I think a famous physicist claimed that if you stood still and the entire universe spun around you, you would get dizzy. Is that true? I don’t see how. I will already modify it to: “if you were floating in interstellar space and the entire universe spun around you…”, for obvious reasons.
Are you talking about[Mach’s Principle](Mach’s principle)?
TriPolar’s link is broken; here’s the wikipedia article: Mach's principle - Wikipedia
I’ll also note a potential point of confusion in the ensuing discussion – if you were floating in space and things were spinning around you fast enough for you to perceive the motion, you may indeed “get dizzy” due to the disconnect between your visual perception and your vestibular system. But that has nothing to do with Mach’s principle and is not, I believe, what the OP was asking about.
Thanks for fixing that. It is a weird thing to think about. Even though I don’t really understand it but it does make some kind of sense. How would I be able to tell the difference between the stars whirling around in the sky while I stand still, or me spinning around while the stars stand still? I don’t know but I can understand that there may be no difference at all, and I’d feel the centrifugal force either way. Or else I don’t get it at all.
Dizziness is about a lot more than just physical motion. The brain reacts to what the eyes show as well. It’s why, if you stand in front of a big TV screen, and it shows a freight train at 100 miles per hour charging headlong towards you, you may still feel the instinct to duck out of its way, even if you intellectually know that the TV screen is just a screen.
So if you are standing still but everything around you suddenly starts spinning fast, your eyes and brain are conditioned into reacting to that the same way as if YOU were spinning fast.
Assume your eyes are closed.
What makes you dizzy is the fluid in your inner ear canals. If the fluid is not sloshing around, you won’t feel dizzy, no matter what is going on around you. If you are in an inertial frame (i.e., not accelerating, which also means no rotation) then there will be no fluid motion and no dizziness.
If you open your eyes you will get hella disoriented but that’s different.
It’s not really about getting dizzy. When you spin around fast you should feel the centrifugal force on your arms if you put them out to the side. If I understand it right, you would feel the same if you were standing still and the stars were whirling around you.
Ever walk through a spinning tunnel at a haunted attraction or amusement park?
(bolding mine)
Unless the OP asks a mod to change the OP we’re going to see one explanation after another about why people get dizzy.
The brain relies on multiple feedback systems. The fact that the fluid in the inner ears is not moving when the eyes are seeing motion causes problems. It is little different from the fluid moving and the visual field being fixed. It’s this difference in data coming in that causes the problem. That one of the data streams is “correct” in some sense is not relevant.
The Spinning Tunnel effect is a really great example of this. You can see people lean to one side and almost topple over.
Rewording:
You are floating through interstellar space and you happen to be blind. Everything in the universe starts spinning around you. Do you get dizzy? Does the fluid in your inner ear start moving wacky?
Inner ear fluid moving is A cause of dizziness, but not THE cause. There are many things that can cause dizziness.
You will not feel any centrifugal force if you are not rotating but everything else is spinning around you. There is no centrifugal force in an inertial frame.
How could everything in the universe start spinning around you in any way other than by just spinning you? To leave you “stationary” but spin everything around you would imply accelerating the mass of the universe by ridiculous amounts wouldn’t it?
In addition to the article on Mach’s Principle, there’s an extensive article on the Bucket Argument that lays out the (non-trivial) problem.
It’s a tricky problem that I don’t think has really been resolved - about whether absolute rotation means anything, or where inertia comes from. A brief description here:
http://nautil.us/blog/-this-is-why-understanding-space-is-so-hard
But that’s the issue: is the case of the entire universe rotating around you distinguishable from the case where you are rotating? If the entire universe were rotating around non-rotating you, would you be in an inertial frame? Is there such a thing as absolute rotation? Where does inertia come from?
From the perceptual point of view, what you describe is called an optokinetic stimulation.
Given the proper rotation parameters, you will feel as if you are spinning and the universe around you is stable:
- The rotation must be a constant-velocity rotation. This is because the semicircular canals in the inner ear detect angular acceleration, and therefore change in the rate of rotation will cause sensory conflict (and break the illusion that you are spinning). Likewise, the illusion often needs a few seconds to build up.
- The rotation must be slow enough, I’d say below 90 deg/s. This is because when you are rotating, the semicircular canals help stabilize your gaze in space, which allows you to see sharp. During an optokinetic rotation, the visual system can also drive a feedback loop where the eye follow the visual surrounds, but that loop saturates easily. If you spin the universe too fast, eyes will stop following the visual surround, and everything will look blurry.
- Even with the proper conditions, humans tend to experience a bistable perception, with alternating periods where they feel spinning and when they feel that the surrounds spin.
There are some more cool things that can happen:
- If you were to move your arm away from your body, you brain (who thinks that you are spinning) will anticipate coriolis forces. These forces won’t happen, and you will “feel” the missing force. It will feel as if some force was pushing your arm to the side (in the direction opposite to where the coriolis force would have been).
- There is a somewhat similar effect that happens if you spin your head in a plane different from the plane of optokinetic stimulation. Combinations of rotations have activate semicircular canals in a slightly complex manner (this is incorrectly called coriolis activation of the canals; a more correct name is vestibular cross-coupling; it is used in the ‘pitch while rotating’ motion to train people against motion sickness). Your brain will actually anticipate it to happen (but it won’t happen since you are not really rotating). That feels disorienting, too!
This seems to be a restatement of Newton’s rotating bucket and the issues raised by Mach. Perhaps OP could clarify, but as I understand it he is asking about the fundamental physical principles: is rotation defined against some absolute non-rotating frame, would a non-rotating body experience centrifugal force if the universe were rotating around it.
Assuming that OP is not asking about the specific biophysics of how we get dizzy, that aspect is a red herring, and it’s better to frame the question in the traditional form of water in a rotating bucket.
Thank you for this.