I was trying to think through the consequences of Einstein's observation that a freely falling body does not experience its own weight. And, as freely falling (or "inertial") bodies will always move like this unless acted on by an external force, then the obvious question presented itself, do we ever feel the effect of gravity, or is what we commonly refer to as the force of gravity always really just an opposing force?
For instance, if you were to fall through the event horizon of a black hole then the conventional wisdom is that you wouldn't notice anything untoward in the process whatsoever. It would only be if you tried to get away from the horizon, in a rocket, for example, that the extreme curvature of spacetime, that the enormous effect of gravity, would become noticeable. But then feeling this would be due to your acceleration, and not to gravity. As such, then, if you don't feel gravity acting upon you even whilst you're in one of the strongest gravitational fields in the entire universe, then I wondered "Do you ever feel it?
There was a similar question asked here about whether or not we feel gravity well over a decade ago. But all the responses simply went along the lines of "Drop a hammer on your toe, and you'll feel gravity!" which, quite aside from being unnecessarily juvenile, is also quite clearly wrong! If you let go of a hammer here close to the surface of the Earth, then, for all intents and purposes, the hammer doesn't move anywhere in space whatsoever. Rather, it is the surface of the Earth that moves, rising at 9.8 m/s² with your toe stuck firmly to it, that comes up to hit the hammer! If you "drop" a hammer on your toe, therefore, you are experiencing acceleration, which is an absolute quantity, in conjunction with the electromagnetic force - as your toe comes into contact with the hammer - as opposed to feeling the effect of gravity pulling the hammer down onto your toe.
All of this seems relatively (boom, boom) straightforward, but there's a caveat. Because there is still a gravitational effect, though small, that draws the hammer down towards the centre of the Earth's mass (I believe that, sans acceleration, it would take around three hours before an object came to "rest" on the ground). And so, bearing this in mind, then, although 99.99% (and, yes, I just made that figure entirely up) of the impact of toe against hammer is due to the accelerated toe, what is the correct way to think about the gravitational effect here? If not for the acceleration, would both yourself and the hammer not be inertial? And so always maintain a spatial separation until acted on by a force? Or are two particles that go bump in the night actually experiencing gravity?
In short, can you ever truly feel gravity, or can you only ever experience opposing forces?
NB¹ General relativity is a precocious, demanding, and not to mention deceptive, mistress. Just when you think you understand her she'll suddenly smack you in the face again, and usually while screaming "Idiot!" at the top of her lungs. So, bearing this in mind, then, I've tried to be careful in how I've described her (take it from me, you don't want to say something like "Your gravity looks big in those jeans". That sort of thing never ends well! But, knowing me, I've still probably screwed up the description somehow, and so, if I have, then all I can say is, "Sorry, please don't hit me again!".
NB² I am an "armchair physicist", a complete layperson, and I hold no capacity whatsoever for mathematics wherein the number of summed digits exceeds the number of digits on my hands (and even then it can be problematic!), so any answers with equations in them, while doubtless proving worthwhile to others here, will be essentially meaningless to me. And, yes, I'm well aware that physics without math is an essentially meaningless concept in and of itself, but I'm an old dog, and well past learning new tricks. I came to physics late, too late, but I still derive an enormous amount of pleasure from understanding, as best I can, how the world works on a strictly intuitive level.
NB³ Oh, and just in case there's anybody out there who still has the "jump out of a plane and you'll feel gravity" mentality, I can assure you that you won't. There are a myriad of thought experiments one can conduct by which this can be fairly easily demonstrated, but, for brevity's sake, here is an actual experiment that anyone can do in order to prove it for themselves that, should you ever decide to jump out of a plane, you won't move anywhere: you have a phone. Your phone has an accelerometer built into it. Download an accelerometer app from your respective app store. Take a reading with the phone at "rest" on a table. Now push your phone off the table (such that it "falls" onto a cushion), and see what the lowest reading was. At "rest" on the table your phone will show that it was accelerating at around 9.8 m/s², and the reading as it "fell" will show 0.0 m/s. And it will show this because, when your phone appeared to be falling, it wasn't. It wasn't being accelerated, it wasn't actually moving, and it didn't, in fact, move anywhere in space at all! It's a whacky world, ain't it?
Thanks to anyone that read this far. I apologise for the "book" - writing more than is strictly necessary is a bad habit of mine. And finally, to anyone who can provide an answer to my question (one that my limited brain might be able to apprehend), then I thank you most gratefully in advance. My intuition is that we can't ever feel the effect of gravity, but then our human intuitions are almost always wrong, so... little help, please?
Avag'day, all!
♪♫︎ `𓅷´´ ♪♫︎♪
