Darkness

Dirac on Theoretical Physics

Here's a video clip of Paul A.M. Dirac explaining how theoretical physicists worked -- or, at least, how HE worked:

 

He was British, and his full name was Paul Adrien Maurice Dirac. I'm surprised I still remember that.

The Schrodinger equation wasn't consistent with Einstein's special relativity. Among other things, it got the spin of the electron wrong. (In fact, Schrodinger didn't include spin at all.)

Dirac derived the relativistic Schrodinger equation, consistent with Einstein, and, miraculously, it correctly predicted the spin of the electron (within a few percent; quantum electrodynamics--the field theory of relativistic quantum mechanics--would do the rest). Here's what Dirac's equation looked like:

That's kind of messy, though the Wiki page explains it. Psi is the usual wave function of quantum mechanics, although in Dirac's theory it's a 4-dimensionl vector. (In Schrodinger it's just a regular function over all of space and time, what physicists call a "scalar.") But my generation, and the one before, and those following know it as:

It's just mathematically simpler. Moreover, now we set c=1 (the speed of light), and, for that matter, G=hbar=k=1, where G is Newton's gravitational constant, hbar is Planck's constant divided by 2*pi, and k is Boltzmann's constant. These constants simply set the scale of dimensions, and can always be added back if you're looking for real-world predictions.

{If you're said it will take you "an hour" (or whatever) to drive from home to you grandma's, you did the same thing with units, taking your velocity to be =1.}

I don't think I've ever solved the Dirac equation except for a free electron, as has every other graduate student in physics, but I once saw a PhD dissertation that solved it for the hydrogen atom. It was nontrivial.)

Anyway...when he was a young physicist in Europe, Dirac derived his equation from general considerations, a real tour-de-force of both quantum mechanics, special relativity and mathematics for its time. It was better than Schrodinger.

Dirac was a little weird, no doubt an advantage:

His colleagues in Cambridge jokingly defined a unit called a "dirac", which was one word per hour.

This likely contributed to his great success. Dirac put forth his equation in 1928, and by 1933 won the Nobel Prize in physics, along with Schrodinger. Dirac has just turned 32 years old.

Wiki:

"After having relocated to Florida to be near his elder daughter, Mary, Dirac spent his last fourteen years of both life and physics research at the University of Miami in Coral Gables, Florida, and Florida State University in Tallahassee, Florida."

Dirac did other notable work besides his relativistic wave equation, but nothing on its scale, and it's what he will forever be known for. 

So I found it really interesting to watch him talk about what made him tick.   

An Unexpected iPhone Issue

I found an unexpected...issue...with iPhone's Siri when I asked it to do a calculation: It doesn't understand scientific notation. 

I wanted to know the ratio of the mass of Jupiter to the mass of the Earth, so I asked Siri to calculate it. I gave it instrutions:

"Hey Siri, divide one point nine times ten to the twenty-seventh by five point nine seven times ten to the twenty-fourth."

It returned 3.18 x 10⁵⁰, when the correct answer is 318.

It took me a minute to figure out that the calculation it did was

(1.9)*(10²⁷)÷(5.97)*(10²⁴)

which gives 0.31825 x 10⁵¹, which after adjusting the decimal point is the number it gave.

 
Siri treated multiplication and division equally, on the same level. It doesn't understand scientific notation. I really didn't expect that. But maybe I should have.

Nor does it understand a number in the form "one point nine e twenty-seven". She doesn't understand the "e".

It also gives the wrong answer, albeit a different answer, if you rotate the iPhone to the screen with the advanced functions and speak to it. 

For some reason it now took "e 27" to be 10^{20/7}, but got "e 24" correct as 10²⁴.

Now I know. But I hope someone on a project team, when rushing during a dire crisis, doesn't use Siri to calculate a rocket trajectory or whatnot.  

Good Bones

By Maggie Smith 

"Life is short, though I keep this from my children.
Life is short, and I’ve shortened mine
in a thousand delicious, ill-advised ways,
a thousand deliciously ill-advised ways
I’ll keep from my children. The world is at least
fifty percent terrible, and that’s a conservative
estimate, though I keep this from my children.
For every bird there is a stone thrown at a bird.
For every loved child, a child broken, bagged,
sunk in a lake. Life is short and the world
is at least half terrible, and for every kind
stranger, there is one who would break you,
though I keep this from my children. I am trying
to sell them the world. Any decent realtor,
walking you through a real shithole, chirps on
about good bones: This place could be beautiful,
right? You could make this place beautiful."

Via the Poetry Foundation

Warning About Blogging

Blogger was abandoned by Google a few years ago, and lately it's been getting worse and worse. A lot of problems. It's becoming so bad it may have to be abandoned soon. Just much more trouble than solution.

I'm not going to try to port all this to, I guess, Wordpress. Too much hassle, if it worked even a bit.

I don't have the enthusiasm anymore anyhow.

Bradbury Quote

“You don’t have to burn books to destroy a culture. Just get people to stop reading them.”

Ray Bradbury

I don't think he wrote this in his book Fahrenheit 451. I guess perhaps in an interview about it.

I just read 451°F two years ago. Never read it when I was younger, or was made to. Should have been much earlier. A good book that ended in a way I hadn't anticipated.

Did you know he wrote this book in 9 days? On a typewriter he rented by the hour at a local university?

Where US Coastal Land is Sinking

-4 to -6 mm/yr in a few places. Some less all across the Gulf Coast, and in many places along the Atlantic coast.

      

Source: 

CNN, 06 March 2024. 

https://www.cnn.com/2024/03/06/climate/sinking-cities-us-sea-level-rise-climate/index.html