John Salerno

Not sure of the history/timeline. But Young's double slit experiment was very early - way before QM, in the 60s Jonsson performed it with electrons rather than light (or water waves etc) and caused a bit of a stir.

 

Uncertainty within our theories at the moment is not merely a measurement problem. Within the copenhagen interpretation of qm it comes from the fact that the matrices used to represent position and momentum do not commute - this implies the uncertainty, and it was later confirmed mathematically that uncertainty is necessary and the amount of this minimum amount of uncertainty was quantified . This is to say that it is deeply rooted within QM theory and is not merely an artefact of subs-standard measurement.

Hmm, very interesting. I know I need to read much more about QM than Hawking's brief summary, so that's a good start to get a sense of what it's saying. I need to find some other books for the general reader.

HUP does not merely state that we cannot simultaneously measure position and momentum, it holds that particles cannot have absolutely defined positions and momentum.

Ok, this was my main question. If it's the former, then determinism can still hold. If it's the latter, like you say it is, then I see how it undermines determinism. But does HUP really say that particles don't have defined positions and momentums? I thought it was just the principle that they can't be measured together.

I know that *later* QM has come up with the idea (after the two-slit experiment) that particles act like waves and thus really only have a "range" of possible positions, but is that really a part of the HUP itself? And even if it's true that a particle has a range of possibilities for position and momentum, isn't this still just a problem with our measurements, and not necessarily of the absolute position or momentum of the particle itself?

Everything is built from the atomic realm, so how could the classical realm be deterministic if the atomic realm isn't?

You don't seem to understand my point. I'm saying, just because a particle's position and velocity can't be measured accurately simultaneously, does that really mean that there still isn't an objective, determined position and velocity by which we could still theoretically determine past or future events. I.e., how does the uncertainty principle really undermine determinism?

I'm currently reading Stephen Hawking's book "A Briefer History of Time" and I was a little confused by the suggestion that the uncertainty principle undermines determinism, as stated in this sentence from the book:

The uncertainty principle signaled an end to Laplace's dream of a theory of science, a model of the universe that would be completely deterministic.

As explained in the book, the uncertainty principle states that the more accurately the position of a particle is measured, the less accurate the measurement will be of the particle's velocity. Therefore, the "initial conditions" of the system can never be accurately known in order to determine the past or future state of the universe.

This much is easy to understand, but it seems that the uncertainty principle really only undermines our ability to calculate these past or future states of the universe, not that it actually undermines the fact that the universe still is deterministic (not that it necessarily is, but the uncertainty principle as stated above doesn't seem to suggest otherwise), even if we can never calculate any given state of it because of this uncertainty.

However, I have seen elsewhere that perhaps the uncertainty principle suggests more than the simple explanation given in the book. That, in fact, it explicitly says that the position or velocity of a particle is not actually determined at all until it is measured. This seems to really hurt determinism, but is that really what the uncertainty principle says? That a particle's position or velocity essentially doesn't exist at all until we measure it, or is it simply that we can never know a particle's position or velocity for sure until the time of its measurement?

Basically, my question comes down to this: even given the uncertainty principle and the probabilistic nature of quantum mechanics, couldn't it still be the case that the universe is perfectly deterministic, even if we can't accurately make the measurements to determine these past or future states ourselves? Doesn't a particle still have a certain position and velocity at any given time, even if measuring one of these will then change the other?

Hawking hints at this idea:

We could still imagine that there is a set of laws that determine events completely for some supernatural being who, unlike us, could observe the present state of the universe without disturbing it. However, such models of our universe are not of much interest to us ordinary mortals.

Frankly, I think the mention of a "supernatural being" unnecessarily muddies the discussion and makes Hawking dismiss the idea too easily. It's not necessary to postulate anything supernatural in order to retain determinism.

The above quote could easily have been stated as something like this: "We could still imagine that there is a set of laws that determine events completely, despite our inability to measure the present state of the universe without disturbing it." Then the second sentence would be irrelevant, because it would be of interest to us to know that it is possible for the universe still to be perfectly deterministic, even if we can't (yet) discover all the laws.

Kinda rules out the book I was thinking of for QM. Have you considered reading the Feynmann lectures? Or watching them, there are sections on you tube I believe. He is great at providing explanations that are understandable and useful to people with pretty much any (or no) science background.

I've heard of those, but I assumed they leaned more toward QM rather than classical mechanics. I wanted to start with CM, then move on to relativity and then QM, sort of like reading a summary of the history of modern physics.

What's your maths level?

I like math but I'm no expert. Like I said, though, I'm looking for something aimed at a general audience, not something that requires prior advanced knowledge of any of the fields.

Hi everyone. I'm hoping someone can suggest a good book (or two) that gives a general but somewhat thorough summary of these two topics. I was considering reading The Elegant Universe, but I wasn't sure if I needed a better understanding of these two areas before moving on to string theory -- unless this book also introduces relativity and QM?

Otherwise, some other general introduction (aimed at non-scientists) would be great.

Thanks!

Sorry, I don´t know if one is more informative than the other- depends on whether you´re more interested in your maternal or paternal lineage, i guess.

Here´s an article on the subject of tracing human origins via mitochondrial DNA and Y chromosomal DNA testing :

http://www.ornl.gov/...migration.shtml

Thanks. I guess maybe it just doesn't matter, except for which side you want to trace.

Anyone have any thoughts? I'm thinking about using the mitochondrial DNA because that's the one that women *have* to use, so it seems that maybe it's more universal than using the Y chromosome method, if that even matters. I suppose either method would show similar migratory patterns in one's deep ancestry, and the divergence would occur more toward the end, depending on if your parents' ancestors are from different areas of the globe. Something like that?

I'm thinking about doing the National Geographic DNA test that traces your ancestry, and I was wondering if there are any good reasons to choose between the male and female line when you decide which path you want them to track. Is one more accurate than the other? What are the differences between the two?

Thanks.

Edit: Here's the description from the NG website:

We will test either your mitochondrial DNA, which is passed down each generation from mother to child and reveals your direct maternal ancestry; or your Y chromosome (males only), which is passed down from father to son and reveals your direct paternal ancestry.

I haven't read this book, but I read a similar book which is pretty helpful for being a dad: http://www.amazon.co.../ref=pd_sim_b_3

Since the book you found has been rated a little higher than the one I read, it seems you should go ahead to get it. Of course, I shouldn't be responsible if you didn't like it after the purchasing.

Actually I saw that one too, but I was a little turned off by this part of the review: "It is thick, detailed, and scientific." Maybe as a second book it will be good.

As for the rating, the book I mentioned has 5 stars with 14 reviews, your suggestion is 4.5 stars but with 161 reviews!

I'm interested in reading a book about how the mind of a young child develops, and I found this one on Amazon: http://www.amazon.com/Your-Childs-Growing-Mind-Development/dp/0767916158/ref=sr_1_2?s=books&ie=UTF8&qid=1314986650&sr=1-2

I was wondering if anyone could recommend this book, or some other book that is easily accessible (not a technical book or textbook) that discusses the subject of how a young child (anywhere from 1-10 years) grows, learns, reasons, understands things around him, etc.

I have to admit the description of the above book sounds perfect, but I wanted to ask here anyway.

Thanks,

John

Thanks! This stuff should be great! I'm actually looking forward to the experiments myself!

Thanks, those will be great to start with! Somehow when I do my own Amazon searches, I never seem to find these books in the lists!

I was wondering if any of you guys knew of any books that focus on the best ways to teach children about critical thinking, the scientific method, etc. Not books that focus on teaching specific things, or forcing your child to learn or memorize, but just a general kind for the best approaches to basically equipping a young child (4-5 years old) with the kind of mindset that will allow him to think, develop ideas and hypotheses, investigate things, etc.

I already do things like this with my nephew, so he can have a good foundation in critical thinking, but I didn't know if maybe there were other ways I can try, or games or experiments I could do to show him these things in action.

Thanks.

Thanks very much! Any comment on the question about pneumonia? I know that it's a virus (or bacteria?) too, and thus can't be directly caused by having wet hair in cold weather, but is there any connection at all? Is it the same answer as you gave for other colds, i.e. wet hair (or skin) causes you to be chilled in cold weather, and thus increases the chances of catching pneumonia?

There is a difference, sweating skin is also cooled by evaporation, and the fan helps that too.

So in the case of a dog, heat doesn't leave the surface of their bodies in the same way as humans (via evaporating sweat) but it still can be borne away from their bodies by cool surfaces and cool air...is that correct? I was thinking that heat only left their bodies through their tongues or feet, so that's why I didn't quite see how a cool floor or fan could help them lose heat.

Ever walked across a lino floor with bare feet on a cool day?

The floor is cooler than your feet so it conducts heat away from them and that makes your feet cooler. The carpet isn't as good at conducting heat so it doesn't work so well.

Similarly the air is usually cooler than you (or your dog) and carries away heat. The fan makes that process work better because more air hits you and more air can carry more heat.

 

If the air is warmer than the dog's body temperature (typically 38 to 40 C) this won't work. It will have to lose heat by panting.

Thanks. I just wasn't sure if those things worked differently for dogs since humans have perspiring skin and dogs don't.

I've read that dogs have sweat glands only on their tongues and the pads of their feet. So I was curious about two things I've noticed my dog (and some other dogs do):

1. When they are hot, they tend to lie on the floor instead of the carpet. Does lying on linoleum, hard wood, etc. keep them cooler? Maybe this case has nothing to do with sweating.

2. They also lie in front of a floor fan we have. This is what confused me because as far as I know, the reason fans cool off humans is because it evaporates the sweat on our skin. Since this doesn't happen for dogs, do they actually gain anything from lying in front of a fan when they're hot?

Thanks.

My wife gets ear aches from cold wind all the time. If it is below about 40 (F) and windy she must have her ears covered or she'll get a temporary ear ache. Since both infections and wind (for some people) can cause pain, I imagine it wasn't too big a leap for some to assume that the wind was causing infections.

With cold wind that's understandable, since it can even make your skin numb or hurt. But I had in mind just the wind itself, not the temperature. So let's say a windy day at 80-90 degrees F. That's what I'm thinking about, so that the cold is not a factor, just the actual wind itself.

If there has ever been an ear or sinus infection, there could be a chronic, subclinical or asymptomatic, underlying infection that can be exacerbated or "flare up" in cold, wet, or windy conditions. This could easily be interpreted as a "new" infection resulting from the exposure to adverse conditions. ...I have an ear that must be protected from wind--even cold gentle wind or warm high wind--to prevent pain and fluid buildup that is noticable upon leaving those conditions.

 

But I agree that it is a myth that those conditions cause a disease. At most, those conditions allow some underlying or impending affliction to manifest itself; or it might have been otherwise unnoticed or healed without the stress of those adverse conditions.

~

So the wind itself can't cause any *new* problems? What about simply causing an ear ache? I'm just trying to figure out if that's even medically possible.

Can someone explain to me (in layman terms, mostly) what "b", "p", and "beta" stand for in Table 2 in this article:

http://www.plosone.o...al.pone.0017006

Also, I have trouble reading parts of the Tables (especially Table 2) because I don't have any sense of what "units" are being used for these values. In Table 1, mL is specified in one case, so that makes sense. In other sections it's simply the number of people in the study, but how do you read the numbers that don't have units, like the "Stress" or "Social support" values, or anything in Table 2?

Thanks.

But can anyone just address the simpler question of whether latex condoms have naturally occurring holes? The study cited above (from thedavidbjorn) seems like it was meant to investigate this, but the results don't necessarily suggest that the virus penetration was a result of naturally occurring holes.

John S; There are literally thousands of books related to both the Religion and the plight of those in the religion to form a Jewish State, known as Zionism. I am neither Jewish or in fact religious, but have read some, as you seem to be, interested in the subject from both a historical and political perspective. The link offered, is free and gives references to other books. Good Luck....

 

 

 

http://ebookee.org/I...ive_197097.html

Ooh thanks, that book sounds like a great start!

Can anyone recommend a good book that details the founding of Israel and covers all of the major events that have happened since then that have formed the Israel/Palestine conflict? I'd love to learn more details of things like the country's founding, the borders and how/why they've changed over the century, the arguments on both sides for and against a Jewish state, etc.

Thanks!