Ask any question you want about Physics

Hey all,

Question for the physicists of ATS.

I heard on a documentary a few months ago from physicists the following:

'Anyone who says they understand Quantum Mechanics,
doesnt understand Quantum Mechanics.'

Is this correct?

Although we understand some aspects of QM, we dont know diddly sqat about about QM. But there are alot of theoretical models to describe QM.

Is the saying above correct?

Coomba98

originally posted by: coomba98
Hey all,

Question for the physicists of ATS.

I heard on a documentary a few months ago from physicists the following:

'Anyone who says they understand Quantum Mechanics,
doesnt understand Quantum Mechanics.'

Is this correct?

That quote looks like a variant of this quote from Richard Feynman, who won a Nobel prize for his understanding and advancement of quantum mechanics:

"I think I can safely say that nobody understands quantum mechanics." ~ Richard Feynman

Although we understand some aspects of QM, we dont know diddly sqat about about QM. But there are alot of theoretical models to describe QM.

Is the saying above correct?

Please read the opening post and watch the OP video since this is the topic, but no that is misstated because I wouldn't say there are a lot of theoretical models. The theoretical model is generally agreed on and works well at making predictions, so it's not a proliferation of models so much as a proliferation of interpretations of that model, such as the textbook Copenhagen interpretation which is probably wrong according to the OP video, the Debroglie-Bohm interpretation, The Everett interpretation, and others discussed in the OP video.

We have made some progress since Feynman's time in understanding some aspects of quantum mechanics, but the interpretation is still not settled.

a reply to: Arbitrageur

Arbitrageur,

Thanks for your reply informative as always.

When you say 'but the interpretation is still not settled.' do you mean that we know abit or even alot of QM interactions but we dont understand why these interactions are occuring.

Thats my question. How much do we know on why QM behaves as it does?

Would it be safe to say were still in the ancient Greek days of macro physics in regards to QM?

Coomba98

a reply to: coomba98
Speaking of the ancient Greeks, I'm reminded of the Ancient Greek Philosopher Plato and his Allegory of the Cave.

Plato has Socrates describe a gathering of people who have lived chained to the wall of a cave all of their lives, facing a blank wall. The people watch shadows projected on the wall from things passing in front of a fire behind them, and they begin to give names to these shadows. The shadows are as close as the prisoners get to viewing reality.

In the context of quantum mechanics I see the experimental results like the shadows on the wall, and our model is so good we can predict what those shadows will look like, but like the people in the cave who can only see the shadows we aren't sure what is causing them.

Take entanglement experiments for example. We can predict that a measurement on one entangled particle will result in a correlation with a measurement of the other entangled particle faster than the speed of light, but we don't really understands how this happens. There are several ideas on how it can happen which are consistent with experimental evidence, but we don't yet know how to prove which idea is correct.

a reply to: Arbitrageur

Arbitrageur.

Cheers for your response.

With regards to the observer creating micro and macro reality, would you say:

1. This is exactly what is happening; or
2. This is what appears to be happening but we dont understand anywhere near enough of QM to say this is what is happening.

Would number 1 be akin to saying the ancient Greeks concluding that lightning came from Zeus? Given the knowledge available at the time.

Coomba98

originally posted by: coomba98
a reply to: Arbitrageur

Arbitrageur.

Cheers for your response.

With regards to the observer creating micro and macro reality, would you say:

1. This is exactly what is happening; or
2. This is what appears to be happening but we dont understand anywhere near enough of QM to say this is what is happening.

Would number 1 be akin to saying the ancient Greeks concluding that lightning came from Zeus? Given the knowledge available at the time.

Coomba98

I would say if one uses the definition of "observer" that new-agers use, meaning it needs to be a human observer, none of the above is true. "Observe" as used by physicists means something different than how new-agers interpret the term. The observation doesn't require any human, nor any consciousness, merely an interaction with something else. An observation can be made by an inanimate object like a scientific measuring instrument in a room that is completely empty of any conscious beings.

This misunderstanding is all too common so I'll cite this source for further explanation:

Observer Effect

Q:There's a lot of confusion between the uncertainty principle and the observer effect, leading to the new age, nonsensical claim that we can willfully create the world around us by altering our thoughts. So, to be clear (because there's a lot of conflicting info out there), when we talk about "observing" an electron and thereby changing its state, we're talking about using equipment to measure it, not simply observing with the naked eye, right?

A: Right, we have no indication at all that interaction with conscious beings (e.g. us) does something different than interaction with any other large object in which some record is left of the results...

If just interacting with some inanimate large object is sufficient for a reality to be determined, is that what you're calling an "observer", the large inanimate object? I think there is endless confusion over this point with laymen who don't understand the context of "observation" in the scientific sense and thus mistakenly get the idea that a person must be the observer. This incorrect nonsense is quite prominent in the movie "What the bleep do we know".

a reply to: Arbitrageur

Cheers digger thats how i view it.

Thanks for the clarification.

Coomba98

Earth is oblique, is the Sun Spherical?

Is the axis of earth and the equator a straight line?

originally posted by: tikbalang
Earth is oblique, is the Sun Spherical?

Obliquity to the ecliptic of Earth: 23.45 deg, sun: 7.25 deg
Neither Earth nor sun is perfectly spherical but not too far off on a percentage basis.

Is the axis of earth and the equator a straight line?

I'm not sure what you're looking for here. While Earth's axis is a straight line, the straight line wobbles like a spinning top does in an effect called "precession", but because Earth is so much larger than a top, the precession cycles are much slower.

The equator looks like a straight line on a flat 2D map but of course except to members of the flat Earth society, the Earth is not flat so I wouldn't call it a straight line, it's an imaginary line that circles the Earth halfway between the North and South poles, and to circle the Earth, it has to follow the Earth's curvature.

a reply to: Arbitrageur

If i change the axis would the equator change?

a reply to: tikbalang
Yes, as the axis wobbles, the equator wobbles along with it, so that it's always halfway between the N and S poles. It takes about 26,000 years for this wobble (precession) to complete one cycle.

a reply to: Arbitrageur

what did it look like in 4000BC ?

a reply to: tikbalang
Run Stellarium, set the year to -4000, and you can see the alignment of the Earth for yourself better than I can describe it. Stellarium accounts for precession. Obviously Polaris (aka the "north star") wasn't aligned with Earth's axis at that time. This might help a little if you don't have Stellarium:

starchild.gsfc.nasa.gov...

At present, the star known as Polaris is the North Star. However, Polaris has not always been the North Star and will not always be the North Star. To understand that, we need to look at how the Earth spins on its axis.

a reply to: Arbitrageur

awesome thx!

a reply to: tikbalang
What's awesome, the NASA link or stellarium? You're welcome.

I saw the NASA link mentioned that in 3000 BC, the North star was a star called Thuban (also known as Alpha Draconis). I haven't checked to see if there was a North star in 4000 BC. Sometimes there isn't one, like now we don't have a "South Star".

a reply to: Arbitrageur

I used stellarium in the astronomy course, great program when doing research. One of the assignments was the northern star but I believe it was 40.000BC and then 40.000AD, I did the South Axis but it came up inconclusive in the Southern Hemisphere, however ancient times seems to have relied more on the horizon for all the s# they imagined.
There was a constellation in the southern axis but I forgot which

Arbitrageur, a really great thread! You are awesome!

I have a few questions. Answer whatever you are interested in talking about:

1. Why do electrons move at all?

2. Is time real? In other words, does the Universe execute the laws of physics in discrete steps or is all the energy in the Universe part of one single continuous wave of energy?

3. Is our Big Bang the result of a star collapsing to a black hole in another space-time dimension?

4. What is the source of energy causing the bright flash in this video to be as hot as the sun:

www.youtube.com...

5. If the expansion of the Universe is accelerating, will it ever stop?

6. Why is there any order in the Universe at all? Why do objects exist?

originally posted by: dfnj2015
Arbitrageur, a really great thread! You are awesome!

I pass your kudos on to the other contributors to this thread who have given some great answers, and I'm glad you like the thread.

I have a few questions. Answer whatever you are interested in talking about:

1. Why do electrons move at all?

Electric charge is "fundamental" meaning we don't have a deeper understanding of charge, but we do observe that electrons tend to accelerate in an electric field as a result of this fundamental property. Electrons inside the atom don't "move" as we understand the word "move", rather their behavior is unlike any common object we understand, but meshes more with our understanding of waves as discussed here: www.youtube.com...

2. Is time real? In other words, does the Universe execute the laws of physics in discrete steps or is all the energy in the Universe part of one single continuous wave of energy?

I agree with how John Baez has responded to this difficult question:

www.scientificamerican.com...

"The brief answer to this question is, 'Nobody knows.' Certainly there is no experimental evidence in favor of such a minimal unit. On the other hand, there is no evidence against it, except that we have not yet found it. There are no well-worked-out physics theories incorporating a fundamental unit of time, and there are substantial obstacles to doing so in a way that is compatible with the principles of General Relativity. Recent work on a theory of quantum gravity in which gravity is represented using loops in space suggests that there might be a way to do something roughly along these lines--not involving a minimum unit of time but rather a minimum amount of area for any two-dimensional surface, a minimum volume for any three-dimensional region in space and perhaps also a minimum 'hypervolume' for any four-dimensional region of space-time."

3. Is our Big Bang the result of a star collapsing to a black hole in another space-time dimension?

Nobody knows what came "before" the big bang, or if that question even makes any sense if time didn't even exist prior to the big bang.

4. What is the source of energy causing the bright flash in this video to be as hot as the sun:

It's not much energy, you probably create as much energy as that when you snap your fingers. What makes it amazing is the shrimp's ability to focus that energy into a volume with a diameter of maybe one millionth of a meter (which you can't do when you snap your fingers because you don't have any way to focus that sound into such a small volume). But the source of the energy is like snapping your fingers, it's just mechanical energy suddenly released creating sound and resulting cavitation, implosion of a tiny bubble, and sonoluminescence when the shrimp snaps its claw.

5. If the expansion of the Universe is accelerating, will it ever stop?

I don't think there's a definitive answer. It's conceivable that the current expansion and acceleration might be related somehow to the configuration of the universe and since we expect the configuration of the universe to change over time (eventually black hole domination and then black hole "evaporation"), the acceleration might not happen with alternate or future configurations. It's hard to see how anything will stop the acceleration in time frames which humans can begin to understand, like several times the present age of the universe.

6. Why is there any order in the Universe at all? Why do objects exist?

The universe has the behavior it does like order and objects because of the properties of our universe (the physical constant being what they are etc). We don't know why the properties of the universe are what they are, but if they were significantly different we might not have order or objects. (Some say if they were slightly different, but I'm not so sure about that).

Nima Arkani Hamed says this is a profound problem and he has studied it a lot more than I have so you might want to check out his videos on youtube to see what he has to say about it. I don't think he has any answers yet, but maybe he understands the problem better than I do, since he's obviously spent more time thinking about it. I tend to just accept that this is the universe that fate dealt us and accept it the way it is, but if someone can come up with a deeper understanding, that would be interesting.

originally posted by: dfnj2015

1. Why do electrons move at all?

They are being or were at one time accelerated by something, typically an electric field. Or they were instantiated with initial momentum greater than zero.

a reply to: dfnj2015

dfnj2015.

"2. Is time real? In other words, does the Universe execute the laws of physics in discrete steps or is all the energy in the Universe part of one single continuous wave of energy?"

I found this you tube clip to be fascinating. Only 10mins and explains in layman's terms what Einstein was thinking about time being an illusion.

youtu.be...

Coomba98