Schroeder’s Magic Kittycat

“Bedtime, Teena.”

“Aw, Mommie, I had another question for Uncle Sy.  And I’m not sleepy yet anyhow.”

“Well, if we’re just sitting here relaxing, I suppose.  Sy, make your answer as boring as possible.”

“You know me better than that, Sis, but I’ll try.  What’s your question, Teena?”

“You said something once about quantum and Schroeder’s famous kittycat.  Why is it famous?  If it’s quantum it must be a very, very small cat.  Is it magic?”

“???… Oh, Schrödinger’s Cat.  It’s a pretend cat, not a real one, but it’s famous because it’s both asleep and awake.”

“I see what you did there, Sy.”

“Yeah, Sis, but it’s for a good cause, right?”

“But Uncle Sy, how can you tell?  Sometimes Tommie our kittycat looks sound asleep but he’s not really because he can hear when Mommie opens the cat-food can.”

“Schrödinger’s Cat is special.  Whenever he’s awake his eyes are wide open and whenever he’s asleep his eyes are shut.  And he’s in a box.”

“Tommie loves to sit in boxes.”

“Schrödinger’s Cat’s box is sealed tight.  You can’t see into it.”

“So how do you know whether he’s asleep?”

“That was Mr Schrödinger’s point.  We can’t know, so we have to suppose it’s both.  Many people have made jokes about that.  Mr. Schrödinger said the usual interpretation of quantum mechanics is ridiculous and his cat story was his way of proving that.  The cat doesn’t even have to be quantum-small and the story still works.”

“How could it be halfway?  Either his eyes are open or they’re … wait, sometimes Tommie squints, is that it?”

“Nice try, but no.  Do you remember when we were looking at the bird murmuration and I asked you to point to its middle?”

“Oh, yes, and it was making a beautiful spiral.  Mommie, you should have seen it!”

“Were there any birds right at its middle?”

“Um, no-o.  All around the middle but not right there.”

“Birds to the left, birds to the right, but no birds in the middle.  But if I’d I asked you to point to the place where the birds were, you’d’ve pointed to the middle.”

“Uh-huh.”

“You see how that’s like Mr Schrödinger’s cat’s situation?  It’s really asleep or maybe it’s really awake, but if we’re asked for just one answer we’d have to say ‘halfway between.’  Which is silly just like Mr Schrödinger said — by the usual quantum calculation we’d have to consider his cat to be half awake.  That was part of the long argument between Mr Einstein and the other scientist.”

“Wait, Sy, I didn’t hear that part of you two’s conversation on the porch.  What argument was that?”

“This was Einstein’s big debate with Niels Bohr.  Bohr maintained that all we could ever know about the quantum world are the probabilities the calculations yielded.  Einstein held that the probabilities had to result from processes taking place in some underlying reality.  Cat reality here, which we can resolve by opening the box, but the same issue applies across the board at the quantum level.  The problem’s more general than it appears, because much the same issue appears any time you can have a mixture of two or more states.  Are you asleep yet, Sweetie?”

“Nnn, kp tkng.”

“OK.  Entanglement, for instance.  Pretty much the same logic that Schrödinger disparaged can also apply to quantum particles on different paths through space.  Fire off any process that emits a pair of particles, photons for instance.  The wave function that describes both of them together persists through time so if you measure a property for one of them, say polarization direction, you know what that property is for the other one without traveling to measure it.  So far, so good.  What drove Einstein to deplore the whole theory is that the first particle instantaneously notifies the other one that it’s been measured.  That goes directly counter to Einstein’s Theory of Relativity which says that communication can’t go any faster than the speed of light.  Aaand I think she’s asleep.”

“Nice job, Sy, I’ll put her to bed.  We may discuss entanglement sometime.  G’night, Sy.”

“G’night, Sis.  Let me know the next time you do that meatloaf recipe.”

Cat emerging from murmuration~~ Rich Olcott

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What Are Quantum Birds Made Of?

“Do quantum thingies follow the same rules that birds do, Uncle Sy?”

“Mostly not, Teena.  Some quantum rules are simple, others are complicated and many are weird.”

“Tell me a simple one and a weird one.”

“Hm… the Principle of Correspondence is simple.  It says if you’ve got a lot of quantum things acting together, the whole mishmash acts by the same rules that a regular-sized thing that size would follow.  If all those birds flew in every direction there’s no flock to talk about, but if they fly by flock rules we can talk about how wind affects the flock’s motion.”

“It’s a murmuration, Uncle Sy.”

“Correction noted, Sweetie.”

“Now tell me a weird one.”

“There’s the rule that a quantum thing acts like it’s in a specific place when you look at it but it’s spread out when you’re not looking.”

“Kittie does that!  She’s never where you look for her.”

“Mm, that’s kind of in the other direction.  We see quantum particles in specific somewheres, not specific nowheres.  The rule is called wave-particle duality and people have been trying to figure out how it works for a hundred years.  Let’s try this.  Put your thumb and forefinger up to your eye and look between them at the blue sky.  Hold your fingers very close together but don’t let them touch.  What do you see?”

“Ooo, there’s stripes in between!  It looks like my finger’s going right into my thumb, but I can feel they’re not touching.  Hey, it works with my other fingers, too, but it hurts if I try it with my pinkie.”

“Then don’t do it with your pinkie, silly.  The stripes are called ‘interference’ and only waves do that.  You’ve watched how water waves go up and down, right?”

“Sure!”

“When the high part of one wave meets the low part of another wave, what happens?”

“I guess high and low make middle.”

“Good guess, that’s exactly right.  That little teeny space between your fingers lets through only certain waves.  You see light where the highs and lows are, dark where the waves middle out.”

“So light’s made out of waves, huh?”

“Well, except that scientists have done lots of experiments where light behaves like it’s made out of little particles called photons.  The funny thing is, light always acts like a wave when it’s traveling from one place to another, but at both ends of the trip it always acts like photons.  That’s the big mystery — how does it do that?”

“You know how it works, don’tcha, Uncle Sy?”

“Only kinda sorta, Teena.  I think it has to do with the idea of big things made out of little things made out of littler things.  Einstein — wait, you know who Einstein was, right?”

“He was the famous scientist with the big hair.”

“That’s right.  He and another scientist had a big debate over 80 years ago.  The other scientist said that when quantum things make patterns, like those stripes you’re looking at, the patterns are all we can know about them.  Einstein said that there has to be something deeper down that drives the patterns.”

“Who won the debate?”

“At the time most people thought that the other man had, but philosophies change.  Since that time lots of people have followed Einstein’s thinking.  Some of the theories are pretty silly, I think, but I’m betting on birds made out of birds.”

“That’s silly, too, Uncle Sy.”

“Maybe, maybe not, we’ll see some day.  It starts with what you might call ‘the smallness quantum,’ though it’s also called ‘the Planck length‘ after Mr Planck who helped invent quantum mechanics.  The Planck length is awesomely small.  It’s as much smaller than us as we are smaller than the whole universe.”

“But there’s lots of things bigger than we are.”

“Exactly.  We’re smaller than whales, they’re smaller than planets, planets are smaller than suns, and galaxies, and on up.  But we don’t know near as many size scales in the other direction – us and bacteria and atoms and protons and that’s about it.  I think there’s plenty of room down there for structures and chaos we’ve not thought of yet.”

“Like birds in murmurations.”

“Mm-hmm.”Bird made out of birds 1

~~ Rich Olcott

Einstein’s Revenge

Vinnie’s always been a sucker for weird-mutant sci-fi films so what Jennie says gets him going.  “So you got these teeny-tiny neutrinos and they mutate?  What do they do, get huge and eat things?”

“Nothing that interesting, Vinnie — or uninteresting, depending on what you’re keen on.  No, what happens is that each flavor neutrino periodically switches to another flavor.”

“Like an electron becomes a muon or whatever?”

“Hardly.  The electron and muon and tau particles themselves don’t swap.  Their properties differ too much —  the muon’s 200 times heaver than the electron and the tau’s sixteen times more massive than that.  It’s their associated neutrinos that mutate, or rather, oscillate.  What’s really weird, though, is how they do that.”

“How’s that?”

“As I said, they cycle through the three flavors.  And they cycle through three different masses.”

“OK, that’s odd but how is it weird?”

“Their flavor doesn’t change at the same time and place as their mass does.”Neutrino braid with sines

“Wait, what?”

“Each kind of neutrino, flavor-wise, is distinct — it reacts with a unique set of particles and yields different reaction products to what the other kinds do.  But experiments show that the mass of each kind of neutrino can vary from moment to moment.  At some point, the mass changes enough that suddenly the neutrino’s flavor oscillates.”

“That makes me think each mass could be a mix of three different flavors, too.”

“Capital, Vinnie!  That’s what the math shows.  It’s two different ways of looking at the same coin.”

“The masses oscillate, too?”

“Oh, indeed.  But no-one knows exactly what the mass values are nor even how the mass variation controls the flavors.  Or the other way to.  We know two of the masses are closer together than to the third but that’s about it.  On the experimental side there’s loads of physicists and research money devoted to different ways of measuring how neutrino oscillation rates depend on neutrino energy content.”

“And on the theory side?”

“Tons of theories, of course.  Whenever we don’t know much about something there’s always room for more theories.  The whole object of experiments like IceCube is to constrain the theories.  I’ve even got one I may present at Al’s Crazy Theory Night some time.”

“Oh, yeah?  Let’s hear it.”

“It’s early days, Al, so no flogging it about, mm?  Do you know about beat frequencies?”

“Yeah, the piano tuner ‘splained it to me.  You got two strings that make almost the same pitch, you get this wah-wah-wah effect called a beat.  You get rid of it when the strings match up exact.”  He grabs a few glasses from the counter and taps them with a spoon until he finds a pair that’s close.  “Like this.”

“Mm-hmm, and when the wah-wahs are close enough together they merge to become a note on their own.  You can just imagine how much more complicated it gets when there are three tones close together.”

I see where she’s going and bring up a display on Old Reliable —an overlay of three sine waves.   “Here you go, Jennie.  The red line is the average of the three regular waves.”Three sines on Old Reliable“Thanks, Sy.  Look, we’ve got three intervals where everything syncs up.  See the new satellite peaks half-way in between?  There’s more hidden pattern where things look chaotic in the rest of the space.”

“Yeah, so?”

“So, Vinnie, my crazy theory is that like a photon’s energy depends on its wave frequency in the electromagnetic field, a neutrino is a combination of three weak-field waves of slightly different frequency, one for each mass.  When they sync up one way you’ve got an electron neutrino, when they sync up a different way you’ve got a muon neutrino, and a third way for a tau neutrino.”

I’ve got to chuckle.  “Nothing against your theory, Jennie, though you’ve got some work ahead of you to flesh it out and test it.  I just can’t help thinking of Einstein and his debates with Bohr.  Bohr maintained that all we can know about the quantum realm are the averages we calculate.  Einstein held that there must be understandable mechanisms underlying the statistics.  Field-based theories like yours are just what Einstein ordered.”

“I could do worse.”Neutrino swirl around Einstein

~~ Rich Olcott

Water, Water Everywhere — How Come?

Lunch time, so I elbow my way past Feder and head for the elevator.  He keeps peppering me with questions.

“Was Einstein ever wrong?”

“Sure. His equations pointed the way to black holes but he thought the Universe couldn’t pack that much mass into that small a space.  It could.  There are other cases.”

We’re on the elevator and I punch 2.  “Where you going?  I ain’t done yet.”

“Down to Eddie’s Pizza.  You’re buying.”

“Awright, long as I get my answers.  Next one — if the force pulling an electron toward a nucleus goes as 1/r², when it gets to where r=0 won’t it get stuck there by the infinite force?”

“No, because at very short distances you can’t use that simple force law.  The electron’s quantum wave properties dominate and the charge is a spread-out blur.”

The elevator stops at 7.  Cathleen and a couple of her Astronomy students get on, but Feder just peppers on.  “So I read that everywhere we look in the Solar System there’s water.  How come?”

I look over at Cathleen.  “This is Mr Richard Feder of Fort Lee, NJ.  He’s got questions.  Care to take this one?  He’s buying the pizza.”

“Well, in that case.  It all starts with alpha particles, Mr Feder.”

The elevator door opens on 2, we march into Eddie’s, order and find a table.  “What’s an alpha particle and what’s that got to do with water?”

Alpha particle

Two protons and two neutrons, assembled as an alpha particle

“An alpha particle’s a fragment of nuclear material that contains two protons and two neutrons.  99.999% of all helium atoms have an alpha particle for a nucleus, but alphas are so stable relative to other possible combinations that when heavy atoms get indigestion they usually burp alpha particles.”

“And the water part?”

“That goes back to where our atoms come from — all our atoms, but in particular our hydrogen and oxygen.  Hydrogen’s the simplest atom, just a proton in its nucleus.  That was virtually the only kind of nucleus right after the Big Bang, and it’s still the most common kind.  The first generation of stars got their energy by fusing hydrogen nuclei to make helium.  Even now, that’s true for stars about the size of the Sun or smaller.  More massive stars support hotter processes that can make heavier elements.  Umm, Maria, do you have your class notes from last Tuesday?”

“Yes, Professor.”

“Please show Mr Feder that chart of the most abundant elements in the Universe.  Do you see any patterns in the second and fourth columns, Mr Feder?”

Element Atomic number Mass % *103 Atomic weight Atom % *103
Hydrogen 1 73,900 1 92,351
Helium 2 24,000 4 7,500
Oxygen 8 1,040 16 81
Carbon 6 460 12 48
Neon 10 134 20 8
Iron 26 109 56 2
Nitrogen 7 96 14 <1
Silicon 14 65 32 <1

“Hmm…  I’m gonna skip hydrogen, OK?  All the rest except nitrogen have an even atomic number, and all of ’em except nitrogen the atomic weight is a multiple of four.”

“Bravo, Mr Feder.  You’ve distinguished between two of the primary reaction paths that larger stars use to generate energy.  The alpha ladder starts with carbon-12 and adds one alpha particle after another to go from oxygen-16 on up to iron-56.  The CNO cycle starts with carbon-12 and builds alphas from hydrogens but a slow step in the cycle creates nitrogen-14.”

“Where’s the carbon-12 come from?”

“That’s the third process, triple alpha.  If three alphas with enough kinetic energy meet up within a ridiculously short time interval, you get a carbon-12.  That mostly happens only while a star’s going nova, simultaneously collapsing its interior and spraying most of its hydrogen, helium, carbon and whatever out into space where it can be picked up by neighboring stars.”

“Where’s the water?”

“Part of the whatever is oxygen-16 atoms.  What would a lonely oxygen atom do, floating around out there?  Look at Maria’s table.  Odds are the first couple of atoms it runs across will be hydrogens to link up with.  Presto!  H2O, water in astronomical quantities.  The carbon atoms can make methane, CH4; the nitrogens can make ammonia, NH3; and then photons from Momma star or somewhere can help drive chemical reactions  between those molecules.”

“You’re saying that the water astronomers find on the planets and moons and comets comes from alpha particles inside stars?”

“We’re star dust, Mr Feder.”

~~ Rich Olcott

Abstract Horses

It was a young man’s knock, eager and a bit less hesitant than his first visit.

“C’mon in, Jeremy, the door’s open.”

“Hi, Mr Moire, it’s me, Jerem…  How did ..?  Never mind.  Ready for my black hole questions?”

“I’ll do what I can, Jeremy, but mind you, even the cosmologists are still having a hard time understanding them.  What’s your first question?”

“I read where nothing can escape a black hole, not even light, but Hawking radiation does come out because of virtual particles and what’s that about?”

“That’s a very lumpy question.  Let’s unwrap it one layer at a time.  What’s a particle?”

“A little teeny bit of something that floats in the air and you don’t want to breathe it because it can give you cancer or something.”

“That, too, but we’re talking physics here.  The physics notion of a particle came from Newton.  He invented it on the way to his Law of Gravity and calculating the Moon’s orbit around the Earth.  He realized that he didn’t need to know what the Moon is made of or what color it is.  Same thing for the Earth — he didn’t need to account for the Earth’s temperature or the length of its day.  He didn’t even need to worry about whether either body was spherical.  His results showed he could make valid predictions by pretending that the Earth and the Moon were simply massive points floating in space.”

Accio abstractify!  So that’s what a physics particle is?”

“Yup, just something that has mass and location and maybe a velocity.  That’s all you need to know to do motion calculations, unless the distance between the objects is comparable to their sizes, or they’ve got an electrical charge, or they move near lightspeed, or they’re so small that quantum effects come into play.  All other properties are irrelevant.”

“So that’s why he said that the Moon was attracted to Earth like the apple that fell on his head was — in his mind they were both just particles.”

“You got it, except that apple probably didn’t exist.”

“Whatever.  But what about virtual particles?  Do they have anything to do with VR goggles and like that?”

“Very little.  The Laws of Physics are optional inside a computer-controlled ‘reality.’  Virtual people can fly, flow of virtual time is arbitrary, virtual electrical forces can be made weaker or stronger than virtual gravity, whatever the programmers decide will further the narrative.  But virtual particles are much stranger than that.”

“Aw, they can’t be stranger than Minecraft.  Have you seen those zombie and skeleton horses?”Horses

“Yeah, actually, I have.  My niece plays Minecraft.  But at least those horses hang around.  Virtual particles are now you might see them, now you probably don’t.  They’re part of why quantum mechanics gave Einstein the willies.”

“Quantum mechanics comes into it?  Cool!  But what was Einstein’s problem?  Didn’t he invent quantum theory in the first place?”

“Oh, he was definitely one of the early leaders, along with Bohr, Heisenberg, Schrödinger and that lot.  But he was uncomfortable with how the community interpreted Schrödinger’s wave equation.  His row with Bohr was particularly intense, and there’s reason to believe that Bohr never properly understood the point that Einstein was trying to make.”

“Sounds like me and my Dad.  So what was Einstein’s point?”

“Basically, it’s that the quantum equations are about particles in Newton’s sense.  They lead to extremely accurate predictions of experimental results, but there’s a lot of abstraction on the way to those concrete results.  In the same way that Newton reduced Earth and Moon to mathematical objects, physicists reduced electrons and atomic nuclei to mathematical objects.”

“So they leave out stuff like what the Earth and Moon are made of.  Kinda.”

“Exactly.  Bohr’s interpretation was that quantum equations are statistical, that they give averages and relative probabilities –”

“– Like Schrödinger’s cat being alive AND dead –”

“– right, and Einstein’s question was, ‘Averages of what?‘  He felt that quantum theory’s statistical waves summarize underlying goings-on like ocean waves summarize what water molecules do.  Maybe quantum theory’s underlying layer is more particles.”

“Are those the virtual particles?”

“We’re almost there, but I’ve got an appointment.  Bye.”

“Sure.  Uhh… bye.”

~~ Rich Olcott

Does a photon experience time?

My brother Ken asked me, “Is it true that a photon doesn’t experience time?”  Good question.  As I was thinking about it I wondered if the answer could have implications for Einstein’s bubble.

When Einstein was a grad student in Göttingen, he skipped out on most of the classes given by his math professor Hermann Minkowski.  Then in 1905 Einstein’s Special Relativity paper scooped some work that Minkowski was doing.  In response, Minkowski wrote his own paper that supported and expanded on Einstein’s.  In fact, Minkowski’s contribution changed Einstein’s whole approach to the subject, from algebraic to geometrical.

But not just any geometry, four-dimensional geometry — 3D space AND time.  But not just any space-AND-time geometry — space-MINUS-time geometry.  Wait, what?Pythagoras1

Early geometer Pythagoras showed us how to calculate the hypotenuse of a right triangle from the lengths of the other two sides. His a2+b2 = c2 formula works for the diagonal of the enclosing rectangle, too.

Extending the idea, the body diagonal of an x×y×z cube is √(x2+y2+z2) and the hyperdiagonal  of a an ct×x×y×z tesseract is √(c2t2+x2+y2+z2) where t is time.  Why the “c“?  All terms in a sum have to be in the same units.  x, y, and z are lengths so we need to turn t into a length.  With c as the speed of light, ct is the distance (length) that light travels in time t.

But Minkowski and the other physicists weren’t happy with Pythagorean hyperdiagonals.  Here’s the problem they wanted to solve.  Suppose you’re watching your spacecraft’s first flight.  You built it, you know its tip-to-tail length, but your telescope says it’s shorter than that.  George FitzGerald and Hendrik Lorentz explained that in 1892 with their length contraction analysis.

What if there are two observers, Fred and Ethel, each of whom is also moving?  They’d better be able to come up with the same at-rest (intrinsic) size for the object.

Minkowski’s solution was to treat the ct term differently from the others.  Think of each 4D address (ct,x,y,z) as a distinct event.  Whether or not something happens then/there, this event’s distinct from all other spatial locations at moment t, and all other moments at location (x,y,z).

To simplify things, let’s compare events to the origin (0,0,0,0).  Pythagoras would say that the “distance” between the origin event and an event I’ll call Lucy at (ct,x,y,z) is √(c2t2+x2+y2+z2).

Minkowski proposed a different kind of “distance,” which he called the interval.  It’s the difference between the time term and the space terms: √[c2t2 + (-1)*(x2+y2+z2)].

If Lucy’s time is t=0 [her event address (0,x,y,z)], then the origin-to-Lucy interval is  √[02+(-1)*(x2+y2+z2)]=i(x2+y2+z2).  Except for the i=√(-1) factor, that matches the familiar origin-to-Lucy spatial distance.

Now for the moment let’s convert the sum from lengths to times by dividing by c2.  The expression becomes √[t2-(x/c)2-(y/c)2-(z/c)2].  If Lucy is at (ct,0,0,0) then the origin-to-Lucy interval is simply √(t2)=t, exactly the time difference we’d expect.

Finally, suppose that Lucy departed the origin at time zero and traveled along x at the speed of light.   At any time t, her address is (ct,ct,0,0) and the interval for her trip is √[(ct)2-(ct)2-02-02] = √0 = 0.  Both Fred’s and Ethel’s clocks show time passing as Lucy speeds along, but the interval is always zero no matter where they stand and when they make their measurements.

Feynman diagramOne more step and we can answer Ken’s question.  A moving object’s proper time is defined to be the time measured by a clock affixed to that object.  The proper time interval between two events encountered by an object is exactly Minkowski’s spacetime interval.  Lucy’s clock never moves from zero.

So yeah, Ken, a photon moving at the speed of light experiences no change in proper time although externally we see it traveling.

Now on to Einstein’s bubble, a lightwave’s spherical shell that vanishes instantly when its photon is absorbed by an electron somewhere.  We see that the photon experiences zero proper time while traversing the yellow line in this Feynman diagram.  But viewed from any other frame of reference the journey takes longer.  Einstein’s objection to instantaneous wave collapse still stands.

~~ Rich Olcott

The question Newton couldn’t answer

250 years ago, when people were getting used to the idea that the planets circle the Sun and not the other way around, they wondered how that worked.  Isaac Newton said, “I can explain it with my Laws of Motion and my Law of Gravity.”

The first Law of Motion is that an object will move in a straight line unless acted upon by a force.  If you’re holding a ball by a string and swing the ball in a circle, the reason the ball doesn’t fly away is that the string is exerting a force on the ball.  Using Newton’s Laws, if you know the mass of the ball and the length of the string, you can calculate how fast the ball moves along that circle.

Newton said that the Solar System works the same way.  Between the Sun and each planet there’s an attractive force which he called gravity.  If you can determine three points in a planet’s orbit, you can use the Laws of Motion and the Law of Gravity to calculate the planet’s speed at any time, how close it gets to the Sun, even how much the planet weighs.

Astronomers said, “This is wonderful!  We can calculate the whole Solar System this way, but… we don’t see any strings.  How does gravity work?”

Newton was an honest man.  His response was, “I don’t know how gravity works.  But I can calculate it and that should be good enough.”

And that was good enough for 250 years until Albert Einstein produced his Theories of Relativity.  This graphic shows one model of Einstein’s model of “the fabric of space.”  According to the theory, light (the yellow threads) travels at 186,000 miles per second everywhere in the Universe.

Fabric of Space 4a

As we’ve seen, the theory also says that space is curved and compressed near a massive object.  Accordingly, the model’s threads are drawn together near the dark circle, which could represent a planet or a star or a black hole.  If you were standing next to a black hole (but not too close). you’d feel fine because all your atoms and the air you breathe would shrink to the same scale.  You’d just notice through your telescope that planetary orbits and other things in the Universe appear larger than you expect.FoS wave

This video shows how a massive object’s space compression affects a passing light wave.  The brown dot and the blue dot both travel at 186,000 miles per second, but “miles are shorter near a black hole.”  The wave’s forward motion is deflected around the object because the blue dot’s miles are longer than the miles traveled by the brown dot.

When Einstein presented his General Theory of Relativity in 1916, his calculations led him to predict that this effect would cause a star’s apparent position to be altered by the Sun’s gravitational field. Fabric of Space 4b

An observer at the bottom of this diagram can pinpoint the position of star #1 by following its light ray back to the star’s location.  Star #2, however, is so situated that its light ray is bent by our massive object.  To the observer, star #2’s apparent position is shifted away from its true position.

In 1919, English physicist-astronomer Arthur Eddington led an expedition to the South Atlantic to test Einstein’s prediction.  Why the South Atlantic?  To observe the total eclipse of the sun that would occur there.  With the Sun’s light blocked by the Moon, Eddington would be able to photograph the constellation Taurus behind the Sun.

Sure enough, in Eddington’s photographs the stars closest to the Sun were shifted in their apparent position relative to those further way.  Furthermore, the sizes of the shifts were almost embarrassingly close to Einstein’s predicted values.

Eddington presented his photographs to a scientific conference in Cambridge and thus produced the first public confirmation of Einstein’s theory of gravity.

Wait, how does an object bending a light ray connect with that object’s pull on another mass?  Another piece of Einstein’s theory says that if a light ray and a freely falling mass both start from the same point in spacetime, both will follow the same path through space.  American physicist John Archibald Wheeler said, “Mass bends space, and bent space tells mass how to move.”

 

~~ Rich Olcott