than just a practical limitation: it is a theoretical principle, applying to ideal measurements as well.</p>
<p>What this means is that we are limited by accuracy of measurement, since every measurement will consist of probable values rather than a consistent one. (The only accepted "accurate" value is c = 299792458 m/s exactly). So even if you had a totally deterministic model of the universe, you cannot predict the current state based on a previous state (or a set of measurements) with total accuracy. Thus, any prediction of the state of the universe at time t is a probabilistic measure. This in essence means non-predictability.</p>
<p>Many people confuse this with the universe being non deterministic. Predictabilty is a different concept. I strongly believe in this so-called film-roll theory - everything is pre-determined, but cannot be predicted until it happens (as you yourself wrote).</p>
<p>QM eliminates the idea of a defined state. nothing can be quantified with an infinitesimally small level of inaccuracy. QM thus talks not of particles, velocities, trajectories, etc in the same sense as Classical Mechanics does. There is no point particle of mass m which we use everyday to solve physics problems, simply because you dont know where the particle is and what it is doing. Therefore, instead of talking of definite quanities, we talk instead of the probability of the quantity/body having that particular value/attribute/so on. About it being indeterministic, i dont really agree. Just because you dont know the exact state of the system doesnt mean that it is indeterministic, but thats just a semantic argument for now for me. About not being able to predict what the particle will do next, thats because we still cant account for much of the force network acting on it. The nuclear forces are still not as clear as the gravitational force is, and the origins of such forces are still a subject of debate. Until we completely understand all there is to know about everything, we cant hope to predict what will happen then. QM acknowledges that, unlike newtonian mechanics where it is assumed that the interactions are reasonably well understood. The heisenberg uncertainity principle is basically an acknowledgement of the fact that you cant really know all the attributes of a system. To the layman, it may be explained that The act of observation changes that which is being observed. when you take a photograph, and the flashbulb flashes, the energy of the light is enough to change the system. The same goes for any kind of observation. </p>
<p>thats what you get in textbooks. or close to.</p>
<p>what i think :
the universe is deterministic. the human mind is incapable of handling the amount of data there is to even study an instant of a microscopic particles existence. All the computing power we have isnt enough to study all the particles of a small organism. We havent even come close to understanding the nature of interparticle interactions. And it isnt likely that itll be done in our lifetime. or our kids. The universe is too vast.</p>
<p>
[quote]
A finite mind cannot, by means of comparison, reach the ultimate truth of things. For by being by nature indivisible, the truth isnt subject to the concepts of more or less - nothing but the truth itself can be an exact measure of the truth.<something like="" that="">
<p>oh yes - as merc mentioned, the uncertainity principle refers to theoretical measurements as well - it isnt the error provided by flawed measureing devives/techniques.</p>
<p>shash, I believe you got something the wrong way around in your post. "The nuclear forces are still not as clear as the gravitational force is," should be the other way around. Whilst gravity is very well defined by General Relativity it cannot be incorporated into any Single theory that involves quantum mechanics at present. As a result, a two tiered physics world has formed, where General Relativity defines the universe because the gravitational force is predominant whilst Quantum Mechanics defines elementary particles since here the strong nuclear, weak and electromagnetic forces dominate. </p>
<p>In fact, Grand Unified Theory (GUT) has been extremely successful in defining the strong nuclear force as well as incorporating three of the four forces into a single theory. It has also been able to prove, quite categorically, that three of the four forces are the same, and therefore, originated from the same source. David J. Gross, H. David Politzer and Frank Wilczek won a Nobel Prize in physics last year for their work on asymptotic freedom and GUTs.</p>
<p>Yeah shashank, inuendo is right about gravity being the lesser-well understood force in terms of QM. Also:
[quote]
To the layman, it may be explained that The act of observation changes that which is being observed
[/quote]
Come on... you know that's not the reason. :p That will make it a practical limitation. It's a fundamental principle. QM nullifies all concept of "instantaneous" properties (infinitely small time intervals), so you need to measure the momentum (the velocity part) within a specific time frame (you need a period of time to measure it). But during that interval, the particle moves.. so position cannot be measured exactly. Same reasoning can be applied the other way round.</p>
<p>So - sagar - we are all with you ;) that the universe IS deterministic. Otherwise, the fundamental assumption of cause-and-effect (causality) is invalidated. It's just that we cannot really predict a state (as you argued). Keep in mind that U(t) is a state function with memory, i.e. U(t) depends on t as well as U(t-i), i->0.</p>
<p>1) There is this concept of "parallel universes" (arising out of trying to solve timetravel paradoxes). According to it, there exist an infinite number of parallel universes, each slightly different from each other (for every possible state of the universe). This might be fodder for those who believe the universe is indeterministic. Where are you guys? Come on.. :p (I have a few ideas to turn your argument the other way round ;) so beware).</p>
<p>2) If MIT made registering/updating a blog on their servers publicly accessible, I don't think they can complain if you have a blog on their servers.</p>
<p>it comes down to, of course, if the universe is deterministic, but we can't even compute/comprehend all the possibilities, does it really matter one way or another?</p>
<p>i'll refrain from muttering about "free will".</p>
<p>A wise cookie monster once said "Me love to look out the window at night. See all the pretty stars - twinkle, twinkle. You know what moon remind me of? It remind me of great, big , delicious cookie!"</p>
<p>So you all agree that the Universe is deterministic. Than where do people get all this crappy support for Intelligent Design. Most people I showed this too simply say, "You can't mix god and math."</p>
<p>Philosophy/spirituality is a superset of science. I would still go with the existence of God and, the fact that free will exists, and that miracles happen, that laws of physics can bend.</p>
<p>But in a purely scientific context, it's not possible, and as a scientist, I would deny this myself.</p>
<p>The difference lies in the fact that science is not the know-all be-all. It's a tool. And this is coming from someone who strongly believes in following a scientific approach.</p>
<p>I say : Go ahead and mix God and math, you'll find the ultimate solution. It's not impossible.</p>
<p>Heres the conflict. Part of my head says that as a scientist, I should believe that the Universe is deterministic, and there is no god, etc. The other part as a human says that there is god watchin out for me. Any of you get that same feeling?</p>