# I guess I’m going to have to believe it now

Some people say we’re all standing on a giant rocky ball, which is spinning around — a ludicrously silly claim. But now I guess I have to accept it, because someone actually made a video recording showing it, by stabilizing the image to the stars. When you do that, you can actually see the earth moving.

You know what else is silly? The idea that I evolved from a rock. LaughingSquid is going to have to meet the creationist standard of evidence and show me a movie of that happening.

I know, this happened a long long time ago, which makes it more difficult, but I still have a VHS tape player, so I’ll even accept that antique medium.

Hey, I think my mother still has my grandfather’s old 8mm movie projector, so I’m willing to go even that far back. Checkmate, evilutionists.

1. rietpluim says

This is pretty cool.
It even gave me the sensation of falling off for a moment.

2. rietpluim says

P.S. My grandfather was an enthusiastic amateur filmmaker. We still have tons of 8 mm footage. Especially of cars driving by his front gate. He loved cars too, and there weren’t that many in his days.

3. Bill Buckner says

Fantastic.

I am going to use this video in an Honors class I teach on the history of physics to launch a discussion of a very deep, almost philosophical concept, Mach’s Principle: https://en.wikipedia.org/wiki/Mach%27s_principle.
To wit, this video shows the earth rotating with respect to the fixed stars. But if the stars were to vanish (as in gone, not just invisible)–would the earth still be rotating? And if so, with respect to what, exactly?

4. cvoinescu says

@Bill Buckner, #3
Yes, yes it would. With respect to its own axis. Mach’s principle applies to inertial frames of reference. A rotating frame of reference is not inertial, and the characteristics of its rotation (axis position, frequency) can be determined by observation wholly within the rotating frame.

5. marko says

I offered this very video up to a flat earther I made the mistake of debating with a while back. Unsurprisingly it left him entirely unconvinced, it takes heroic levels of cognitive dissonance and frightening amounts of paranoia to genuinely argue that the earth is flat. It was fun arguing with them for a bit, but I had to give up for the good of my health.

I do love that video, such a wonderful perspective.

6. carlie says

A swiftly tilting planet, indeed.

7. slithey tove (twas brillig (stevem)) says

re 5:
I can imagine their argument. Take a coin and spin it. It still flat, but the stars still rotate around it. Gotcha, Erth is phlat.QED
[or so I imagine, maybe they got something better IDK]

8. Matt says

That’s Kerbal Space Program music! Makes me want to build a rocket.

9. marko says

@7
Not quite, the earth is flat and stationary, the stars are points of light on an “astral plate” which rotates overhead. The explanation for the video is actually pretty simple (if you accept the astral plate thing), it’s just as PZ says “by stabilizing the image to the stars”, in all reasonableness it would work both ways.

The stars being visible on the horizon and overhead, and different stars being visible from different hemispheres questions are where it gets really fun, “it’s all done with mirrors”, I swear I’m not making it up!

10. Bill Buckner says

cvoinescu #4,
It is more subtle. A person on the earth can detect a centrifugal force and say– ahh, I’m rotating. And if you are rotating, you generally say that you are rotating with respect to something. What is that something? Is it rotation with respect to something absolute, and what then is this absolute? Is there an absolute inertial system? Or is it something relative, say a local inertial system, and if so does that local inertial system (and inertia itself) owe its existence to the large scale matter distribution of the universe? And hence the question of what happens if the stars (and dark matter) vanish.

11. cvoinescu says

@Bill Buckner, #11
You are rotating with respect to any and all inertial frames of reference. Together, the inertial frames of reference are the absolutely non-rotating thing with respect to which you’re rotating. There doesn’t need to be an absolute inertial system — any will do, and your rotation with respect to any of them will be the same.

I understand where you’re coming from — but only if this was translation, not rotation. Then there may or may not be an absolute, stationary inertial frame of reference, but even if there was, Mach’s principle says it would be indistinguishable from any other inertial frame of reference. (That makes its existence non-falsifiable — and as we know, to some, non-falsifiability makes discussion about its existence pointless, but, to others, it makes it interesting and profound.)

But rotation is different from translation, because we have an obvious, absolute reference for it: any inertial frame of reference. I’m pretty sure those would exist even if all the rest of the Universe vanished.

12. cvoinescu says

I should add that, in my understanding of general relativity, an inertial frame of reference doesn’t actually exist, since what is locally inertial is no longer so some distance away, given that space-time isn’t perfectly flat everywhere (all that pesky matter and energy curve it every which way). I’m pretty sure that there is still absolute non-rotation, relative to which things rotate.

13. Dauphni says

@Bill Buckner #3,
If all the stars were to vanish Foucault’s pendulum would still work just fine, thereby showing the Earth rotates.
And of course the Earth is notably is not a sphere but an oblate spheroid, which while maybe not conclusive is good evidence that the Earth rotates.

14. Ed Seedhouse says

@Bill Buckner #3
“But if the stars were to vanish (as in gone, not just invisible)–would the earth still be rotating? And if so, with respect to what, exactly?”

Well, if the stars disappeared meaning that we receive no electromagnetic radiation from any of them then our local star would disappear and the Earth’s temperature would be so close to absolute zero that there would be no philosophers about to argue the question.

A better question would perhaps be “does the universe as a whole rotate”? But the answer cannot be either yes or no because we can have no evidence one way or the other since by definition there is nothing “outside” of it. With respect to what can it be said either to rotate or not rotate?

That was, I think, Mach’s point in the first place. Something can only be observed to relate in relation to some other thing, and if there is no other thing to rotate relative to the very concept of “rotation” is meaningless. Not true, not false, just meaningless.

15. consciousness razor says

Newton discussed this with his rotating spheres and the bucket argument. Under rotation, objects are deformed, there’s stress or tension or what have you. You’d need to do some physics to find out exactly what happens to the objects, not just pick an arbitrary frame and proclaim it to be rotating or non-rotating. And you are going to see those effects, no matter what frame you may or may not have picked.

Similar to Bell’s spaceship, where the string breaks. Changing reference frames doesn’t give you things like that — there’s an actual physical effect that needs an explanation.