silliness

Both Roads Taken

drorzel — Mon, 09 Mar 2015 08:10:10 +0000

Both Roads Taken

Two roads diverged in a yellow wood,
And caused me no small amount of panic
For traveling both of them would be good
But there simply was no way I could
Until I remembered quantum mechanics.

So half my wavefunction I sent left
And rightward steered the other half
Both pieces of me with equal heft
And thanks to calculations deft,
I knew the end would sum both paths

Plenty of physicists claim to know
Or at least will confidently speculate
That collapse, or a pilot wave's flow,
Or decoherence act to make it so.
Me, I just shut up and calculate.

So in the woods I went two ways
To return together some distance hence
And through the passing of many days
My branches accumulated differential phase
Which in the end makes interference.

With apologies to the estate of Robert Frost. Credit and/or blame for inspiring this silliness goes to this Stephen Curry tweet.

drorzel Mon, 03/09/2015 - 04:10

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Culture

humanities

Physics

Pop Culture

Excellent! I'm going to send EVERYONE here to read this.

Plus: in high school, we sang a choral version of the Frost poem. So, I cannot read your poem without singing it in my head...

The Yannkee great Babe Ruth must have a quantum intution, when he said
"when you come to a fork in the road, take it"

Wasn't that Yogi Berra?

Yes, that one is a Yogi Berra quote.

Berra definitely had some kind of quantum intuition, because he also came up with these gems:
-You can observe a lot just by watching.
-You've got to be very careful if you don't know where you are going, because you might not get there.
-I wish I had an answer to that because I'm tired of answering that question.
-The future ain't what it used to be.
-Nobody goes there anymore. It's too crowded.

*blink* *blink* Oilcan? Wow. Long time.

It was Yogi Berra, and it made sense because the fork in the road was actually the two ends of a loop road. So you got to his house no matter which fork you took.

If you know this, the "To return together some distance hence" line will be even more appropriate.

How Not to Control the Weather for Your Dog

drorzel — Tue, 24 Feb 2015 09:06:26 +0000

How Not to Control the Weather for Your Dog

I'm rooting around in my bag for a pen, and pull out a laser pointer by mistake. Since I'd really prefer not to be grading, I flip it on and shine it on the floor next to the spot where Emmy is half-dozing. She immediately leaps up (she's pretty spry for a dog of 12...), and pounces on it. Or tries to, as I flick the spot across the room.

"Get the dot! Get the dot! Getthedotgetthedotgetthedot!" she mutters as I lead her on a lively chase around the room. After a few minutes, I click the laser off, and put it down. Emmy comes over, panting, and I scratch behind her ears.

"That was fun, eh, girl?" I say.

"Important, too!" she says brightly.

"Important... how?"

"I'm helping fix the weather!"

"Ummm... How does chasing my laser pointer spot around the room help fix the weather?"

"Well, you remember how cold it was on our walk this morning, right? When I got that nasty squeaky snow between my toes, and you had to rub it out? And you said 'I am so sick of this stupid winter...' Only, you know, with some extra bad words mixed in."

"Yeah..."

"Well, you talk about all these physicists who do laser cooling, and how cold they make stuff, and it's super cold outside, so I figure it must be all those lasers. And if I can take a few of them out, maybe it will warm up enough for the bunnies to come back out in the yard so I can chase them!" She wags her tail proudly.

I sigh. "OK, I don't quite know where to start with this... First of all, the amount of stuff you can cool with lasers is really tiny."

"Sure, but even a small amount of stuff makes a difference if it's cold enough. I mean, when you drop an ice cube into my water dish, that cools off all the water. And these laser things are a whole lot colder than an ice cube, right?"

"Well, yeah-- an ice cube is usually right around freezing, or 273 Kelvin, while laser-cooled atoms are at a temperature of a few millionths of a Kelvin. But a really big laser-cooled sample might run to a hundred billion atoms."

"And that's a lot!"

"Not if you're talking about atoms. An ice cube contains, let's see... probably about 10²³ molecules of water. That's a trillion times as many atoms as a really big laser-cooled sample."

"Oh. But there are lots of people doing laser cooling these days, so maybe all of them working together..."

"No. There aren't a trillion people in the world, let alone a trillion research groups doing laser cooling."

"Oh."

"And anyway, laser cooled samples are always contained in ultra-high vacuum chambers. You remember the big metal chamber from the time we visited my lab for that photo shoot, right? They're inside that, not out where they could cool anything else."

Me and Emmy with some of the laser cooling apparatus in my lab.

"Why is that?"

"Well, because laser cooling only works for very specific atoms and molecules. You need to have a laser that's tuned close to but a little bit below one of the frequencies of light that the atoms like to absorb. Then atoms moving toward the laser will see it Doppler shifted--"

"Eeeeeeee-ooooowwwwwww!" Emmy makes a race car noise. I kind of wish I had never used that example with her.

"Yes, exactly. The atoms moving toward the laser see the frequency shifted up, closer to what they want to absorb. And when they absorb a photon from the laser, they get a kick in the direction it was headed, which makes them slow down."

"Like bouncing a little ball off a big ball!"

"Right."

"And then you get to chase both balls!"

"Try to focus, please. Atoms moving toward the laser slow down, but atoms moving away see the laser shift even farther from their natural resonance frequency, and so aren't affected at all. Which is why you can use laser beams to slow specific atoms. But it only works for those atoms, which is why we do laser cooling experiments in the middle of ultra-high-vacuum chambers, so they don't collide with other atoms and heat back up."

"OK, but couldn't you just, like, keep cooling them down? So, you know, when the other atoms from the air hit the laser-cooled atoms, they get a little bit colder, and if you keep doing that, eventually the air gets cold even though it doesn't interact with the lasers?"

"That's a good idea," I say, and she wags her tail. I scratch her favorite spot just behind her ears. "That's a real thing that people do, called 'sympathetic cooling,' and it's a big part of some experiments. Sometimes, you can't effectively cool one type of atoms with convenient lasers, so instead you mix those together with another kind of atom that you can laser cool, and cool your target atoms indirectly."

"Which lets you use laser cooling to control the weather!"

"Um, no. Even sympathetic cooling experiments are done under vacuum. It's the same problem as with the ice cube-- the number of atoms you can effectively laser cool is too small to affect the vastly greater number of atoms in air."

"Well, what if you got a really big laser?"

"You could cool more atoms with more laser power, but you're not going to get a trillion times bigger that way. And, anyway, if you tried to do that, the laser power supply would generate so much waste heat that you'd end up making the weather warmer, not colder."

"Oh, right. The second law of thermodynamics."

"Exactly." (I know better than to ask how she knows about that...)

"Stupid entropy..."

"Um, yeah. Anyway, laser cooling is not responsible for the frigid weather, so you're not actually doing important work by chasing the laser-pointer spot around the room."

"OK, maybe it's not fixing the weather, but it is important."

"Important, how?"

"Well, you're getting a blog post out of this, right?" She looks insufferably smug.

"You're a very clever dog," I say.

"So can I chase the spot some more?"

"After I type this up, sure."

"Yippee!!!"

-----------

(If you're new here, and enjoy this, let me note that I have two books full of talking-dog physics: How to Teach [Quantum] Physics to Your Dog and How to Teach Relativity to Your Dog; there are also more talking-dog physics blog posts. I've also got a new book, albeit not with Emmy, about how you think like a scientist without even realizing it, which isn't directly relevant to this post, but is awesome in its own right...)

drorzel Tue, 02/24/2015 - 04:06

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Yay Emmy!

I really must remembering to read this. It's cute, odd, and by the sounds of it, quite smart.

Ernest, the Purple Aardvark

drorzel — Fri, 26 Dec 2014 05:12:26 +0000

Ernest, the Purple Aardvark

Ernest, the purple aardvark
Had a long and hairy nose
And if you ever saw it,
You would really say "Boy I bet you could eat some ants with that thing..."

All of the ants in Tasmania
Use to run away when they saw him
Because if they ran to slowly,
[Loud slurping noise] Ernest ate them up.

Then one foggy Christmas Eve,
Santa came to say,
"Ernest, we have a terrible infestation of termites at the North Pole,
Can you come eat them up while I deliver toys to good boys and girls?"

Then how the elves they loved him,
And they knitted him warm nose cozies
Because aardvarks normally live in tropical climates
And they're not used to the North Pole.

Ernest, the purple aardvark,
You'll go down in hiiissss-toooorrrr-yyyyyyyyyy!

Improvised last night for The Pip's entertainment, transcribed here because Kate mentioned it on social media. I blame Dante Shepherd for this. Also, there may have been wine.

drorzel Fri, 12/26/2014 - 00:12

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personal

silliness

The Pip

Conceptual Physics Halloween Costumes 2014

drorzel — Wed, 29 Oct 2014 08:03:31 +0000

Conceptual Physics Halloween Costumes 2014

A fine if somewhat intermittent tradition hereabouts has been the offering of high-concept Halloween costumes for people interested in physics, surfacing in 2010, 2012, and 2013. I'm a little too fried right now to do anything all that deep, but I'll try to offer a few suggestions; see also these particle-physics suggestions from Symmetry magazine, who have an art staff to make animated GIFs of their ideas.

Sexy Tycho Brahe: Ruffled collar, magnificent mustache, a little gold paint on your nose. Critically important that you remember to go to the bathroom beforehand, though-- it's going to be a long party.

The Principle of Least Action: Dress like Pierre de Fermat, and remain perfectly still unless you have somewhere to go. When moving from one point to another, carefully plot out the shortest possible path, and sprint along it as fast as you can.

The Holographic Principle: Stick very close to the walls of the room, but watch everything carefully, so as to ensure you contain all of the information about what's happening in the interior of the party.

Sexy Dmitrii Mendeleev: Dress like Radagast in the Hobbit movies. Try to get the other guests to line up in order of weight.

Particle-Wave Duality: When nobody's looking at you, go from place to place in the most wave-like manner possible, say by doing the worm. If you catch anybody looking, stop immediately and walk like a normal person.

The Equivalence Principle: Climb on top of some tall object, jump off, and loudly insist that gravity has stopped working as you fall.

Sexy Arthur Eddington: Round glasses, suit and tie. Publicly humiliate a companion dressed as Sexy Chandrasekhar, then natter on about the fine structure constant for the rest of the party.

And that's about enough of that for this year. Feel free to throw out your own high-concept costume ideas in the comments.

drorzel Wed, 10/29/2014 - 04:03

Tags

Currently working on the Theory of Cosmic Inflation costume. I plan on eating something 7/1000ths of my body volume about every 15 minutes during the course of the party to match the rate of cosmic inflation if it were slowed down by a factor of one in a hundred million trillion trillion trillion.

One Does Not Simply Science Into Mordor

drorzel — Mon, 13 Oct 2014 06:27:46 +0000

One Does Not Simply Science Into Mordor

I recently shot a bunch of video of myself in front of a green screen, for something that will be revealed in due time. Of course, if you have green-screen footage of yourself, you're pretty much obliged to do something silly with it, so here's a quick GIMP-ing of a still from the video (also visible as the "featured image" above...).

One does not simply science into Mordor

(I was going to try to put myself inside Mount Doom holding a Ring, but I couldn't find a suitable background image, and I've already spent too much time on this silliness. It's not the classic Boromir pose, but it'll do.)

I realize this is highly risky, the Internet being what it is, but if you think you can do better, here's the original image:

Me in front of a green screen making a dramatic gesture.

I have another image with good photoshop potential, but we'll see if this one produces anything entertaining first...

drorzel Mon, 10/13/2014 - 02:27

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personal

Pictures

silliness

Entrance Music

drorzel — Mon, 22 Sep 2014 07:01:09 +0000

Entrance Music

The AV Club had a Q&A last week asking "What would be your entrance music?" As a music fan and a sports junkie this is, of course, a nearly irresistable question, though a lot of other things got in the way before I could get around to typing up an answer.

I've always kind of thought that Superchunk's "Hyper Enough" would be fantastic entrance music for somebody:

Of course, that somebody wouldn't really be me, as I'm not especially hyper. If I were going to be running out onto a stadium floor for some sporting purpose, I would need something more in line with my actual speed. Maybe a little Sugar:

That's a pace I could actually maintain. Of course, it's also twenty-odd years old, so perhaps something more contemporary in a similar tempo, off the new Afghan Whigs record:

Then again, that one sounds maybe a little too much like stripper music, which is not an image anyone needs. So we could go to my current favorite band in the world, the Hold Steady, whose latest album makes a big entrance:

Though again, maybe a little more uptempo than my size and footspeed can justify. And, of course, the subject matter maybe isn't the most family-sporting-event-friendly...

But then, really, it's kind of an act of colossal vanity to imagine myself needing entrance music in a sporting context. Which then leads to idly pondering entrance music in an academic context, and what might work for that.

Academic entrance music, of course, would probably demand a greater lyrical density, so something like the Weakerthans, maybe:

A little mellower, but a catchy song, and sort of thematically appropriate, given the way a lot of intro physics involves rethinking ordinary situations.

But then, this term, I'm teaching a Gen Ed class on relativity, so perhaps this might be more appropriate, as a realistic analogy for what the class will accomplish:

It sounds awfully cool, but when you really try to follow what's going on, it ends up as gibberish.

But, really, I'm not a tenth cool enough to pull that off, even ironically. Anyway, as an academic currently serving as department chair, there's really only one choice: song number three from John's last CD:

That's one of those songs that's absurdly personal and specific, and on paper seems like it shouldn't work at all. But it's brilliant, and works in almost any circumstances where you need a kick to keep going. I listened to that one a bunch when I was up for tenure, too.

At any rate, while it's not really a definitive answer to the original question, that's at least a bunch of excellent music to get you through your Monday morning. Feel free to suggest others in the comments; I don't know if embed code will work there, and links may get held for moderation, but I'll clear comments when I get the chance.

drorzel Mon, 09/22/2014 - 03:01

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Very classic :) I guess I'd either go for 'No one knows' https://www.youtube.com/watch?v=HHpxk8zwv6Y
or 'Supermassive Black Hole' https://www.youtube.com/watch?v=0LgcDpTH47g

"Supermassive Black Hole" is an excellent choice. I wish I knew enough GR to justify using it.

If only the opening of "Seven Nation Army" were longer or the opening verse thematically appropriate past the first two lines, I'd love to stalk out onto something-or-other to it. http://www.youtube.com/watch?v=0J2QdDbelmY

"Supermassive Black Hole" also excellent, or -- though this is probably terribly over-used -- I still fondly remember walking out of _The Matrix_ into a sunny afternoon, putting on my sunglasses, and pretending I was wearing a long black leather coat as I walked up Huntington Ave., so that: http://youtu.be/aTL4qIIxg8A?t=51s .

In a purely sports context, there's a case to be made for "On with the Business" https://www.youtube.com/watch?v=eIOgfFm27K8 because of the bit where Craig Finn yells "Let's get on with the business!" over the opening chords. That's a very pro-wrestling-intro kind of moment. The rest of the song is sub-optimal for those purposes, though.

"The House that Heaven Built" also kicks off really well https://www.youtube.com/watch?v=TRVCtbfuDqw and has that "Oh oh oh oh oh-oh oh oh!" shout-along chorus a little bit into it. Again, probably too fast for me, but an awesome song.

when you really try to follow what’s going on, it ends up as gibberish

That's probably the case for a lot of entrance music with lyrics. If the lyrics aren't just right for the situation, you are likely to get a WTF reaction from a large fraction of your audience.

The scherzo movement from Beethoven's Ninth Symphony is one classic that works for a number of situations. If you remember Keith Olbermann's Countdown show on MSNBC, you will recognize the opening bars as the theme from this show. Keep going if you want to portray yourself as working frenetically--that's the point of a scherzo.

If you are looking for something a bit more modern, then try The Piano Guys' version of David Guetta's "Titanium" www.youtube.com/watch?v=fz4MzJTeL0c which lets you start calmly and build up the intensity as you come in.

If you interpret the first part of The Afghan Whigs as the heavy deliberate footfalls of a big guy striding into a classroom ... sounds about right! Entrance music doesn't have to be the entire song, or lyrical. That would be perfect for walking down the center aisle of a big lecture hall. It would certainly quiet down the room!

I've often joked about using entrance music for periods where I'm walking in with a stack of exams for my students. In that situation, the choice is clear: 'The Imperial March' by John Williams.

The Real Pi Day(s)

drorzel — Fri, 14 Mar 2014 08:53:10 +0000

The Real Pi Day(s)

Today is March 14th, 3/14 in the normal American way of writing dates, so you'll find a lot of silliness on the web today talking about "π Day" due to the coincidental similarity with the first three digits of π (see, for example, Rhett's annual post). But, of course, this is an archaic and local convention, and not really suited to the dignity of science.

After all, the defined SI unit of time is the second, so if you're going to do things properly, you really ought to measure time in seconds (like the Qeng Ho in Vernor Vinge's brilliant A Deepness in the Sky). So, a proper celebration of the number π should fall at some power-of-ten multiple of 3.141592653589793238... There are eight of these in a calendar year (there are 31,556,736 seconds in a year, give or take), but none of them are in March.

1π s - This obviously occurs a bit after midnight on January 1, possibly before you finish saying "Happy New Year." Assuming you're young enough and your kids are old enough for you to be happy about being up at that hour on that date.
10π s - This is half a minute after midnight on January 1, around the point you're wondering "What the hell is a Lang Syne, and why would I want an old one?"
100π s - Just past 12:05 on January 1, maybe a good time for a silent tribute to the world's most famous transcendental number.
1000π s - A little bit after 12:52 on January 1. Pour an offering of flat champagne into a round glass as tribute.
10,000π s - 8:43am on January 1. If you're awake, celebrate by sweeping party trash from the first four celebrations into a trash can with a circular cross-section.
100,000π s - Around 3:16pm on January 4. The first time you could reasonably throw a "π Party" without the celebration being subsumed in another holiday.
1,000,000π s - About 8:40 am on February 6. This would be a really good time for a party-- it's well clear of anything else, and a time of year when people really need a pick-me-up.
10,000,000π s - 2:38 pm on December 29 (or 28, in a leap year). This has gone so far around that it's caught up to the winter holidays again. If you want to ostentatiously reject Christianity and all its offshoots, but still get festive in late December, this would be a good excuse.

So, there you go: if you want to properly celebrate the ratio between the circumference of a circle and its diameter, those are the correct times for your observances. None of this mid-March silliness, please. Unless you're one of those heretics who prefers τ to π, in which case, the appropriate dates are all multiplied by a factor of 2, and the proper celebration of 1,000,000τ s is on... March 14 at 5:19 pm (in a non-leap year). Hmmm...

drorzel Fri, 03/14/2014 - 04:53

Tags

U.S. date conventions aren't much more arbitrary or silly than base 10. I am having some trouble choosing a specific alternative, however.

I was thinking about this earlier, and to make the date actually look like pi you either have to use the European (in my experience) convention of using a period but the American convention of month/day (3.14) OR the American '/' and European day/month in July (22/7). In my, admittedly limited, experience relatively few people would actual be writing any date as pi. Besides 2pi is a much better day - it's my birthday.

And you didn't mention that one year contains about pi*10^7 seconds? What is wrong with you?

Set your clocks now for March 14 2015 at 9:26:53.

Snow Plow Projectile Physics

drorzel — Fri, 14 Feb 2014 07:37:03 +0000

Snow Plow Projectile Physics

We got over a foot of snow yesterday and today, so schools are closed. Except Union is a residential college, so we never close, which means I have to dig my car out all the same. Which I did, clearing a path to the unplowed street, then took Emmy for her morning walk. During which, of course, the town snow plows came around and filled in the end of our driveway again...

As I was digging out again, I was struck by just how far the snow had gone up the driveway-- I paced off about six meters from the edge of the road to the farthest clumps thrown up the driveway. As a way to distract myself from being pissed about the extra work, I started thinking about whether you could use this to determine the speed of the plow.

It might seem that there isn't enough information here, but as always, we're really just interested in order-of-magnitude sorts of numbers, here. Well, probably better than that-- maybe a factor of two or so. But nothing hyper-exact.

So, given that, we can approximate our driveway as flat, with snow taking off from and returning to ground level. In that case, there's a really simple formula to give you the range of a projectile launched at some angle, provided you neglect air resistance. That's not a great approximation for snow in general, but there were some good-sized lumps in there, so it's probably not a huge factor. And again, factor of two numbers, here. So, we have the projectile range formula:

$latex d = \frac{v^2 \sin (2 \theta )}{g} $

That requires an angle, so you might think it's hopeless, but what we care about is the farthest lumps of snow, so we can just go for the maximum value, at a launch angle of 45 degrees. There must be some snow thrown at that angle, given the wide range of spray from a moving plow, and that is presumably the stuff that goes the farthest.

With a distance of 6m and an acceleration of 10 m/s/s, that gives a launch speed of just under 8 m/s, which we'll round up, because air resistance will tend to shorten the range, so that's the direction in which to err.

So how does that speed relate to the speed of the plow? Well, the plow is barrelling down the street at some speed, with a blade in front of it at some angle, so stuff on the left edge of the blade gets pushed right, toward the shoulder of the road and the clear end of my driveway. The speed at which stuff moves across the road-- which is what will determine how far it goes up the driveway-- is probably something like the speed of the plow times the sine of the angle the plow makes with the front of the truck. They generally go by pretty fast, and the angle is adjustable, so this is kind of hard to gauge, but I'll pick a nice, friendly number like 30 degrees. In that case, the sine is equal to a half, and the speed of the plow would be twice the speed of the snow, or about 16 m/s.

Converting to units for which I have some intuitive feel, that's about 35mph. Which is technically faster than the speed limit in our neighborhood, but not out of line for the speed people actually drive down our street. And the plows certainly go by at a pretty good clip-- not that you can blame them, given the number of streets they have to clear.

So, there you go: the math I did in my head while digging the end of my driveway out for a second time. Which is the physicist's version of "Serenity now!!!!"

drorzel Fri, 02/14/2014 - 02:37

Tags

Sounds about right; speeding snow plows sure can kick up a storm...did you see the viral video of the snowplow knocking over the guy in NY?

http://www.nydailynews.com/new-york/brooklyn/brooklyn-man-smashed-snow-…

"God, grant me the serenity to accept the things I cannot change,
The courage to change the things I can,
And the wisdom to make a Fermi problem out of both."

As you can clearly see that some snow is moving forward of the plow, the actual speed of the snow must exceed the speed of the plow. In theory it can have an entirely elastic collision with the plow blade and bounce away at twice the speed of the plow. This puts a lower limit (assuming everything else is the same) of 8 m/s (18 mph) for the plow.

Much depends on the type of snow plow, by which I mean the design of the blade itself.

Standard plows have the top edge parallel to the bottom edge, and a uniform curvature across their entire width, which is a section of a cylinder if viewed from the side. These have to be operated at a steep angle relative to the direction of travel, for example 45 degrees, to prevent snow spilling off the leading edge and into the opposing traffic lane. They are typically used at speeds below 25 miles per hour. Their method of action is to "shove" the show to the side, or transfer the forward vector to a sideways vector.

"Speed plows" have a shape roughly similar to a section of a triangle when viewed from the front, and a shape that is a section of a cone. Their method of action is to cause the snow to take a curved path upward on the plow face and then roll over, transferring the forward momentum of the vehicle to the snow, in a vector that is the output of the upward motion and sideways motion laterally across the plow face. This action results in throwing the snow much further off to the side than with a standard plow.

A speed plow can be operated at slow speed and produce a result similar to a standard plow. But when operated above 20 miles per hour, the rolling and throwing motion becomes predominant over the "shoving" motion. This is particularly useful on highways, to get the snow mound dispersed far off to the side of the traffic lanes.

A video search will bring up many examples of each in action. There may also be blogs and forums where plow operators hang out, and you can ask technical questions.

Replacing Gravity

drorzel — Tue, 07 Jan 2014 08:18:14 +0000

Replacing Gravity

I'm teaching introductory E&M this term, so it's kind of fun to play around with silly applications of Coulomb's Law. For example, let's imagine that gravity suddenly switched off, but we wanted to keep the Earth in its orbit. How much charge would we need to move from the Earth to the Sun for the electrostatic attraction to take the place of gravity?

The key here is to set the gravitational force, which we can reasonably approximate by Newton's Law of Universal Gravitation:

$latex F_{grav}=G\frac{M_1 m_2}{R^2} $

(where the M's are the masses, R is the distance between them, and G is a constant to get the units right) equal to the electrostatic force, which we can reasonably describe by Coulomb's Law:

$latex F_{elec}=\frac{1}{4 \pi \epsilon_0} \frac{q_1 q_2}{R^2} $

(where the q's are the charges (one positive, the other negative) and the constant to get the units right is "$latex 1/4\pi\epsilon_0 $" for historical reasons that really don't matter).

The nice thing here is that both of these depend on the distance in exactly the same way, so I don't even need to look up the radius of Earth's orbit. With a bit of algebra, we can re-arrange this to collect constants of nature on one side of the equation:

$latex \frac{q_1 q_2}{M_1 m_2} = \frac{G}{1/4\pi \epsilon_0}$

This says that you can replace gravity with electromagnetism provided these ratios are equal. There's a bit of ambiguity as to how you achieve this, though-- all that matters is the product of the charges and the product of the masses, so the individual values can vary wildly. You could hold the Earth in orbit with a single extra electron, provided you put shitloads-- metric shitloads-- of extra protons on the Sun.

Of course, that's not very practical. If you were going to do this for real, you would move some number of electrons from the Sun to the Earth, leaving behind a positive charge of the same magnitude as the negative charge the Earth acquired. In which case, you would have the same thing for both q's, and then you can easily solve for q:

$latex q = \sqrt{\frac{G}{1/ 4 \pi \epsilon_0}} \sqrt{M_1 m_2} $

So the charge you would need depends on the geometric mean of the two masses ($latex 3.5 \times 10^{27}$ kg), which is kind of cute. If you look in the back of your favorite physics textbook (you do have a favorite physics textbook, right?), you can find numbers for all these things, and get a value of:

$latex q = 3 \times 10^{17} $ C

That's a really big number-- for reference, if you shuffle your feet on the carpet and shock your younger sibling, the total amount of charge you've picked up to make that spark might be in the 10^-6C range.

Of course, since this is all a silly exercise, we can ask how many electrons that would be. The answer, again from plugging in values from the back of your favorite book, is:

$latex N = 2 \times 10^{36} $

That's enough that you might reasonably wonder whether you would be skewing the mass by enough to throw off the acceleration needed to keep the orbit going. Not to worry, though, because electrons are really light. The total mass involved is:

$latex m_{elec} = 2 \times 10^6 $ kg

So by shifting just about 2000 metric tons from the Sun to the Earth, you could replace gravity. Provided that whole mass was in electrons, and you had some magic way to keep all that charge in one place. And, for that matter, to keep the Sun burning, because if you switched gravity off, all that incandescent gas would just fly away in short order...

Another, arguably more physicist-y way to go about this would be to note that you could get the same effect by taking a star and a planet with a constant charge-to-mass ratio of around $latex 8.6 \times 10^{-11} $ C/kg. In which case you would only need about $latex 5 \times 10^{14} $ C worth of charge on the Earth, but $latex 2 \times 10^{20} $ C on the Sun.

And, just for giggles, what would you need to keep the Earth in orbit with a single extra electron? Well, you need the product of the charges to be about $latex 9 \times 10^{34} $C², in which case that single extra electron would need to be balanced by a charge of $latex 6 \times 10^{53} $ C, or about $latex 4 \times 10^{72} $ electrons. That's a mass of $latex 3 \times 10^{42} $ kg, or around a trillion times the mass of the Sun.

So, clearly, that's just completely crazy. As opposed to the other solutions, which are totally reasonable...

For homework, using the equal-charge figure above, calculate the strength of the magnetic field that would be produced due to the extra charge on the Earth acting like a current loop. Send your answers to Rhett for grading, and make sure you show all your work.

drorzel Tue, 01/07/2014 - 03:18

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"metric shitloads" merde-loads, "8^>) Gravitation does not spark (yeah well - black holes) , thus being more stable though less exciting. Sunspot AR1944 is loaded and positioned to EM blast the Earth in historic proportions. Ending electricity and communication ends Global Warming. It renormalizes armed conflict to depopulating economically disenfranchised young males. Go Maxwell!

It's everyone's favorite crazy Uncle! You deserve your own show, Uncle Al.

“metric shitloads”

kilopoops.

Right now I'm wondering about the energy loos per year due to accelerated charges (synchroton radiation). It shouldn't be too big. Well let's calculate it: del E = 2,2 * 10^22 J.

Ok maybe its not that accurate but this is about the energy you need to accelerate to earth by 0.10 m/s^2.

Another in that line is the question of what kind of magnetic field would be required to (per Velikovsky) stop the Earth's rotation, assuming the maximum surface charge consistent with the breakdown field of air.

I worked that on back in the 60s as a reply to an article on Velikovsky's attempt to rationalize Joshua.

Eli5

What would happen in your calculations if we increased the earths rotation?

If we assume that the charge is equally distributed over the whole mass of the earth (including it's inhabitants) you could calculate the acceleration you would feel due to the electrorepulsive force the earth is exerting on your charged body.

And now the fun starts, if my very quick back of the envelope calculation is correct, all the E&M terms would cancel and this would be:

G M_sun / R_earth^2

in other words equal to the gravitational acceleration you would feel if you compressed the sun to the size of the earth and were standing on it's surface.

I suspect this is strong enough to overcome atomic bonds, possibly even nuclear ones. If we charged the earth that much it would quickly transform into a rapidly expanding cloud of elementary particles.

To emphasize the relative weakness of the gravity force, Richard Feynman calculated that if two people were at arm's length, and each had one percent more electrons than protons, the electric repulsion between the two would be large enough to lift the "weight" of the entire Earth. That is, it would exceed the mass of the Earth times g.

The Elusive Niskayuna Sloth

drorzel — Sat, 26 Oct 2013 17:30:29 +0000

The Elusive Niskayuna Sloth

[Scene: In the car on the way from soccer to lunch at Five Guys. SteelyKid is in her car seat, studying the Halloween-themed temporary tattoos all over her arms.]

SteelyKid: Do bats fly right-side-up, or upside-down?

Daddy: From the bat's point of view, it's right side up more or less by definition. They do sleep upside down, though.

SK: Yeah, they're the only animals that spend their time upside down. Except sometimes monkeys. Monkeys can hang upside down from their tails, and sleep that way.

D: Well, they can certainly hang upside down sometimes. Sloths spend a lot of time hanging upside down, too.

SK: Oh, yeah, sloths. I knew about sloths, because I've seen them.

D: You have? Where?

SK: At my school. There's a really huge tree by my school, not by the playground, but over where you play baseball and games like that. There's a sloth there who lives in that tree. I've seen it there, hanging upside down.

D: Really? I didn't know we had sloths living around here.

SK: Well, it didn't used to be there. It used to live down here, in a different tree. [points out window] That tree, right over there.

D: I did not know that.

SK: Yeah. It lived there, but that's a really nice tree, so lots of other animals came to live in that tree, and then it got too crowded. There wasn't room for the sloth, so it went to live in the huge tree by my school.

D: I guess that makes sense.

SK: I saw it walking there. It was walking really slow, so slow I didn't think it was moving at all, but then I turned my back and counted to twenty, and when I turned around again, it was in the tree.

D: It must have moved pretty quickly for a while there, then, when your back was turned.

SK: No. I counted really slowly.

D: Ah. Okay, then.

SK: It was moving really slowly, and then I turned around and counted really slowly, and when I turned back around, it was up in the tree, hanging there. I saw it. And now I see it every day, in the tree, hanging upside down.

D: That's fascinating. And good thinking, by the way, to turn around and look again later. That's a good way to know if something's moving really slowly. That's thinking like a good scientist.

SK: Yeah, I knew that was a good way to see if it was moving. I don't always know what to do for science, though.

D: Well, the important thing is not just knowing stuff, but knowing how to figure stuff out. And you knew how to figure that out, which is just what a scientist should do. So, good job.

SK: Yeah, I can figure stuff out. If you need to know stuff, you can go ask the other scientists. And if they don't know, you can ask me, and I can figure it out.

D: Especially if it involves sloths in Niskayuna.

SK: Yeah. I've seen it. It hangs upside down in the tree.

[Fade out as the car turns into the Five Guys lot.]

drorzel Sat, 10/26/2013 - 13:30

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