## Stellar Trio Could Put Einstein's Theory of Gravity To the Test 106

Posted
by
samzenpus

from the there's-a-first-time-for-everything dept.

from the there's-a-first-time-for-everything dept.

sciencehabit writes

*"In a cosmic coup, astronomers have found a celestial beacon known as a pulsar in orbit with not one, but two other stars. The first-of-its-kind trio could soon be used to put Einstein's theory of gravity, or general relativity, to an unprecedented test. 'It's a wonderful laboratory that nature has given us,' says Paulo Freire, a radio astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany, who was not involved in the work. 'It's almost made to order.'"*
## Re:If only /. beta was tested as much as Einstein (Score:5, Insightful)

Isn't that the point of a Beta release? To obtain feedback and to fix what isn't right with something?

## Re:If only /. beta was tested as much as Einstein (Score:4, Insightful)

## Re: (Score:2, Insightful)

True. That should never have made it to the beta stage.

More importantly, a beta should be to get feedback, and aside from writing comments in articles that have nothing to do with it, I see no obvious feedback forum.

## beta feedback (Score:4, Informative)

## Re: (Score:2)

on top left of the main site there's a link to

http://www.surveymonkey.com/s/sdredesign [surveymonkey.com]

Oh yes, with such unbiased options as:

How do you like the look and feel of Slashdot Redesign compared with the classic Slashdot site (www.slashdot.org)?

Significantly better

Better

About the same

Not as good.

Which leads to "Well many [2] of our readers thought the site was significantly better, but the worst response was it wasn't quite as good as the old one"

## Re: (Score:2)

It's an imperfect system but it's still a system.

## I quite like it (Score:2)

much more modern looking, it works fine for me. I can reply to stuff, understand the threading and generally it works just great.

## Will be interesting ... (Score:5, Interesting)

## Re:Will be interesting ... (Score:4, Insightful)

Meh, just simulate it. No need to solve the equations, and simulating it isn't very hard. We have computers now, they are good at this.

But how do you know if your simulation is correct?

Anyone could easily write a sim that has three stars and they all coexist, happily passing through each other or something ridiculous. The point here is that we can see if the Theory and any simulations match the real world.

## Re: (Score:1)

Yes, you compare the simulation to the observations. I suppose I didn't explicitly state that, but I assumed it was obvious. My point is theres no need for hard math, just see if a simulation matches reality. N-body simulation is trivial: I wrote one in middle school. A relativistic one is only slightly harder. This one is likley gonna need tidal forces and other tedium too, but thats another issue.

My main point was "n-body calculations are hard enough with Newtonian physics. The "Einsteinian physics" calcu

## Re: (Score:1)

If you compare your simulation result to reality and you do not know if your simulation follows the theory you can not conclude anything.

## Re: (Score:1)

His point is that it is easy to write some n-body simulation, but it is much harder to write one that gives correct results, and to prove that it follows the theory. The one you wrote in middle school probably didn't give correct results, or could you reproduce for example constant orbits in a two body problem?

It's just a bloody simple system of differential equations. n bodies, each has a location (3 coordinates) and a speed vector (3 coordinates), so you have six equations. The speed is obviously the derivative of the location, and the theory gives you the equation to calculate the derivative of the speed. Look up Fehlberg or "Adaptive Runge-Kutta-Fehlberg" and you are there.

## Re:Will be interesting ... (Score:5, Insightful)

It's just a bloody simple system of differential equations. n bodies, each has a location (3 coordinates) and a speed vector (3 coordinates), so you have six equations. The speed is obviously the derivative of the location, and the theory gives you the equation to calculate the derivative of the speed. Look up Fehlberg or "Adaptive Runge-Kutta-Fehlberg" and you are there.

That's Newton.

With relativity things get hard, quick. Both time (thus, speed) and space (thus, speed and distance) dilate, mass changes (thus, the attractive forces between bodies and thus their acceleration, and thus their speed, and thus their location), and some other oddities.

## Re: (Score:2)

That will give the wrong answer. The reason is step size. Remember the relative positions are constantly changing, except for certain special cases.

FWIW, professional astronomers can't do an accurate model of the solar sysstem. The can do one that's "almost correct", but that's not the same. And the solar system can be handled with Newtonian mechanics. Once you bring in pulsars emitting gravity waves...

Yi!P.S.: IIRC, the best models of the solar system can't predict on which side of the sun the earth

## Re: (Score:3)

And how do you know if your equations are correct?

Anyone could easily write an equation that equates the living hell out of the three bodies, putting them in some absurd relation to each other. Does it say anything about reality? Nah.

## Re:Will be interesting ... (Score:4, Informative)

And how do you know if your equations are correct?

That's the whole point raised by TFA. You know your equations are correct if the results of the simulation agrees with the results of the observation.

This system offers an unprecedented way to check how much does model general relativity fit the actual universe.

It's all in TFA, but I suppose reading it breaks the slashdot rules. Since we have three stars that are much more massive than any other three body system observed before, we can make measurements of the effects of gravitation with more precision, because the effects of those three stars on each other are so much bigger than the perturbations from other masses.

## Re: (Score:2)

Doesn't it come down to "do your equations match reality?"

I'm pretty sure they're not just going to come up with an equation and say "see, done" -- they're going to make sure it matches up with what we observe.

You know, empirically either validate or refute the equations.

## Re: (Score:2)

How does that not apply to simulation? Or didn't you bother to read the thread?

## Re: (Score:2)

I did, but it's one thing to have calculations, it's another thing to run a simulation, and it's yet another thing to be able to compare those to an actual system and see if your results stack up.

As I understood this, this is the first time someone will be able to actually validate the equations and simulations against something real.

## Re: (Score:2)

I still have nightmares from my Electromagnetism III class.

## Re: (Score:1)

## Re: (Score:1)

## Re: (Score:2)

n-body calculations where n>3 are all simulations. Anyone coming up with a mathematical solution to such a system is in line for a Nobel prize.

The trick is to remember there are no real three body systems in the entire universe...

## Re: (Score:2)

n-body calculations where n>3 are all simulations.

I was going to say, I can solve plenty of N-body calculations where N = zero.

(I think anyway. I'm a biologist not a mathologist. Maybe N = zero is a real thing that isn't simply "zero." If so, I sincerely apologize and accept my punishment.)

## "A violation would be a complete revolution." (Score:5, Interesting)

The summary is light on any details, so here:

The distinctive new system opens the way for testing a concept behind general relativity known as the equivalence principle, which relates two different conceptions of mass. An object's inertial mass quantifies how it resists pushing or pulling: It's easier to start a stroller rolling than a car because the stroller has less inertial mass. A thing's gravitational mass determines how much a gravitational field pulls on it: A barbell is heavier than a feather because it has more gravitational mass.

The simplest version of the equivalence principle says inertial mass and gravitational mass are equal. It explains why ordinary objects like baseballs and bricks fall to Earth at the same rate regardless of their mass—as legend claims Galileo showed by dropping heavier and lighter balls from the Leaning Tower of Pisa.

The strong equivalence principle takes things an important step further. According to Einstein's famous equation, E = mc2, energy equals mass. So an object or system's mass can be generated by the energy in the gravitational fields within the system itself. The strong equivalence principle states that even if one includes mass generated through such "self-gravitation," gravitational and inertial mass are still equal. ...

By tracking the system's evolution, Ransom and colleagues should be able to tell whether either the inner white dwarf or the pulsar falls faster toward the outer white dwarf and test strong equivalence about 100 times as precisely as before, Damour says.

"Gravitational Field"... space-time curvature "field"? Uhm, "gravitational mass" vs "inertial mass" equivalence... "explains why" o_O?

Shh!The astrophysicists are over.Don't mention the Higgs!In all seriousness, we know damn well Einstein's equations are simply better approximations / explanations than Newton's approximations are -- It's only a matter of time before we prove them "wrong" (but still damn good and useful approximations, like Newton's) -- We just need some elusive experimental evidence to prove it, and this could be it due to the large gravitational coefficients and a steady measurement scale provided in the pulsar. That is, unless Einstein's approximation turns out to be more accurate than our observations of this system. It shouldn't be any more of a "revolution", as TFA states, if the observations prove to be in violation of the equations: We should be trying to find better equations anyway thanks to that whole Standard Model thing, and we are. Physics seems to goes through these periods where a bunch of new theories explain various things to a precision, the precision is surpassed in observations, and then someone like Newton, Einstein, Feynman, Hawking, etc. comes along and presents elegant / unifying equations to explain the disparate pieces better. Looks like we're still in the middle of the very important prove old-theories "wrong" (read: inaccurate, conflicting with some observations) and scratch our head over tests for new hypotheses to fit more accurate measurements stage.

## Re: (Score:1)

## Re: "A violation would be a complete revolution." (Score:1)

vortexcortex.com is obviously a domain name. Duh.

## Re:"A violation would be a complete revolution." (Score:5, Insightful)

Yeah, that sort of sounds like a bunch of late-night-I've-got-the-munchies BS.

FTA: "Paulo Freire, a radio astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany... says a violation would be 'a complete revolution.'"

No offense, but I'm going to trust the astronomer at the world-renowned scientific institute over the indie-game artist on this one.

## Re: (Score:2)

I'd have to read TFA (shudder) to see if the astronomer backed up his statement, but an astronomer simply saying "This is revolutionary!" would be less convincing than what VortexCortex posted if that's all there was.

## Re: (Score:3)

## Re: (Score:3)

That is, unless Einstein's approximation turns out to be more accurate than our observations of this system.

Err, umm, "accurate", when it comes to predictions of scientific theories, means "closely matches the observations", so a theory can only be "more accurate than our observations of this system" if the observations in question are wrong and

subsequentobservations, determined to be (more) correct, are better matched by the predictions of the theory. Is that what you mean here?## Re: (Score:2)

Wait just a nanosecond. I'm just a self educated layman, but didn't Einstein come up with an explanation for how gravity works (mass distorts space-time)? Whereas Newton believed gravity worked because...what? Einstein did a lot more than just come up with a better equation didn't he? Heck, even the concept of space-time is very important concept, that, while illustrated through equations, took us far beyond the Newtonian understanding of the Cosmos. It's much more than just refining the math. Don't y

## Re: (Score:2)

Actually, AFAIK we don't know that Einstein's equations are wrong at all. That's a surmise. (Yes, there's something wrong somewhere, but it may not be GR.) It may well be true, and we won't know until we find discrepancies. That's what this astronomical research is for. Without discrepancies, about all we can say is that GR accounts for the observed facts and is mathematically elegant, and looking for new equations is speculative at best.

## Delicious (Score:5, Funny)

In a cosmic coup, astronomers have found a celestial beacon

Mmm...cosmic soup with bacon!

## Re: (Score:2)

Everything in celestial terms is much, much bigger. Therefore, I'd expect celestial bacon to be five light years across and twenty five light years long.

## Re: (Score:2)

You don't know what you are talking aboot eh!?!

## Is (Score:1)

Ok, help my layman ass out here. IIRC, according to Einstein, acceleration and gravity aren't just similar phenomena, but are the exact same phenomena, and, since you are always travelling at c through the combined spacetime continuum, which gravity warps, the gravitational pull is you actually accelerating through this warped spacetime.

That seems way too freaking cool to fail at some umpteenth decimal.

## No (Score:1)

... since you are always travelling at c ...

Light travels at c in a vacuum and anything with mass does not. Be wary of anyone who tells you otherwise.

(I'm a physicist)

## Re: (Score:1)

So...are acceleration and gravity the same phenomenon under relativity?

## Re: (Score:2)

Ok, help my layman ass out here. IIRC, according to Einstein, acceleration and gravity aren't just similar phenomena, but are the exact same phenomena, and, since you are always travelling at c through the combined spacetime continuum, which gravity warps, the gravitational pull is you actually accelerating through this warped spacetime.

That seems way too freaking cool to fail at some umpteenth decimal.

I've always found the feeling associated with thinking about the Principle of Equivalence to be exquisite — wistfully thinking something beautiful would be lost if (or when) it was disproven.

## Re: (Score:2)

He's probably insisting on a more direct form of observation, even though he actually knows this is impossible. (Well, perhaps not, if the new lens design that allows one to see things fractions of a wave length long can be built at the right wave length. I've got my doubts...and even then the wavelength would be too short to see directly.)

OTOH, I'm also not very pleases with the quality of the evidence that we need to deal with, and would like something a lot less indirect. But right now that's the bes

## Re: (Score:1)

The only difference between physics and religion though is the fact that the 'temple' built to it is there to test to see if predictions made by the standard model are in fact correct, or if the theory needs revision. You will not see anything along those lines in a religion.

## Re: (Score:2)

The only difference between physics and religion...There is nothing whatever that physics and religion have in common. Physics is the study of the physical universe, religion is not about the physical universe at all.

## Re: (Score:2)

Sorry, but though the claim was made General Relativity didn't predict the correct deviation of Mercury's orbit. The key turned out to be the flattening of the sun at the poles. (I think once that was taken into account, General Relativity gave a better answer than Newton, but the Newtonian answer was good enough that it wouldn't have been noticed originally.)

## 'It's almost made to order.'" (Score:2)

Whose to say it wasn't? Maybe some advanced civilisation built it to test just this principal. Maybe we are simply looking over the shoulder of someone else's work. How do they correctly reference that in the eventual paper? :-)

Bob.

## can someone explain this? (Score:2)

## Re: (Score:2)

## There is a God after all? (Score:2)

"Made to order?" Hmm, so the creationists are right after all. There is a creator and he clearly likes science...

Could have been worse I guess.

## Re:Happy Sunday from The Golden Girls! (Score:5, Funny)

Your heart is true, you're a pal and a cosmonaut.God dammit I keep seeing this posted here over and over with the same error every time. Every time!

It's "you're a GAL" you dipshits!

## Re: (Score:2)

What the heck do exchange address lists have to do with anything?

## Or (Score:2)

## It's Ether time (Score:2)

## Re: (Score:2)

I'm sorry, I cant tell if your a targeted spambot or serious.

## Re: (Score:2)

It's the Electric Universe folderal again, I think. Better than arguing with the people who believe in 'morphic fields', but not much.

## Re: (Score:2)

IIRC though (this is several decades ago) you only get the simplified form by dropping higher order terms. There was a good reason to do so (IIRC they were *extremely* small in value), but it does mean that it's an approximation. However, since even the deviation of Einsteinian theory from Newtonian is difficult to detect, I expect that the corrected version would differ from the Einsteinian version to such a slight degree that it would still be impossible to detect. And (again, IIRC) there was an infini

## Re: (Score:2)

Thanks. As I said, it's been a LONG time since I did this.

## Re: (Score:2)

I completely agree with you about the ether, and in fact I just posted such a comment [slashdot.org] before I read your comment.

I look forward to reading more about your theory and humbly offer my own [just-think-it.com] for your consideration.

Best,

Floyd