In zero-g there is no such thing as "landing on your feet" because there is no such thing as "landing". There is no "down" direction so of course cats can't detect something that doesn't exist.
Whiskers. Every cat is perfectly aware of the rapidly accelerating wind rushing past its head. Then they have ears to hear that wind. Lastly they have eyes and some experience with life on solid ground. They see it coming and understand what that means... Unlike sperm whales.
If you have a cat in a cylinder of air in space, and push it toward one end of the cylinder, I think it would get those signals since the cat is being pushed through the air.
Having done "zero-g" in aircraft many times, you do feel it. Your blood shifts. Your spine decompresses. Your head gets lighter. You very much know that you are falling.
A lot of confusion here probably comes from the fact that g-force is not the same as acceleration. It's apparent acceleration. So 0g in an aircraft is entirely possible. So is 0 acceleration but that's not 0 g, that's 1 g.
the cat experiences "zero-g" as it accelerates towards terminal velocity
I think you meant the cat experiences 'zero-g' AFTER it's done accelerating and has reached terminal velocity.
I'm guessing in most cat falling situations the cat does not reach terminal velocity, so it is accelerating the whole time and can adjust based on the direction of acceleration.
No. Terminal velocity is one-g, the same as sitting in a chair. A skydiver at terminal velocity feels exactly as much force/acceleration from the wind as they would feel force from lying down on the ground.
I'm sure that it keeps track of which direction is up with the same inner ear mechanism that we use for our balance. Given that it starts properly oriented thanks to gravity, and doesn't spend long falling, this gives it a good idea which direction is up when it lands.
Spend long enough out of gravity, and it will get confused. As do we.
Could also be the sensation of air rushing past [1]. Curious to test the competing hypotheses--dead reckoning from initial alignment versus air movement--in a wind tunnel.
That’s what I thought too. The cat loses its plumb vector if subject to zero g for too long. Under normal circumstances, the cat quickly reorients along the previous plumb vector.
> The problem with that theory is that while a cat is falling it is in zero G.
Ah, yes, I see your point. Air resistance would eventually kick in and provide positive G, but not in a short enough fall. And cats are heavy enough that "a short enough fall" probably includes most falls in which they are observed to land on their feet.
A cat's whiskers can detect very minute air movements. Even without whiskers, a human face can feel slight puffs of air at tiny speeds, speeds that falling objects hit within inches. Wind alone should give the cat enough directional information within milliseconds. Whether it can adjust its body position in time is a different issue. It certainly knows in which direction it is falling practically instantly.
Cats also have memory. They remember in which direction gravity was pulling them before the fall. Absent every other sensation that memory should be enough to get the process going even absent new sensations.
About the memory part, it can be interesting to see in a perfectly black spherical chamber to first lose sensation of any direction, then to try the experiment to rule out the possible effect of memory.
Yet, I hope no one tries this as it might perhaps be traumatic to cats.
While falling, the cat is in an inertial reference frame, so it is not accelerating. The ground is actually accelerating upward at 9.8 m/s2, counteracting the flow of spacetime.
There's a difference between accelerating compared to a coordinate system, and accelerating compared to an inertial rest frame. If you set a fixed coordinate system relative to the ground, then yes, the cat is accelerating towards the ground.
Consider this: if you hold an accelerometer while stationary on the ground, it will read 1g (accelerating). If you read an accelerometer while in free-fall, it will read 0g (ignoring wind resistance). In the first scenario, you are accelerating compared to your rest frame, even if you are standing still.
This is not an arbitrary distinction either. The 1g of acceleration while stationary on the ground produces measurable relativistic effects.
An accelerometer doesn't measure what you think. It measures the difference between the acceleration of the casing and the internals, for an example. It is designed to show 0 in free-fall. Yet, it still is under the force of 1G towards the center of the Earth.
There's more nuance to it than that, so let me try to clarify again. Like you said, the accelerometer shows the difference between the casing's reference frame and the internal's reference frame. The internals ideally maintain an inertial reference frame. It's only "designed" to show 0g in free-fall because the difference between the reference frames of the casing and internals _is_ 0 when you are falling. Because, again, when you are falling, you are in an inertial reference frame - you are not accelerating against the flow of spacetime.
The only time the accelerometer reads something other than 0 is when something pushes it away from an inertial reference frame. This is true when you're on the ground: spacetime is curved, and "flows" towards the center of the Earth. The ground pushes you against the flow of spacetime, and the difference between these two frames of reference is 1g. Note that this 1g is not "caused" by gravity, it's caused by the electromagnetic force. Forces push matter away from an inertial reference frame. Gravity is different. It decides where an inertial reference frame goes by curving spacetime - it is not a force.
Hypothetically, if you were are the center of the Earth, the accelerometer would read 0g. There would be nothing pushing you in any particular direction - you would be in an inertial reference frame (ignoring the minor detail of being crushed by all of the Earth's mass).
Again, I'm trying to show the subtle difference between accelerating compared to a fixed coordinate system, and accelerating compared to an inertial reference frame. The fixed coordinate system does not take into account the curvature of spacetime. If it did, the coordinates would be "accelerating" towards the center of the Earth at 1g - congratulations, you've defined an inertial reference frame.
I hope that makes sense. It blew my mind when this idea clicked: that space and time are not two distinct things, they are two parts of the same thing.
Well, yes, but I never disputed any of that. I wrote, "A cat is not a rigid body and is absolutely accelerating towards Earth, experiencing the physical effects of gravity." Are you saying that is wrong?
Good point, although as long as they are not in contact with any surfaces it seems pretty safe... Until they figure out how to propel themselves, which would be gross.
In The Expanse books they made a point of showing that the inners (earth / mars) had difficulty with zero-g combat because they would try to lean back into corners and inadvertently push themselves out into the open.
That's certainly the intuition most people would have about this, but it's still interesting to see it borne out when in principle there could have been other, surprising signals that cats respond to in order to right themselves.
Acceleration is a vector. A vector is magnitude and direction. "Down" is a direction. If there's no acceleration, there's no "down". That there is no acceleration in "zero g" is a critical difference between "falling" and "zero g" in this context. Therefore, they aren't the same.
True, but which kind of acceleration are we talking about?
A cat in the "zero g" in the experiment described in the video has no coordinate acceleration relative to the Earth. Whereas a cat falling off a ledge to the floor does have coordinate acceleration relative to the Earth.
But both cats have zero proper acceleration--they are both weightless. (Air resistance will become significant at some point during a fall from a height to the floor, but cats are heavy enough that I don't think that would be significant in most falls where cats are observed to land on their feet.) And "zero g" means zero proper acceleration, not zero coordinate acceleration. So the GP is correct and my original comment was in error: cats in both situations are in "zero g" so that can't be what is causing the different behavior in the two situations.
I've never thought critically about this - but in free-fall on earth, you are falling through the air which could be used to measure the direction of the fall.
I think most people would consider “falling” to be going “down” a gravity well. Stable orbits around a gravity well, or at sufficient distance to not be influenced by it, are not what most would consider to be “falling.”
In the sense that matters for this discussion, zero g is the same as falling--both are weightless conditions. So the GP is correct and my original comment was in error; "zero g" can't be what is making the difference.
I think more precisely, the traditional definition of an orbit (stable or not) is that it's influenced by gravity. You could be in a situation where the influence of gravity was negligible (say, far beyond any galaxy) but it wouldn't be considered an orbit at that point.
I guess certain multi-body situations like Lagrange points might make it debatable about which "direction" you're falling though.
I agree with mrexroad. Falling implies downward velocity. Free-fall is a different term that implies downward acceleration. For example, a ballistic projectile fired up that then falls back down first climbs, then falls, but it is in free-fall the whole time.
> Falling implies downward velocity. Free-fall is a different term that implies downward acceleration.
The GGP didn't say zero-g "is" falling. They said it's "the same as" falling. Which, for purposes of this discussion, it is, for the reason I gave--the key common property is being weightless, i.e., free falling.
Note, btw, that "free-fall" does not necessarily imply "downward acceleration". It just means "weightless". You could be weightless, in free fall, far out in deep space well away from all gravitating bodies, so that there is no well-defined notion of "downward acceleration" in your vicinity.
Regarding your second point, I think everywhere in the universe has some direction of the gravity field, however weak it is, and that would be the downward direction. But yea in some ideal place with exactly zero gravity, there's that special case.
My plan is to go to Mars with the first domestic pet cat; it implies a level of civilization/comfort/safety (to be able to have pets) which is consistent with what I'd want myself. Maybe 10k people? 50k? Hopefully I live that long.
Every major sea voyage of the past had a cat or two, they were necessary to keep rats from eating all the food supplies.
Apparently the cat on board the expedition that discovered New Zealand immediately upon reaching land jumped out and grabbed a small flightless bird (then a brand new species discovery) and dragged it on board to eat.
Ocean ships have rats so they would tend to have cats even if people didn't encourage them.
With the COTS technology of cat diapers I think they could have a pet cat on the ISS but they don't want the risk that it goes wrong and they'd have to put it down.
There's also the smell, by all accounts the ISS already smells a little bad from decades of BO and grime, I would not want to add the smell of cat shit to that.
The decommission date gets pushed back any time it gets close I doubt it will actually be considered until there's major structural issues. The time always seems to be "when we have a commercial alternative" which is economically a pretty long ways off from the looks of it.
I doubt cats have a substantially harder time surviving g-forces than humans. Smaller animal should be less affected; plus, commercial manned launch g-forces are going to be pretty low peak anyway. Maybe 4G?
Cats can be trained to sit on and use a human toilet seat. A space toilet with a vacuum would be more challenging but I bet a dedicated animal behaviorist with enough time and training could get a cat used to using a space toilet.
It may just be easier to design a zero G litter box. A screen bottom with a coarse granular material and sufficient airflow through the bed could work. No idea how a cat would dig in zero G though.
Sturdy screening to give claws a grip would probably serve as the equivalent of human handholds just generally. I don't know how comfortable or feasible walking on it would be, but I bet a cat could learn pretty quick to catch on to it and then push off along a desired vector, and they're already better at gyroscopic pointing than we are.
Pixel walks through walls because nobody explained that it can't be done, so I imagine the same would apply for breathing in and staying pressurized in a vacuum
> Don't know what you'd do for the litter box though.
dear god... the image of a regular litter box in zero G made me wince. I had a cat years ago who was an excavator and make a big mess whenever she went on archeological digs.
Another thought, cats typically bolt from the litter box after pooping (one guy I have does an amazing 90 degree wall kick-walk ninja move to run downstairs.) Not happening in 0G :-)
I thought about picking up the turds with gloves, wondered what I'd do about the urine, or what I'd do if the stools were loose and then I thought "are cat diapers a thing?" and it is available COTS
Who says cats don't have grabbing appendages? Ever tried to deal with a frightened cat who wanted to put you between them and whatever they were scared of? Like if Velcro were made out of fish hooks - they can grab like a hot damn, and in my experience "damn" is the very least of what you'll say when they do.
More to the point, cats climb trees with their claws, so making ISS interior surfaces amenable to feline use is just a matter of finding a material that's enough like bark for them to get a grab, and durable enough to hold up under long use.
I was thinking the same thing. They're still rotating the way they normally would. Toward the end of the video the orange cat floats "up" from the floor toward the ceiling and turns it self around to "land" on the ceiling feet first.
Yeah, those guys kept kicking or pushing cats preventing them to orient themselves. Cats were surprised by the lack of gravity, but they were not given a chance to adapt to new circumstances.
These parabolic flights give you ~25 seconds of a close to zero-g environment, but bookended by some pretty uncomfortable ~+-2g before and after periods. It would be interesting to see the cats in a more stable and extended zero-g environment to see how they adapt over time.
When a cat is in free fall, that is weightlessness. At least initially, until air resistance starts limiting the velocity.
In zero-g, you do not directly sense in which way gravity is pointing.
Probably, under the conventional free fall situation, the cat is relying on visual clues, and the sensation of air moving through its fur, to establish which way it is falling, as the basis for the righting reflex: which way to aim the paws. Those clues are absent in the simulated zero-g environment, which feels like free fall, but the cat doesn't see any relative movement to anything, or feel any air movement.
That should be pretty easy to test. Anyone know if blind cats land on their feet? If blind cats are in general too geriatric to test on, what about a blind fold, and dropping your cat upside-down on a bed?
Could you accomplish the same thing in a ground based lab with a fan blowing air up at ~80 degrees? If airflow is used for orientation, then the test subject should orient to be parallel to the direction of airflow as it is falling.
All for Science, of course.
(The 80 degrees thing is there so they don’t hurt themselves when they reach the ground - hopefully being only 10 degrees off vertical will be recoverable).
It wouldn’t be a super ethical test.. but I wonder if a cat would adapt and start doing some really crazy ninja moves all over the place, if you left him in zero-g for a few years.
You misunderstand cat adaptation !!! These little bastards would learn to swim lazily before spending any effort on ninja moves :D Have you seen a well-fed pampered cat, the thing will meow for his food before even turning his head towards its human slave.
Those auto righting reflexes are just there to ensure their eternal survival when presented to (rarer and rarer) danger.
They're Gods making us do their bidding while they pretend we're the masters :D
Unethical? Have you seen the inside of the ISS? It's cat heaven with all the cables and stuff hanging around, and nothing is too high to jump on when you're almost weightless :)
But a cat free-falling from a height is also weightless, and yet they manage to right themselves using perceptual cues. The point of the experiment is to see how the behavior changes when the sensation of weightlessness is presented for an extended period of time, without the "falling" motion (relative to the perceived local environment) that normally accompanies it.
The cat's system has memory. The transition into free-fall from a state where it was previously experiencing ground reaction force provides a cue for the self-righting reflex on the direction of "up/down". Apparently even blind cats can self-right based on their vestibular system.
It might have been interesting to re-run the test with a more obvious "horizon" and see if the cats react to that. Then if the cat still doesn't right itself, it seems like it is using acceleration rather than vision to determine which way is down.
Before a cat (or any object) experiences free fall, they experience acceleration so they know which way gravity is pulling them. Surely, a cat can remember what happened to it in the last few seconds and instinctually put its feet in that direction?
I think that's the point, they do not experience acceleration in zero g, which is the point of testing visual/aerial cues, which DO remain in free fall (electric fans, horizons).
I'm fairly sure you just read this backwards, thought I'd explain better.
This is interesting because, it provides information on how the cat brain might function - if they have accelerometers embedded in their brains, that is quite interesting, but somewhat unlikely (birds have magnetic sensors, not impossible or unprecedented), if, perhaps more likely, they have incredibly sensitive hearing or sensation on their fur, which they interpret as acceleration, that is also interesting, in a different way.
Do we know it's visual? If you drop a cat in darkness (onto a pillow of course), will it right itself? What if you put it in an elevator that accelerated downwards at 1G so the cat fell to the ceiling? How does it know which way is down? Is it the horizon, or the bright sky, or does the cat remember the scene before it was dropped? Or is it the air rushing by?
Dear scientists, for the love of all that is good, don't repeat this test.
Cats aren't ever going to forgive you for engineering a situation where they are seen to land in an ungraceful way, and there's a tiny chance that they will make us all pay when they evolve opposable thumbs.
Cats can't be bothered to evolve opposable thumbs. They have human staff to take care of anything that requires an opposable thumb, why would they bother doing it themselves?
Cats are crafty enough to both survive and plan for a post-human landscape, such as climate change, World War III, or supply chain issues driving up cat food prices.
As suggested by some I guess cats would (eventually) learn to move in zero-g. I also guess that these cats didn't get enough time to "learn" what to expect and their disorientation kept them from turning to land on the oncoming wall. Their eyes tells them that the "human" is sittning on the floor and for some reason they're floating towards the ceiling.
It's not like cats evolved in a place where the direction of up changed that often.
I wonder if "zero-g cats" would learn to use their claws to hold on to "walls" (provided suitable surfaces were provided).
That's not what a dropkick is. In a similar way to someone else pushed a cat, the man used his foot to move the cat away from the floor, but because of the zero-g, it caused the cat to move to the ceiling. Hardly unethical.
Considering cats fall feet first and buttered toast butter side down you can power your spaceship by taping buttered toast to your cat's back and attaching the cat toast contraption to the rotor of a generator
the cat righting maneuver is a zero-angular momentum maneuver, so if the cat has a slight amount of spin, it is not possible for the cat to correct it. That may be what happens in the video
Off topic: Kettlebells might lose their "heavy" in micro-gravity[1], but they don't lose their "massy". I first read the term "massy" in some sci-fi book, by Heinlein, I believe.
It takes more effort to overcome the inertia of an object with a lot of mass than it does to overcome the inertia of an object with less mass. So, you can still use massy objects to work out in micro-gravity! Or so I've been led to believe by convincing fiction. :)
1: I've also been led to believe that micro-gravity is a better term than zero-g for the conditions experienced during free fall.
