I Is there an experimental proof that an Earth/Moon barycenter exists?

[Nugatory]

In any case, my question is simple: does anyone know of any experiments or observations that PROVE the Earth and Moon rotate around a barycenter? Yes or no?

@romsofia has pointed you at the lunar ranging measurements and @hutchphd has pointed out that we have successfully navigated spacecraft from the surface of the Earth to where the surface of the moon will be if the two bodies are orbiting their barycenter.

 

[Bandersnatch]

Yeah, so this does definitely show in ephemerides, since ignoring the barycentric motion when measuring parallax of a hypothetical stationary object at 10 AU over the base of a fortnight's worth of orbit would introduce an error on the order of 1 arcsecond vs ~miliarcsec or better accuracy of modern ephemerides.

So each time anyone uses ephemeris tables (or software, these days) to point their telescope at a solar system object and find it where it's supposed to be, they provide evidence of the kind required by the OP.
Whether this will be accepted as such by the OP is another matter.

 

[Orodruin]

Frankly, I would have expected a Mensa group to include people who understood basic physics and the well known dead-end that is push-gravity.

Frankly, I would have expected a Mensa group to understand how limited and pointless of a request the measurement of the Earth-Moon barycenter is...and of course someone in the group to understand the scientific method itself, and teach it to the rest of you.

If this is representative of Mesa, I'm not impressed.

My personal experience (that admittedly is over 20 years old) is that it is representative. I was a member for a year or so, but most people I interacted with and the local monthly publication gave the impression of people who somehow thought that having a (relatively) high tested IQ (it is not *that* high) made them superior and that any thoghts they had on things they were ignorant about would be pure gold.

 

[Orodruin]

My problem with our current understanding of gravity started with that blasted simulation of the mass of the Earth warping space/time to create gravity. You know the one. It looks like a bowling ball on a sheet of rubber with a satellite falling into the well that creates an orbit around the bowling ball. I have at least two problems with this:

The first is how this scenario would allow satellites to orbit in something other than an equilateral plane around the mass depending upon their weight when they fell into the well. The heavier the satellite the lower in the well they would orbit. Which does not relate to the real world since all orbits around the Earth can only occur when the orbit is centered over the mass of the planet. You cannot have a satellite orbiting above the tropic of Capricorn, for example. Which could happen with the simulation mentioned previously.

Ok, I am going to be pretty blunt, but I think it is necessary here:

So, you have made a number of serious errors here. First of all, the image you are talking about is not a simulation - it is an illustration. Second, it has nothing at all to do with Newtonian gravity - it is an analogue used to popularize general relativity. Third, it is, as most popularizations, an oversimplified image - it has very little to do with the actual description of gravity in GR, it just illustrates curved space. Fourth, you have taken this popularized image way too literally and made your argument based on this.

Each of these errors is a direct killer for any serious argument being made. If you want to have any chance of making a serious argument you need to learn what the theory you are trying to disprove is actually saying, not base your argument on a popularized image from which you have made erroneous extrapolations about what the theory actually says.

 

[PeroK]

The only thing I am seeing that we don't have the technology to detect it and that I should just accept that it is there without proof just like everyone else. Which is bogus.

The barycentre of any system of particles is not a physical thing. You can't detect it. You can measure where each particle in the system is, measure the mass of every particle in the system and then compute where the barycentre is. For example, if you and your friend drive your cars around, then the barycentre of that two-body system will be roughly half-way between your cars (assuming they are of approximately equal mass). But, no one is going to be able to stand by the side of a motorway and "detect" the barycentre of that system! What would they detect that would tell them that a point on the road is half-way between your cars? Every pair of cars (every pair of objects) has a barycentre. How would they distinguish one "detected" barycentre from another?

In short, the barycentre is a geometrically defined point in space, but there is nothing there to identify it as such. It doesn't exist, because it is purely geometrically defined. There is nothing physical at the barycentre.

I was recently looking at a problem involving the orbit of Mercury round the Sun. All the data is there:

https://en.wikipedia.org/wiki/Tests_of_general_relativity#Perihelion_precession_of_Mercury

No one is asking you to believe that Mercury orbits the Sun in an ellipse without proof. The data has been maintained for centuries. But, the ellipse precesses to a degree that the Newtonian model cannot explain. The Newtonian model almost exactly predicts the relative position of the planets of the Solar system over time. But, there was always a doubt over the precession of Mercury. In a way you can't ask for more than that. That is the way science works. That is the way physics is done.

And, of course, General Relativity trumps Newtonian gravity by predicting the additional observed precession of Mercury. That is the way science progresses.

 

[Vanadium 50]

So, you have made a number of serious errors here.

Let's keep going.

Fifth, you still haven't given a clear description of your point. Are you arguing that the gravitational force is not-central? Or are you arguing that it is not linear? Both are wrong, but you seem to have them tangled up. Sixth, you are giving as evidence for your point that you are really, really good at things like multiple choice tests and word analogies.

 

[Orodruin]

Or are you arguing that it is not linear? Both are wrong,

Well, the EFEs are non-linear ...

 

[OmCheeto]

Would that be measurable? Actually, the shift in Earth's position is not that much less than its diameter so maybe not so daft after all. A few thousand km relative to a distance of a few hundred million km. That's around 10^-5 radians which is no problem for astronomers. Edit: well, errr measuring stellar distances in parsecs relies on the full AU.
But I see @OmCheeto has beaten me to it and Mars would be the obvious choice.

According to my back of napkinish attempt so far, the first serious problem is that the Earth travels the distance of the barycenter offset in only 160 seconds. I'm starting to understand why no one would want to tackle this problem. And given that I can identify only 2 stars in the sky, this is well beyond my present capabilities.

 

[Vanadium 50]

Let me keep going. Sixth, if you did your homework and Googled "push gravity", the very first link you would get is a Wikipedia article on what is commonly and erroneously called LeSage gravity. It's 430 years old and known to be wrong for well over a century. Either the OP didn't bother to look it up, or you did and decided to post anyway. I'll let the OP decide for himself which is better. Seventh, tossing around words like "bogus" is unlikely to win friends and influence people. Ignorance per se is not a problem - we all have things we are ignorant of. Being ignorant and judgemental is a different kettle of fish.

 

[Ron Hargrove]

In your mensa group has anyone defined what is required to "prove" the existence of a barycenter? Operationally it is not clear to me how such a proof would be undertaken to your satisfaction.

No. This was just in casual conversation. I would assume that if the EM were rotating around a barycenter it would cause some sort of observable deviation from a smooth transit across the sky for, at least Mars and Venus. My friend was actually writing her doctoral thesis on gravity being a push force and not a pull force but never completed it. She has some of the same questions about the current concept of gravity that I do which led me here.

 

[PeroK]

No. This was just in casual conversation. I would assume that if the EM were rotating around a barycenter it would cause some sort of observable deviation from a smooth transit across the sky for, at least Mars and Venus. My friend was actually writing her doctoral thesis on gravity being a push force and not a pull force but never completed it. She has some of the same questions about the current concept of gravity that I do which led me here.

The answer is:

$$ds^2 = -(1- \frac{2M}{r})dt^2 + (1 - \frac{2M}{r})^{-1}dr^2 + r^2d\theta^2 + r^2\sin^2 \theta d\phi^2$$

 

[Ron Hargrove]

No. This was just in casual conversation. I would assume that if the EM were rotating around a barycenter it would cause some sort of observable deviation from a smooth transit across the sky for, at least Mars and Venus. My friend was actually writing her doctoral thesis on gravity being a push force and not a pull force but never completed it. She has some of the same concerns about the current concepts involving gravity that I do which led me here.

Of course, a barycenter is not a measurable point. But rotating around a barycenter would cause a "wobble" as the Earth rotates around that barycenter as it chugs along in its orbit which I feel should be able to be detected somehow. Yet again, I am only trying to find out if anyone is aware of any experiments that clearly show that the Earth is, in fact, rotating around an EM barycenter or is it just universally accepted as valid without being proved that it occurs?
Let me get to the crux of the issue. Two objects with mass are floating in the weightless vacuum of space. If they are near enough to each other they will move toward each other. How do you know it is an invisible force pulling them toward each other instead of an invisible force pushing them toward each other?
I realize that I am no expert in astronomy or physics which is why I came here to seek the council of people who are.
Thank you all for your input.

 

[Ibix]

My problem with our current understanding of gravity started with that blasted simulation of the mass of the Earth warping space/time to create gravity. You know the one.

The problem with the "curved sheet" model is that the Earth only holds the moon in place because that diagram sucks so much. It's a very poor illustration of our actual models (a case of drawing what can be drawn, rather than explaining what's important). It looks nice and superficially comprehensible, though. And, as @Orodruin notes, it's talking about general relativity, not Newtonian gravity.

Let's keep going.

Fifth, you still haven't given a clear description of your point. Are you arguing that the gravitational force is not-central? Or are you arguing that it is not linear? Both are wrong, but you seem to have them tangled up. Sixth, you are giving as evidence for your point that you are really, really good at things like multiple choice tests and word analogies.

Furthermore, there's a thorny question of what OP actually means to consider. The planets follow the paths they follow. Breaking their motion up into "orbit around the Sun" plus "orbit around barycentre" plus "effect from oblateness of Sun" plus "effect from Jupiter" plus, plus, plus is very much a human convenience. I'm not sure how you could remove "orbit around barycentre", except to set the Moon's gravitational effect to zero in your model (which, I think, is broadly what @Bandersnatch's order of magnitude estimate of parallax implicitly does). Presumably OP's contention is that this would have zero effect on predicted astronomical observations, and presumably the tides happen for some other reason unrelated to the Moon's gravity.

 

[Ron Hargrove]

Let me keep going. Sixth, if you did your homework and Googled "push gravity", the very first link you would get is a Wikipedia article on what is commonly and erroneously called LeSage gravity. It's 430 years old and known to be wrong for well over a century. Either the OP didn't bother to look it up, or you did and decided to post anyway. I'll let the OP decide for himself which is better. Seventh, tossing around words like "bogus" is unlikely to win friends and influence people. Ignorance per se is not a problem - we all have things we are ignorant of. Being ignorant and judgemental is a different kettle of fish.

The "bogus" part referenced accepting an idea just because everyone else does without proof that it is valid. That is how everyone came to believe the Earth was the center of the universe.
Your post has led me to learn of the Richard Feynman examined the Fatio/Lesage mechanism which may give me the answer I am looking for.

 

[Ron Hargrove]

My personal experience (that admittedly is over 20 years old) is that it is representative. I was a member for a year or so, but most people I interacted with and the local monthly publication gave the impression of people who somehow thought that having a (relatively) high tested IQ (it is not *that* high) made them superior and that any thoghts they had on things they were ignorant about would be pure gold.

That has not been my experience. While there are a few Mensa members around with delusions of superiority the vast majority are just common folks with brains that won't shut down or notice immediately when things don't add up. I like to say that a Mensan is just as likely to leave the house with their fly open as anyone else.

 

[PeroK]

The "bogus" part referenced accepting an idea just because everyone else does without proof that it is valid. That is how everyone came to believe the Earth was the center of the universe.

Let me be honest. We've tried to answer your questions, but all you do is repeat your unwarranted assertion that the rest of us just swallow what we are told without proof. It's so insulting.

Like a previous poster said, it is like Mensa has hoodwinked you into thinking you are a being with a higher intelligence. And, although we slog away at learning and understanding the physics and mathemetics, all it takes is a casual conversation between you and your friend to blow apart everything we know and replace it with half-baked ideas that have no mathematical or experimental support.

It ain't that easy!

If you have any real intelligence you have to realize how absurd your world-view has become.

 

[Ron Hargrove]

Yet again, my only question was whether anyone reading this thread was aware of experimental proof that an EM barycenter exists instead of just the theory that an EM barycenter exists which does not appear to exist to the knowledge of anyone who has read this thread.

 

[Ibix]

which does not appear to exist to the knowledge of anyone who has read this thread.

Huh? Bandersnatch provided it this morning! Back of the envelope, neglecting barycentric movement, stuff would be misplaced on the sky by around a thousand times the error on published tables.

 

[Ron Hargrove]

Huh? Bandersnatch provided it this morning! Back of the envelope, neglecting barycentric movement, stuff would be misplaced on the sky by around a thousand times the error on published tables.

What I am looking for is historically verified observations that prove a barycenter rotation and not calculated and projected tables.

 

[PeterDonis]

I and at least one other Mensan in my local group (yes, I am a member) have been pondering whether or not gravitation is actually a 'push' force and not a 'pull' force.

PF is not for discussion of personal speculation or past attempts at theories that have already been thoroughly debunked (of which "push gravity" is an example).

What I am looking for is historically verified observations that prove a barycenter rotation and not calculated and projected tables.

And you have been given multiple examples of such in this thread. You said you came here looking for input from experts. You got it. If you don't want to accept it, that's your problem, not ours.

 

[Nugatory]

Yet again, my only question was whether anyone reading this thread was aware of experimental proof that an EM barycenter exists instead of just the theory that an EM barycenter exists which does not appear to exist to the knowledge of anyone who has read this thread.

Huh? Various posters in this thread have mentioned lunar ranging, spacecraft navigation, and that planets appear where ephemerides calculations say they should be. All of these are observations showing that the barycenter exists. (There are also observations of double stars, which clearly orbit their common barycenter - it would be a strange universe indeed if gravity between stars worked differently than gravity between planets).

But even if none of that experimental evidence existed it would be mistaken to say, as you do in the first post and later, that the existence of the barycenter would be “just assumed”. The scientific claim about the barycenter is “If our current theories about gravity accurately describe the universe, then there is a barycenter”, and the existence of the barycenter is not an assumption, it is a deduction as solid as “if Euclid’s axioms are valid, then the interior angles of a triangle add to 180 degrees” - the conclusion follows inevitably from the premise.

Thus, any challenge to the notion of the barycenter is actually a challenge to the premise “our current theories about gravity accurately describe the universe”. That is, are there observations that disagree with the predictions made by our current theories about gravity? In the absence of such observations , I don’t need observational confirmation of the barycenter (although as noted above, there is an abundance of these) to conclude that it exists. It’s as valid a claim as the (completely untested) proposition that the next time I drop an object, it will fall just like the last time.

 

[PeterDonis]

The OP question has been thoroughly answered. Thread closed.