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sina89
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maybe this is too basic question but it is not so clear for me. when we refer to a random experiment, can a phenomenon be absolutely random by itself or its all about our uncertainty about the outcome that we call it random?
FactChecker said:It is called a "superposition of states" when something exists but its state is not fixed. (I hope I am not butchering this)
chogg said:Contrast this with the case of quantum mechanical density matrices, where there really isn't a definite state.
FactChecker said:I believe that this is what I was trying to remember -- an entangled pair where there isn't a definite state. Isn't this is an example of something that is intrinsically random?
chogg said:OP: are you asking whether the universe is "ultimately" determinsitic vs. stochastic?
If so, there is some interesting discussion on a (closed) thread here:
https://www.physicsforums.com/showthread.php?t=384130
The parts I find most interesting are on Page 2.
I still hold the basic position I explained in that thread; we simply do not know whether the universe is ultimately stochastic or deterministic.
sina89 said:so can i conclude your statements as " there is consensus today among physicists about intrinsically random states, and they all(or mostly) believe that einstein's point of view is PROVEN wrong"? if quantum actually did prove this,
FactChecker said:@sina89, I hope this is not hijacking your OP, but I think it goes to the hearth of your question. There were situations in quantum theory where there was a debate as to whether a system was in an internal "hidden state" that we just could not determine (Einstein believed this), or if its state was really still uncertain. I have been calling the latter case "intrinsically random", but @chogg has explained that this is a system with a density matrix. The thread he points to is very interesting. But I thought that the issue was settled. Experiments have been done where the probabilities of outcomes were different in the two cases (in a hidden state versus still random with a density matrix) . The results of the experiments showed that the system was not in a "hidden state". It was still in no fixed simple state, but rather has a density matrix. I think that this indicates that there are truly random processes.
Chronos said:Statistically, it is impossible to prove the result of any process is truly random. Even a coin that comes up heads 1000 consecutive times still has a much higher statistical possibility of being a 'fair' coin than you might suspect. To achieve a 3 sigma confidence interval on a pass - fail basis, you need nearly 1100 consecutive 'pass' outcomes, and there is still about a 1 in 370 chance it was just blind luck.
chogg said:Quite so: local hidden variable theories have been ruled out.
The (main) reason I say randomness is an open question is this: the time-dependent Schrodinger equation is deterministic. The quantum state of your system evolves smoothly: if you know it at one time, you know it at all times.
Chronos said:3 sigma corresponds to a 99.73% probability a process output will fall within a certain range of values. For an analog output [measured numerically], it follows a gaussian distribution. For a discrete output [pass fail], it follows a binomial distribution. Sigma is the term used to express the probability an output will fall within certain limiting values. 3 sigma is generally considered a reasonable probability a process output is, or is not random. In some applications, 3 sigma is considered pretty sloppy and higher confidence intervals are demanded [e.g. particle physics]. You can characterize the probability any particular outcome, or series of outcomes is, or is not random, but, never with certainty.
I've just read this short article about it:sina89 said:maybe this is too basic question but it is not so clear for me. when we refer to a random experiment, can a phenomenon be absolutely random by itself or its all about our uncertainty about the outcome that we call it random?
Random just means unpredictable. It is subjective. An event may be random to one observer and not random to another.sina89 said:maybe this is too basic question but it is not so clear for me. when we refer to a random experiment, can a phenomenon be absolutely random by itself or its all about our uncertainty about the outcome that we call it random?
Erwin's pet tells another story.Hornbein said:I think not: that is, we can never be sure that certain types of events will never be predictable. But...who knows? It's just my opinion.
mpresic said:This is not a easy question at all. I read a story somewhere (I do not have the reference) where astronomers needed to select a random star. First, one astronomer proposed to use the computer to generate a random point (ascension and declination). Then look at a sky map to find the nearest star to that point. One would think that would generate a random star. Another astronomer thought to label all the stars from 1 to 1 trillion (or so). Get the computer to generate a random number and the star corresponding to this point would be the random star. A third astronomer chose to do some other procedure (I do not remember).
The point is these are three different algorithms which will lead to far different results. Another illustration from probability textbooks (e.g. Papoulis, Probability, Random Variables, and Stochastic Processes) is labeled the Buffon's needle problem. Three different ways to implement "random" lead to three different probabilities (1/4, or 1/3, or 1/2) the "random" chord generated on a circle has a greater length than the side of a equilateral triangle inscribed within that circle. All three answers can be interpreted as correct.
I think there is one more think to say about "random" as it is used to describe physics - and I'll try to describe it as non-technically as possible. I will use a binary measurement as an example - a measurement that results in one of two results. A QM experiment can be set up where "locally" the result of the measurement is entirely unpredictable - as if a bit of information had been added to the universe completely unknown and unknowable to that measuring site. However, if the state being measure is entangled, then another QM experimenter a distance away may be discovering that same information.sina89 said:Thank all of you for reply. I am new here and i didn't know where to post my question. i wanted to what do people exactly mean when they use the word RANDOM in physics.
Randomness is the lack of pattern or predictability in a sequence of events. It is closely related to uncertainty because it means that the outcome of an event cannot be predicted with complete certainty.
Randomness can be measured and quantified using statistical methods such as probability and entropy. These measures can help determine the degree of uncertainty present in a given situation.
Examples of randomness and uncertainty can be found in various aspects of life, such as weather patterns, stock market fluctuations, and the outcome of a coin toss. These events cannot be predicted with absolute certainty due to their inherent randomness.
Randomness plays a crucial role in scientific research, particularly in fields such as statistics and genetics. It allows for the exploration of new patterns and relationships, and helps scientists make predictions and draw conclusions from data.
While randomness itself cannot be controlled or manipulated, its effects can be mitigated through the use of statistical techniques and experimental design. However, true randomness cannot be fully eliminated as it is a fundamental aspect of the natural world.