# Michelson Morley experiment and heliocentrism

#### Amok

Hello,

I just heard a guy talking about the Michelson-Morley experiment as evidence that the earth is still. It is true that the MM experiment basically showed that the earth was at rest with respect to "the ether" (but we know that the earth moves around the sun, so the notion of ether starts looking a bit flimsy). This guy basically said that this showed that the earth was completely stationary and used it to defend geocentrism. How do you show that the earth is indeed moving around the sun? I've read about stellar aberration, but can you guys suggest some less complicated arguments that I can give to people like this (I haven't studied astrophysics, so I'd be cool if you explain this stuff to me as well)? I guess that if you could repeat the MM experiment on Mars, it would also show that Mars is "stationary", but we know that it is in relative motion to the earth. I guess no one has done that experiment on Mars though.

#### Simon Bridge

Homework Helper
Hello,

I just heard a guy talking about the Michelson-Morley experiment as evidence that the earth is still. It is true that the MM experiment basically showed that the earth was at rest with respect to "the ether"
Yep.
(but we know that the earth moves around the sun, so the notion of ether starts looking a bit flimsy). This guy basically said that this showed that the earth was completely stationary and used it to defend geocentrism. How do you show that the earth is indeed moving around the sun?
There is quite a lot - you can read up about luminiferous ether theories online.

I've read about stellar aberration, but can you guys suggest some less complicated arguments that I can give to people like this (I haven't studied astrophysics, so I'd be cool if you explain this stuff to me as well)? I guess that if you could repeat the MM experiment on Mars, it would also show that Mars is "stationary", but we know that it is in relative motion to the earth.
That's correct - or even the Moon.

You get the result because the speed of light is the same for all observers. So you could load the MM apparatus onto a truck and drive it at a constant speed and you'd get the result that the truck is stationary.... but you are sitting their driving it.

Unfortunately these people do not have rational reasons for their beliefs so you cannot use mere science to contradict them. OTOH: by arguing with them in front of an audience you may stop them convincing others and spreading their junk science.
http://www.evidencechart.com/charts/10 [Broken]

Heliocetricism rest on an accumulation of evidence:
Look up:
1- Stellar aberration.
2- Stellar parallax.
3- The Doppler Effect.
4- Retrograde motion of planets.
5- Phases of Venus.

Basically it ends up surviving Occams Razor.

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#### Amok

Yes, I understand the postulates of relativity, but I'm not to good at astronomy. And in the case of MM, the movement of the earth around the sun is assumed in order to draw the conclusion that the ether does not exists (or always moves with the earth). This guy is attacking the assumption that the earth moves around the sun in order to attack relativity (but when he talks about relativity I can immediately see he doesn't understand much about the subject, he mixes special and general relativity for example). I'm gonna read up on this stuff though. Thanks for the reply.

#### micromass

What about all the spaceships that have been succesfully sent to other planets? We could only have done that if our understanding of the mechanics of the solar system was sufficiently accurate.

Or does the guy also deny the existence of spaceships and of the moon landing??

#### Amok

What about all the spaceships that have been succesfully sent to other planets? We could only have done that if our understanding of the mechanics of the solar system was sufficiently accurate.

Or does the guy also deny the existence of spaceships and of the moon landing??
I dunno, I guess that is a very good point though :)

Here's a question though. We could, in principle, say that the earth is the center of the solar system (place ourselves in the reference frame of the earth), and the only effect this would have, is that other planets would have very weird orbits indeed (from a mathematical viewpoint). However, I think that heliocentrism is about a bit more than that, isn't it? Can someone explain this to me?

#### russ_watters

Mentor
I've heard a number of times that such a model could be built, but:
1. AFAIK, no one ever has.
2. It would reduce to the GR model anyway.

#### Amok

GR model?

Anyway, the earth is constantly accelerating which means there must be a way of showing it is moving, even if you place yourself in the reference frame of the earth (since it is non-inertial). You can use a foucault pendulum to show the earth is rotating upon itself, can you guys think of an experiment to show the earth is going around the sun (using fictious forces)?

#### Simon Bridge

Homework Helper
You can tell the Earth is rotating on an axis by observing rotation of the sky once a day but I could argue that the sky is the one rotating ... but observing how coriolis and centrifugal effects behave at the surface of the earth will tell you that either the surface is an accelerating reference frame or that Newton was wrong or that there are some weird extra forces around.

The accelerating reference frame is the simplest one that agrees with all the evidence.

The same arguments apply to geocentrisism ... you could, in principle, measure "circular motion" artifacts from the motion about the Sun but that could just mean the Earth is stationary and Scientists have been overlooking some sort of weird force all this time that just happens to act in the way that exactly mimics heliocenticism. [note: the soho satellites made use of the Earth orbital angular momentum to get where they are... that would be an equivalent to the Foucaults pendulum experiment on astronomical-unit scales.]

Similarly the geocentrist has to explain the weird orbits for the planets, the phases of Venus, and the success of space missions. But they could do this - eg. people were able to navigate great distances while believing the Earth was flat.

Note - it is not a easy as Newton thought to identify when you are accelerating - if you were in an enclosed box, is there any experiment you could do to demonstrate that the box (and you) were accelerating and the direction of gravity changing (say the box is tilting?) In fact - in free fall, you are accelerating, but can you do an experiment to show this?

But I imagine all this is a bit of a smoke screen because the person you are arguing with wants to say, not that geocentricism is correct, as such, but that relativity is wrong.

The motivation for this, I suspect, is that the person you are arguing with wants to say that the Bible is correct... many Christian creationists also like to thing in terms of biblical literalism and the bible says that the Earth is unmoving at the center of everything ... this is the One True Reference Frame. Even when they are not that literal, they tend to be opposed to "relativism" (because they know the One True Way - the idea that other Ways can be right is just plain wrong).

However, relativity seems to be saying that the nature of Creation itself is relative ... there are no One True reference frames anywhere. You can see how this could be quite upsetting to many people (and I apologize to those Christians, and creationists even, who do not think like this.)

The Geocentric model is just another reference frame - albeit a non-inertial one. Physically it is just as valid as any other one. The MM model does not show that this is the One True reference frame because exactly the same effect is observed from any other reference frame. There is nothing special that would produce anything different.

We teach helioenticism in schools because the kids don't have the math for changing reference frames and because we philosophically favor those propositions that require the least amount of extraneous assumptions.

BTW: Cliff Platt has an interesting take on this:
... basically, in order to argue that geocentricism is not wrong, they have to accept that it exactly equivalent to heliocentricism, and, by extension, that reference frames can be equivalent. But to argue that it is the only true reference frame they need to reject this relativism - and that's the goal. He claims this is a logical contradiction. I'm not so sure - I'm quite sure people will claim that the false reference frames are built on lies.

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#### Travis_King

I don't know about this experiment, but if you define your reference frame as the center of the earth, then it can be shown that everything rotates around it. This is a mathematically accurate description of the Solar system/universe, but it is not a physically accurate model.

Though, accurate isn't exactly the best word. It's more that it isn't the most practical, or the best choice for understanding how the solar system operates. You could work out all the natural laws of physics based on the movements of the planetary bodies given a non-rotating earth reference-frame, but it would be much tougher and would not provide you with an inuitive understanding of the actual motions of the planetary bodies.

#### Ryan_m_b

Staff Emeritus
If the person you are arguing with can't accept the simple and elegant answers listed in post 2 then no other evidence will persuade them.

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