Happy 95th Anniversary, Relativity

StartsWithABang (3485481) writes "It's hard to believe, but there are people alive today who remember a world where Newtonian gravity was the accepted theory of gravitation governing our Universe. 95 years ago today, the 1919 solar eclipse provided the data that would provide the test of the three key options for how light would respond to the presence of a gravitational field: would it not bend at all? Would it bend according to Newton's predictions if you took the "mass" of a photon to be E/c^2? Or would it bend according to the predictions of Einstein's wacky new idea? Celebrate the 95th anniversary of relativity's confirmation by reliving the story."

Comments

95 years but

[rossdee]

its less than that time if it was travelling at significant speed

Re:95 years but

[Anonymous Coward]

Eh, it's all relative.

Re:95 years but

[buchner.johannes]

Eh, it's all relative.

Except for the speed of light. That is absolute.

Re:95 years but

[Ol Olsoc]

Eh, it's all relative.

Except for the speed of light. That is absolute.

Nope. Depends on the medium and it's velocity factor. http://en.wikipedia.org/wiki/V...

And no, creationists, that does not prove your whack-a-doodle variable speed of light conjecture.

Re:95 years but

[barlevg]

I realize you were making a joke based on a perception common in popular culture, but the truth is that the Schrodinger's Cat paradox has a simple resolution: the cat *cannot* be both alive and dead because the detector (which detects whether the decay has occurred and which triggers the release of the poison if the decay occurred) collapses the wave function of the particle. There's no such thing as a passive detector. So while a subatomic particle could indeed exist in a superposition of "decayed" vs. "not decayed," the second you go about asking the particle whether it's decayed (that is, when you set up the detector), the wave function collapses, and no superposition is possible.

Re:95 years but

[barlevg]

The photons themselves are still traveling at c. What's "slowing them down" is that they're being absorbed and re-emitted by the atoms in the medium. The speed of light is absolute.

Re:95 years but

[Eunuchswear]

Well, it depends.

If you go many-worlds then the cat is both alive and dead - but in the world were you are, yes, it's either alive or dead.

Re:95 years but

[barlevg]

Well sure, but in many-worlds, it's also alive because you never put it in the box*, and it's also a dog, and it also passed straight through the walls of the box and into the Earth's molten core.

*Not to say that conscious decisions are directly quantum events, but quantum mechanics causes thermal fluctuations, and the brain is likely chaotic enough that the right fluctuation at the right time could create a different decision. The odds of all this happening are infinitesimal, but according to many-worlds, as long as it was nonzero, it must have still happened in some universe.

Re:95 years but

[Ol Olsoc]

The photons themselves are still traveling at c. What's "slowing them down" is that they're being absorbed and re-emitted by the atoms in the medium. The speed of light is absolute.

Cherenkov radiation

Re:95 years but

[barlevg]

Exactly my point. The light in Cherenkov radiation isn't travelling faster than c, it's just going faster than the "c" for that medium.

Re:95 years but

[drinkypoo]

Well sure, but in many-worlds, it's also alive because you never put it in the box*, and it's also a dog, and it also passed straight through the walls of the box and into the Earth's molten core.

Nah, that's infinite-worlds.

Re:95 years but

[Richy_T]

It's not known what counts as an "observer". This is a major problem with the Copenhagen interpretation (not that other interpretations don't have their own issues).

Re:95 years but

[nitehawk214]

Yes but you and the cat are only in one of those worlds. There is no such thing as "the same cat in a different world". It is a different cat that branched off at some time in the past. Therefore no matter which interpretation you use, the cat is either alive or dead, full stop.

Re:95 years but

[doug141]

At what physical size within an isolated system is the detector (be it a photon, an atom, a molecule, a geiger counter, a cat, or an experimenter opening a box) no longer allowed by physical laws be in a quantum superposition?

Re:95 years but

[barlevg]

There's no fixed limit--the double-slit experiment has been run on gold particles, I know, I think I heard of it even being performed on DNA molecules. It's not about the size, it's about the act of measurement. However, I've gotten responses in the other place I posted this comment that are basically along the lines of, "there's a certain class of detectors that will entangle with the system rather than collapse it." If that's the case, then the Schrodinger's Cat problem becomes a practical one (it's impossible to truly isolate the cat from the outside world) than the fundamental one I've described.

Re:95 years but

[rogoshen1]

are you implying that cats have souls, and that there is in fact a cafterlife? (cat+afterlife, sorry.)

Re:95 years but

[doug141]

My impression of the thought experiment was that it was actually asking the listener to consider questions like "if the universe is isolated, are we in superposition right now?" and "what is the relationship between consciousness and superposition?" At any rate, it has been fascinating to watch the moderation of your "simple resolution" post bounce between extremes.

Re:95 years but

[barlevg]

See, that's the danger, and why I made my original comment in the first place: Schrodinger's cat (and Quantum Mechanics as a whole) has absolutely nothing to do with consciousness. Here's a great piece explaining in more detail.

Re:95 years but

[doug141]

Bell's inequality proved quantum states are not determined before observation.

Re:95 years but

[the_other_chewey]

Exactly my point. The light in Cherenkov radiation isn't travelling faster than c, it's just going faster than the "c" for that medium.

The particle triggering the radiation is, the Cherenkov photons themselves are not -
that's what makes those nice Mach-like Cherenkov cones.

Re:95 years but

[ByteSlicer]

There's no such thing as a passive detector.

Sure there is. There is nothing special about a detector. If you can put a whole cat (=a bunch of atoms) in a superposition of quantum states, you can also include the detector (=a bunch of atoms) in that superposition.

It only works if the inside of the box (including the detector) is isolated from the rest of the universe. Then there is a superposition of 2 states: (1) the radioisotope didn't decay, the detector detected nothing, the cat is alive; and (2) the radioisotope decayed, the detector detected the emitted particle and released the neurotoxin, the cat died.

Once you break isolation (i.e. coherence), the rest of the universe entangles (at random) with one of these states, and the other state "collapses".

The big question is: what happens with the collapsed state? Was it absorbed in the other state? Did it entangle with a parallel universe? Did it become disconnected from reality?

Re:95 years but

[mattack2]

Well, I surely can detect that you posted the same response both in this thread and the "Scientists Find Method To Reliably Teleport Data" one.

Re:95 years but

[barlevg]

This is wrong. Before one "collapses" a particle's state, it actually *does* exist in all states simultaneously. See the double-slit experiment.

Simultaneity is in the eye of the beholder.

[mpoulton]

95 years of confusing the heck out of second-semester physics students! You didn't think you signed up for a calculus-based philosophy class with numerical answers to epistemological questions...

Re:Simultaneity is in the eye of the beholder.

[barlevg]

The truth is, relativity doesn't have to be as confusing as it's usually made out to be. The most accessible explanation I've found for time dilation came from Brian Greene's The Elegant Universe :

Suppose you have a race car that can only go 100 m/s, no faster, no slower. Suppose it's racing down a very wide track that's 1km in length . Depending on the angle at which the car travels, it may cross the finish line in 10 seconds, 20, 50 or however long, just no less than 10 seconds. So similarly, we can think of our journey through the universe as happening along a "time" direction as well as three "space" directions: the faster we travel through space, necessarily the slower we travel through time, but no matter what, we're travelling at c.

The math even works out, in terms of c=sqrt(v_x^2+v_t^2) where "v_t" (your velocity through time) is c*dtau/dt.

This analogy obviously only gets you so far, and the real "wow" of relativity comes from the concepts of simultaneity (I wish more SF authors realized that FTL and time travel are the same friggin' thing), but especially for non-majors this is a great way to get one's foot in the door and begin to understand what is a pretty alien concept.

Re:Simultaneity is in the eye of the beholder.

[Jason Levine]

I never found relativity to be that hard or confusing. Now quantum mechanics on the other hand.... *shudders*

Re:Simultaneity is in the eye of the beholder.

[TopherC]

Funny, I read that book (which is excellent) but don't remember that analogy. But I think you're talking about special relativity, not general relativity. The best GR explanation I've seen is an article Lost in Hyperbolia. For me that explanation worked perfectly.

Now I remember reading in various places that the solar eclipse data on GR was not actually conclusive. Bad science. The earlier work Einstein did that explained the precession of mercury's orbit was actually the first confirmation of GR. Also, of course, confirmation is not a word that is ever used correctly in science. The precession of mercury's orbit disproved Newtonian gravity but failed to disprove GR. The bending of starlight by the Sun would have been an even more impressive failure-to-disprove GR if the data were actually conclusive.

Re:Simultaneity is in the eye of the beholder.

[barlevg]

Indeed. Parent was talking about Special (simultaneity).

Re: Mercury's precession, I'm still a believer in Vulcan.

Re:Simultaneity is in the eye of the beholder.

[TopherC]

Oh, what I do remember from Bairn Greene's The Elegant Universe was his analogy for Bell's Inequality. Looks like that has been put up on Wikipedia.

Re:Simultaneity is in the eye of the beholder.

[TopherC]

Re: Mercury's precession, I'm still a believer in Vulcan.

Yeah, even the term "disproves" is not exactly correct. Newtonian gravity has a very hard time explaining Mercury's precession and is completely untenable with today's observational evidence. General relativity explains Mercury's orbit without having to invent new invisible planets & stuff. And today General relativity is still doing spectacularly well with many careful neutron star observations as well as experiments closer to home, like Gravity Probe B's measurements of frame dragging and more.

95?

[Tablizer]

Meh, anniversaries are relative.

Re:I don't believe in relativity

[Anonymous Coward]

It's nowhere to be found in Genesis.

So now that we have had the official American view on the matter, any other nationalities care to chime in?

Re:I don't believe in relativity

[The Rizz]

Not sure what a British rock group has to do with a German/Swiss/American physicist's work, but whatever...

Does mass matter?

[tonywestonuk]

"Would it bend according to Newton's predictions if you took the "mass" of a photon to be E/c^2?" Did Newton predict that the 'bend' of something in a gravitational field, was related to its mass?? I always thought it was speed that mattered. Doesn't matter if its an atom, or a hammer., both will bend the same way.

Re:Does mass matter?

[Sockatume]

Newton's law of universal gravitation doesn't include velocity at all; it's just the product of the masses over the square of the distance between them.

Re:Does mass matter?

[Sockatume]

Ha, actually looking at the physics shows that the mass just cancels out and velocity is all that matters. Newton didn't predict this though, lacking a good velocity for light.

Re:Does mass matter?

[TapeCutter]

Newton's primary insight is the gravitational field, ie: two bodies attract each other with a force proportional to the combined masses and the distance between them. That he invented calculus to prove it and wrote it all down in his "Principia" is why he is remembered. A photon is neither a hammer , nor an atom. Photons did not have mass so they were believed to be unaffected by gravity. Einstein came along and said mass and energy are two forms of the same thing and a photon would be affected by gravity. The experiment in TFA allowed the universe to make the final call.

Trivia: Newton's Principa contains only two explicit assumptions, one of them was the assumption that "time is constant".

Re:Does mass matter?

[Anonymous Coward]

Trivia: Newton's Principa contains only two explicit assumptions, one of them was the assumption that "time is constant".

I was under the impression that Leibniz though disagreed:

https://en.wikipedia.org/wiki/Philosophy_of_space_and_time#Leibniz_and_Newton

Re:Does mass matter?

[AthanasiusKircher]

Newton's primary insight is the gravitational field, ie: two bodies attract each other with a force proportional to the combined masses and the distance between them.

It's worth noting that this insight was not at all unique to Newton. There was, in fact, a major dispute in the scientific community about who came up with this idea at the time, since Robert Hooke had already published on this notion. Other scientists had basically also postulated similar ideas in the decades before the Principia.

That he invented calculus to prove it and wrote it all down in his "Principia" is why he is remembered.

Yes -- Newton may have been the first to explicitly identify the specific inverse square relationship (rather than a general form relationship mentioned in the first quotation above), and he had the mathematical apparatus to prove how it all worked.

But it's also important to be clear that the idea of a "gravitational field" or an "unseen force acting at a distance" was a very spooky and strange notion to contemporary scientists in Newton's era. In fact, such ideas were commonly associated with occult ideas; they didn't fit in with the conception of a simple mechanistic universe. Thus, Newton's idea of some strange unseen "force" acting across vast distances would seem like invoking the power of God or angels or some mystical astrological "force" today.

Because of that, many scientists were initially very suspicious of Newton's methodology. Newton therefore wrote a clarification as an appendix to the second edition of the Principia explicitly saying he was NOT assuming the existence of unseen forces and fields. Instead, he claimed his model was valuable simply because the mathematics were an accurate model. (Some historians have argued that this was in fact the most important element of Newton's revolution in thought: he argued for the acceptance of a mathematical model as a scientific explanation, even if we can't explain the underlying causes of that model.) Of course, Newton was a pretty weird guy and believed in all sorts of things that modern science would think weird, so obviously he thought the unseen forces were real. But it's interesting that he worked so hard to distance himself from such ideas at the time -- to be in accord with science of the time, the "force" in his model was thus to be considered a mere mathematical contrivance, rather than how the universe actually worked.

Re:Does mass matter?

[fermion]

This is where not understanding science makes everything wonky. The major problems with Newtonian physics is domain and history. In the later, we observe nature and sometimes see energy moving through a medium and call that a wave. We see object that we can hold an call that mass. Our experience then tells us that some things are waves and some things are mass. It is like an ancient person seeing a piece of wood catch on fire and saying that the fire was in the wood. Current experiments do support such a view, and in as much as Newton assumed that these were separate domains, the theory is wrong even if try to retcon it.

The second issue is domain. At the time of newton nothing moved very fast, so no one apparently thought to 'for slow moving objects' to the theory. Therefore there was no limit to how fast things could go. Einstien added the limit to how fast things could go, making Newtonian mechanics a good approximation for slow moving objects, but still incorrect overall. As Newton had no concept of the speed of light as a limiting factor, and separated the concept of waves and matter, there again is no reasonable basis to retcon classical mechanics.

It is interesting that people fixate on relativity. Like any other modern theory it value is in what new phenomena is can predict that can then be verified. I am somewhat part of the class of physics people that rolls my eyes when people start taking about how great Einstein is and feel justified because after all, when they gave him the noble prize for the photoelectric effect, which was a clever experiment but proved nothing, they also included a grave insult by calling what he did epistemology, and after all it only indicated that the Photon might not be just a particle or a wave. I believe it was the Michaelson-Morley experiment did a much better job of leading us to wave-particle duality, along with the work of Max Plank.

In any case, Newton also left us with another problem. The mathematical distinction between gravitational and inertial mass. These two were never well connected even though they appeared to be the same thing. Einstein kind of circumvented the whole thing with his geometry interpretation. Again, Newton is correct in the interpretation.

I think where the teaching of Relativity fails is that it focuses too much on trains, rulers, and clock because those were things that existed in 1900 and we like to think that history will make things more concrete and acceptable to the student. But arguably Relativity is about whether it makes a difference if you are moving past the magnet or if the magnet is moving past you. Is a deeper concept, but maybe we should try to teach the deep concept instead of just focusing on the mathematical manipulations.

Re:Does mass matter?

[drinkypoo]

Newton therefore wrote a clarification as an appendix to the second edition of the Principia explicitly saying he was NOT assuming the existence of unseen forces and fields. Instead, he claimed his model was valuable simply because the mathematics were an accurate model.

But that was some pretty weaselly bullshit, because that's precisely what he was describing mathematically. And per your link, the text which you claim distances him from unseen forces and fields in fact assumes the existence of unseen forces and fields, simply attributing the forces to God.

Re:Does mass matter?

[mattack2]

Of course, Newton was a pretty weird guy and believed in all sorts of things that modern science would think weird

Covered in a 2005 episode of Nova. See it here
http://www.pbs.org/wgbh/nova/p...

Re: I don't believe in relativity

[Anonymous Coward]

It is found in several places in Qur'an if that's the comment that you're after

Re:I don't believe in relativity

[Anonymous Coward]

It's nowhere to be found in Genesis.

Sure it is! How do you think Methuselah lived for 969 years? Time dilation, dude.

Why not 100?

[Sockatume]

Of course, we're celebrating this now because its age will only asymptotically approach 100 years.

Re:Why not 100?

[maroberts]

Amusing, but on seeing this news article I can't help but wonder if Slashdot celebrated every 5 year anniversary with such enthusiasm. 95 isn't really a special marker, and this story is a bit of a non-event.

Re:peh

[Urkki]

Wouldn't it be more fun to relive the story of the first time he got laid?

That's not something to celebrate publicly. Gentlemen and Ladies don't kiss and tell.

Re:I don't believe in relativity

[TapeCutter]

Einstein was a (mono-cranium) Tasmanian, his theory of roll and rock has been well documented. The drummer in Genesis had been accused of robbing a train and fled the UK, he went to the most remote place on the planet he could think of (Oz) and witnessed Einstein giving a lecture about the theory of "roll and rock. You will notice 'Bert had, by this time, renamed his theory to the more familiar "rock and roll" which is what Ronald Biggs heard and took with him to Genesis - (BTW, that black haired beauty with big brown eyes in the lecture video is a young Marie Curie).

99 Years

[physburn]

I make it 99 years since general relavity was written, and 110 years since special relavity was written, what is so special about the first confirming solar eclipse that marks it the beginning of relavity, the solar eclipse meanly showed that light could be bent by gravity, one of the prediction of general relaivity.

Re:tachyon

[maroberts]

Then the blind men drew their swords and shot each other in the back, right?

It explains how Han managed to shoot first.

Uh..Relativity didn't disprove Newtown

[Ronin Developer]

Newton's Law of Gravity showed that the force of attraction was proportional to the masses of the objects and inversely proportional to the distance squared: Fg=kM1M2/r^2

Einstein demonstrated in his experiment, through gravitational lensing effect, that mass bends space-time and his famous equation showed mass and energy to be equivalent. This effect, not normally observable in our daily lives, shows that Newton's law is still correct. It's at relativistic speeds and at the quantum level that other terms introduced by Einstein's equations become relevant.

Under normal conditions, we can not see the effect that Einstein predicted.

We did similar calculations using Quantum mechanics to derive other classical laws. It was, fascinating, to see how they hold up.

Re:It's still accepted...

[Gavagai80]

An approximation for certain contexts, which happen to be the common ones in our everyday experience. Newtonian physics is wildly wrong on some things further from our regular experience.

Re:tachyon

[itsdapead]

Lorenz contraction, says the tachyon.
Why the long face? asks the barman.
A tachyon walks into a bar.

95 years?

[rmandevi]

95 years according to which frame of reference?

The poetry of the Universe

[wjcofkc]

When contemplating phenomena in this universe, I find that in a small number of situations, a rudimentary understanding can be more readily had by a humble and feeble intellect such as mine if I simply drop the speed of light squared from the equation. C squared is where things get strange. Consider the following: A star 100 million light years away ignites. From out relative position and motion, we measure the light as traveling at ~186,300 miles per second over a distance of 100 million light years. As far as we are concerned, it took a long time to get here. Now for the tricky part. As everyone here I am sure knows, time slows down the closer you get to the speed of light, coming to a standstill once the cosmic speed limit is reached. As a consequence, as soon as the light from that star was generated, it was instantly already here. From our perspective, it took 100 million light years to get here. For the perspective of the light itself (so to speak), the transit time was 0. Apply that to light that is older than the Earth and it becomes a real mind-fuck. In fact, kick back and expand on that concept in many different ways. At least this is according to Dr. Tyson. Despite the complexities, E = MC squared is elegant mathematical poetry.

Re:The poetry of the Universe

[Primate Pete]

Also, since electrons do not experience time (as you stated), then NOTHING ever happens to them. Ergo, it is boring to be an electron.

That was the point, right? Mind-blowing = infinitely stultifying?

Re:I don't believe in relativity

[Eunuchswear]

Don't tell the fundies that, maybe they'd stop breathing.

Uh, hang on a minute, let me rephrase that... ... Please tell the fundies that, with luck they'll stop breathing.

Re:I don't believe in relativity

[RabidReindeer]

Nobody ever talks about Methusaleh's twin, Rodney Shortlife.

Re:I don't believe in relativity

[Jason Levine]

Everyone knows that God is everywhere at once. How is this possible? He's travelling really, really fast. This means that there's some massive time dilation going on. So obviously what was "six days" for him was billions of years for the rest of the Universe.

In all seriousness, though, the next time someone tells me that X can't be true because it's not in the bible, I'm going to pull out my smartphone and ask where smartphones are in the bible. Or computers. Or integrated circuitry. Then, I'll play some Angry Birds on my obviously non-existent smartphone.

was it 1922 eclipse that provided solid data?

[k6mfw]

PBS program on Einstein mentioned images and calculations from 1919 eclipse was doubtful. Some claimed it did not show bending of light (star positions still where they should be) but others said, "not so fast." It was 1922 which William Campbell got beautiful images of stars around the eclipsed sun, observed 92 stars observed positions from where they should be. Campbell's first telegram was to Albert saying these images and calculations definitely support his theories. Of course it was not easy for Campbell, his first solar eclipse expedition in 1914 went bust at outbreak of WWI, and following attempts in later years were not good. It was 1922 which Campbell got great images while everyone else (and there were several) either got weathered out or had poor techniques. Another fascinating talked about in this PBS program was after WWI Germans were hated by Brits, French, Americans but Einstein was very welcomed and was a huge "rock star" where all these people wanted to meet him, get autographs, get pic taken with him. Even though virtually all don't understand theory of relativity.

I am not a physicist but I'm confused

[UnknowingFool]

I thought the 1919 solar eclipse was the first confirmation of General Relativity not special relativity (E = mc^2).

Irony

[doug141]

That article at slate did not address the possibility of the universe being such an isolated system. It seemed to be an angry rant by a physicist who was mad at other scientists for not sharing his views on the material world and consciousness.

Re:The irony of the 1919 data is overwhelming

[Anonymous Coward]

This is coming from a man who failed his PhD thesis more than once due to algebraic errors and other sloppiness.

While he did make an algebraic mistake in his thesis, he was awarded his PhD in 1905, and his correction was not made until 1911. He didn't fail the doctorate program, let alone multiple times.

Re:tachyon

[OutOnARock]

I believe it goes something like this....

One bright day in the middle of the night

Two dead men got up to fight

Back to back they faced each other

Drew their swords and shot each other

And if you think my tale is tall

Ask the blind man, he saw it all

You conflate correlation with causation.

[Anonymous Coward]

It is also possible that the universe has determined, or more correctly caused, both the particle's state and your actions.In other words the cause is in the past of both the particle's current state and your actions. That is why they are correlated, not because either causes the other, but because both are caused by what has happened in the past.

A key logical error is in thinking that anything at all is outside the system and yet still interacts with it. Another key logical error is thinking that we can actually isolate parts of the system.

We are all connected man.

Re:I don't believe in relativity

[dfsmith]

God could also have a really well defined momentum, and therefore the uncertainty inequality makes Him omnipresent.

95 years? Must not have gone to a public school

[guruevi]

Newtonian gravitation was still being taught at my high school less than 20 years ago.

Re:The irony of the 1919 data is overwhelming

[themusicgod1]

Relevant LessWrong: "If Einstein had enough observational evidence to single out the correct equations of General Relativity in the first place, then he probably had enough evidence to be damn sure that General Relativity was true."

Re:The irony of the 1919 data is overwhelming

[Yevoc]

He didn't fail the doctorate program. He failed his defense. Three times.

Re:The irony of the 1919 data is overwhelming

[Yevoc]

The point is that he had enough hubris to believe that general relativity worked up to cosmic scales without any error. The fact that there was in fact a substantial amount of experimental error, some of which didn't add up, didn't disturb him in the least.

General relativity actually does have problems on the cosmic scale, which is what led Einstein to introduce the cosmological constant, amongst other things. (Today people still don't know if/how general relativity holds in some places in the cosmos, ironically enough right next to a large star is one of them, kind of like the 1919 measurement) Between the arbitrary cosmological constant and his undying disbelief in quantum physics, you can see he had a disdain for reality and instead preferred the fiction inside his head.

I wouldn't harbor so much venom for the man if he hadn't become such a celebrity with this kind of behavior (which of course is something he actively pursued and enjoyed).

Re:The irony of the 1919 data is overwhelming

[Yevoc]

Whoever modded this down really succeeded in pissing me off. This is the last time I bother making posts to scientifically-illiterate code monkeys who are clearly the same Einstein worshippers I abhor. Bye.