I have a question for physicists...

Falsey wrote:Im almost 100% certain Ive seen a video of a pool playing robot before, but the big hitch is that the robot itself set the position of the balls. I believe it was a demonstration on the precision of industrial robots, so it obviously had to display the precision and reliability to be an effective sales pitch - and industrial robots arent known for their 'on the fly' decision making ability.

Also it was only a cue to object ball interaction. I maintain that even if the robot was programmed to set the balls in exactly the same way and strike in exactly the same way each time, the break pattern would be so diverse that anything beyond the first shot would be impossible to anticipate.

That's interesting, it's cool it's been thought about. You're right, you'd need some pretty hefty heuristics and some custom laser-imaging hardware (for precisely measuring ball locations) to play a 'dynamic' game rather than a tech demo. I think it's possible, but if there were rules about the time it had to 'think' about each shot then that would make things more difficult. I think you're right too that the break at the start just wouldn't be predictable -- the robot, I suppose similarly to a human, would want to just disperse the balls and then decide what to do next.

It would be interesting to watch -- I suspect the robot would win out over human players eventually, certainly given enough funding for team robot to make a proper go of it (like IBM's Watson supercomputer eventually getting unbeatably good at chess!).

I absolutely think a team with sufficient funding and resource could develop a robot to win at pool every time in a fairly short space of time. The precision and dexterity of your standard industrial robot makes the mechanics of playing the game elementary.

Would they be able to program a robot to break the balls with an intending final lie? Not a chance. The closest they would get is the same thing a human player aims for - a good split with at least one down for the opportunity to win in a single visit.

I'd love to see the algorithm for 'putting some English on it'.

Karl wrote:"Does true randomness exist?" Yes: small enough things behave truly probabilistically. Quantum mechanics is really, physically nondeterministic. You can construct a system, such as a hydrogen atom in its ground state, and watch the movement of the bound electron. The location of the electron in that system does not follow a pattern: it can appear anywhere within its 'probability cloud' at any time. There are experiments we can do, such as the 'double slit experiment' which prove that this isn't just a case of not knowing enough about the system's initial conditions or environment: the particles behave as though they are 'smeared out' whenever they aren't being actively looked at.

"Can you predict the location of billiard balls on a bouncing table given enough information?" Eventually quantum effects would have a randomising influence, so no, not to arbitrary precision or on arbitrarily long timescales. To see how this works, imagine you have a Universe with some (idealised and electrically neutral) billiard balls bouncing on a frictionless table in empty space, with one far-away electron. The electron's location is random, but it does still interact gravitationally and influence the bounces in a random way. One ball-park figure the lecturer in my statistical mechanics course a few years ago suggested was that each ball would have to have roughly 50-100 bounces before your prediction (sans electron) and the reality noticeably no longer matched up.

This, then, I would think, is perhaps one of the strongest arguments against the concept of time travel (at least in the manner in which we consider it). The popular theory goes that if one were to travel back in time and alter one thing, then we could create a better world i.e. go back to the 1930s and stop Hitler, potentially saving millions. But the argument against that is that someone even worse may have come along in the aftermath of a non-Hitler 1930s or 1940s. There's the butterfly effect, best illustrated (IMO) in The Simpsons, which shows us just how one minute change can irrevocably alter the course of history. So with these concepts discredited (unless you believe in the idea of an infinite number of different timelines) time travel becomes harder to reconcile with what we know to be reality.

Now, there's the idea that you could go back in time and live your life in the exact same way, but because of the randomness you mention, surely even living the same way would result in a totally different outcome, because cause and effect is not linear, and every event that occurs 'randomly' in the way you describe would probably have an entirely different outcome, changing everything... no?

(I know nothing about physics BTW)

Dan, I think we should solve the snooker ball question first.

But could you travel back in time, win the lottery, then beat Hitler in a game of snooker?

Time travel is an interesting subject to think about -- quantum mechanics offers the 'many worlds' interpretation, which is a 'way of thinking' about quantum mechanics, not a physical prediction; and some people generalise this to a 'many timelines' story, which is pure science fiction, not testable even by thought experiment right now, because we simply don't know enough about quantum gravity!

Taking sci-fi ideas about time travel and adding in the stochastic influence of the time traveller absolutely does wreck any idea that they could 'stay quiet' and history would be unaltered, particularly over long time scales. Even just sending a rock back in time, to a place there was no rock before, a few hundred thousand years would doubtlessly have huge effects on what the 'new present day' looks like.

If you're looking for a more purely physics answer, we can make a few inferences from the mathematics of how spacetime is structured. General Relativity allows time travel if and only if the timeline is self-consistent: this is called the 'Novikov self-consistency principle.' You can't have something different happen on each 'loop': a self-consistent loop is called a 'closed timelike curve' if you want a term to Google. The gist is that you can't say "1" to your past self with the intent that they would say "2" to their past selves and so forth. You also can't send a rock back in time to a place where the rock wasn't before: the rock would have 'appeared there' already, and given it's there you'd have no choice about sending it. I and many other physicists infer that this ridiculous logical conclusion means time travel itself is impossible (or at least practically worthless, with wormholes turning anything entering them into entropy by converting them to pure heat energy: you might get to the past, but as a change in the wormhole's temperature, not as a whole human being!).

If Novikov exists and time travel is possible, it would be bad for free will: you would see yourself come out of the wormhole, and the Universe would have to somehow ensure that you did exactly what they did, even if you don't want to! It would be good for computation, however: schemes exist whereby you'd guess the answer to a computation, send it back in time, and have your past computer act in such a way that the timeline is only consistent if your guess was correct, meaning the Universe would have to ensure you guessed correctly! (IMO this is all nonsense. Not being forbidden by Relativity isn't the same as being really possible! Still, they are fun ideas.)

339 Dan.s until Christmas! wrote:This, then, I would think, is perhaps one of the strongest arguments against the concept of time travel (at least in the manner in which we consider it). The popular theory goes that if one were to travel back in time and alter one thing, then we could create a better world i.e. go back to the 1930s and stop Hitler, potentially saving millions. But the argument against that is that someone even worse may have come along in the aftermath of a non-Hitler 1930s or 1940s.

I gave up on becoming a time traveller when I realised that if I went back in time by even just one second I would reappear 242 miles away from the Earth and suffocate almost instantly.

I think if I could travel at light speed while going backwards in time at a rate of roughly 12m 50s per second I could keep up with the Earth.

Say I wanted to go back and experience the rise of the Beatles. I would aim for around this time in 1960, so I would need to sit in my time machine for about 26 and a half days, all the while navigating through space at light speed to make sure I kept up with the Earth.

Anything is possible... right?

I think most scifi explanations for the position problem tend to refer to target coordinates for your 'landing' to be relative to the start position, rather than the absolute position in a 3/4/12 dimensional universe.

Another cool thought experiment Ive seen is regarding free will down to the quantum scale. If a set of starting conditions are met and result in the quantum universe unfolding the same way every time then if you follow the chain up to the point wherein a mind is (a meat ball computing based on the potential energy of electrons in synapses) then how can there be any free will? The activity of the electrons is predetermined by the state of the underlying building blocks, so the logic follows that if they are predictable and unfold in a predictable manner, then what happens above them is unfolding in a predictable manner, and thus your thoughts are not your own, but a product of the conditions the brain is operating in. Its better explained elsewhere, but you get the point.

This can be extrapolated and applied to the many universe theory - where instead of the popular idea of if you choose either path A or B several potential universes are created where you choose one or the other or both or neither - simply the activity of the building blocks of the universe which your body is built from would also surely create alternative potential universes. What if one cell in your gut synthesises a protein in one scenario but fails to do so in another? What if the superposition of one quantum particle in one potential environment flipped rather than remained as is?

Many universes is a nice idea I think but untenable when taken down to the basics. But then again who knows what environment a universe exists in and whether it does or does not provide an acceptable medium for others to become.

Oblomov Boblomov wrote:I gave up on becoming a time traveller when I realised that if I went back in time by even just one second I would reappear 242 miles away from the Earth and suffocate almost instantly.

Why would you reappear 242 miles away from Earth? Is your method of time travel for some reason in the reference frame of the Sun? That's some odd time travel you have

Falsey wrote: rather than the absolute position in a 3/4/12 dimensional universe

What absolute position?

Oblomov Boblomov wrote:I gave up on becoming a time traveller when I realised that if I went back in time by even just one second I would reappear 242 miles away from the Earth and suffocate almost instantly.

I think if I could travel at light speed while going backwards in time at a rate of roughly 12m 50s per second I could keep up with the Earth.

Say I wanted to go back and experience the rise of the Beatles. I would aim for around this time in 1960, so I would need to sit in my time machine for about 26 and a half days, all the while navigating through space at light speed to make sure I kept up with the Earth.

Anything is possible... right?

I'm sure if you could figure out time travel then you could also figure out teleportation.

OrangeRakoon wrote:

Oblomov Boblomov wrote:I gave up on becoming a time traveller when I realised that if I went back in time by even just one second I would reappear 242 miles away from the Earth and suffocate almost instantly.

Why would you reappear 242 miles away from Earth? Is your method of time travel for some reason in the reference frame of the Sun? That's some odd time travel you have

Because, from what I understand, the Earth is moving through the universe at around 242 miles per second.

Moggy wrote:I'm sure if you could figure out time travel then you could also figure out teleportation.

I would never risk teleportation because I am convinced I would be destroyed and whatever appeared at the destination would merely be a copy!

Oblomov Boblomov wrote:

OrangeRakoon wrote:

Oblomov Boblomov wrote:I gave up on becoming a time traveller when I realised that if I went back in time by even just one second I would reappear 242 miles away from the Earth and suffocate almost instantly.

Why would you reappear 242 miles away from Earth? Is your method of time travel for some reason in the reference frame of the Sun? That's some odd time travel you have

Because, from what I understand, the Earth is moving through the universe at around 242 miles per second.

Moggy wrote:I'm sure if you could figure out time travel then you could also figure out teleportation.

I would never risk teleportation because I am convinced I would be destroyed and whatever appeared at the destination would merely be a copy!

But you'd risk going back to see Beatlemania and being ripped to pieces by your crazed 14 year old grandmother?

Oblomov Boblomov wrote:Because, from what I understand, the Earth is moving through the universe at around 242 miles per second.

This is incorrect - it suggests that there is an "absolute" frame or reference that we are comparing the Earth's speed against. This is intuitive because here on Earth we tend to measure things with an absolute speed, but that is actually just a speed relative to the "stationary" ground. If I was on a train going at 60 mph and I throw a ball forwards at 30 mph inside the carriage, is that ball going at 30 mph or at 90 mph? If you ask me, inside the carriage, I will tell you it is going at 30 mph. If you ask Alice who is standing on the embankment outside watching the train go past, she will tell you it is travelling at 90 mph. Alice isn't more correct than I am - we are both simply measuring the speed from different frames of reference. Speed is relative to the observer, and there is no single "absolute" frame of reference that is more correct than any other.

I believe the 242 miles per second figure is the speed of the Earth when compared against the Cosmic Microwave Background (CMB), which in fairness, if you want a value for the absolute speed of the Earth, is probably as close to a reasonable answer as you will get. This link might be useful

The theory of special relativity is based on the principle that there are no preferred reference frames. In other words, the whole of Einstein's theory rests on the assumption that physics works the same irrespective of what speed and direction you have. So the fact that there is a frame of reference in which there is no motion through the CMB would appear to violate special relativity!

However, the crucial assumption of Einstein's theory is not that there are no special frames, but that there are no special frames where the laws of physics are different. There clearly is a frame where the CMB is at rest, and so this is, in some sense, the rest frame of the Universe. But for doing any physics experiment, any other frame is as good as this one. So the only difference is that in the CMB rest frame you measure no velocity with respect to the CMB photons, but that does not imply any fundamental difference in the laws of physics.

(emphasis my own)

OrangeRakoon wrote:

Falsey wrote: rather than the absolute position in a 3/4/12 dimensional universe

What absolute position?

Exactly

I can totally get down with that way of thinking, however I am in no doubt whatsoever that if I travelled backward or forward in time the Earth would have left me behind by a considerable distance. The next thing you know, Matt le Blanc is attempting serious acting and there's a giant spider trying to kill you.

Moggy, it's not incest if you technically haven't been born yet. .

I'm not a physicist but I have read that people have been able to do something similar with roulette, but then there are a lot less variables. It't still not perfect but they were able to get a 17% return on their bets when normally you'd lose 2.7

http://www.forbes.com/sites/alexknapp/2 ... 0cea315217

Answer: no