Want to know gravity? Lay flat on your back.

At some point in the distant past, I realized the truth about gravity. Because gravity isn’t a force. Gravity is a bending in space-time.

Here’s how I did it. It may not work for you the way it worked for me. But it worked for me just fine. Perfectly, in fact.

bend in space-time

No pull. Just acceleration. That’s pretty cool. (source)


I simply laid on my back. Yes, there were trees around. And yes, it was a pristine location surrounded by natural beauty. But none of that really mattered. What mattered was what I experienced as I lay on my back. And it would be the same no matter where I laid. I could have been in bed, laying on my back on whatever kind of mattress you might want to spend your money on. In my case, it was grass. Just grass. Just a flat patch of grass.

As I lay on my back, I realized that it was exactly the same feeling as if I were laying on my back in one of those spinning carnival rides, where the passengers begin standing against a padded wall, and then slowly, as the whole spinning contraption begins to rotate, you are pressed against the padded wall behind you. Until you realize that the padded wall behind you is really the padded bed beneath you. Because centrifugal force is pushing against you, turning the wall into the floor.

But there’s more. Just laying on the ground, on the grassy ground, I felt that I was accelerating upward. This is exactly the way Einstein described gravity. Gravity is no different than acceleration. A constant acceleration gives you the sense of weight. A constant acceleration is gravity. You can lay on the ground and get the definite sense that you are accelerating upward. And there is no difference. In fact, the gravity that you experience in that way is exactly the same as the gravity you feel at all times, while you are awake, walking around on this massive planet we call Earth. You are within and about the bent space-time caused by the mass of the planet.

Cool, right? Try it. You’ll get it.


KJC dingbat-thumbnail


About Keith Croes

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Posted on February 27, 2016, in astronomy, Gravity, physics, Science, Writing and tagged , , , . Bookmark the permalink. 10 Comments.

  1. An interesting and germane physics demonstration. https://youtu.be/MTY1Kje0yLg


  2. Accelerating upward? Meaning, towards the sky? Like you feel like you could fall into the sky? …if not for gravity constantly curving that fall, pinning you down? Or are you talking about something even more nightmarish? 🙂


    • Here is something of what I mean:

      In the physics of general relativity, the equivalence principle is any of several related concepts dealing with the equivalence of gravitational and inertial mass, and to Albert Einstein’s observation that the gravitational “force” as experienced locally while standing on a massive body (such as the Earth) is actually the same as the pseudo-force experienced by an observer in a non-inertial (accelerated) frame of reference.

      In fact, I believe at 1 g, you are constantly accelerating in the space-time around the mass of the Earth.


      • Got it except why upwards?


        • As that’s the direction you’re facing when you’re laying on your back.


        • Maybe you got all the good gravity. I always experience that as accelerating downwards.


        • You’re facing toward the bend in space-time instead of facing away. And if the sun and moon were aligned directly to your back, you’d be fit to be tide.


        • Funny 🙂
          Bah, I’m just not getting it. Maybe it’s a matter of various aspects of different analogies appealing to different people?

          I always experience the space-time bending aspect of it in 3d, external and internal to both myself and the Earth. The bend isn’t like a bend in a sheet of metal or a trampoline because it’s 3d. We say that, and I can think “Great. Got it.” and pass a lie-detector test, but then I’m still imagining flat stuff with their flat-stuff-dynamics but vaguely 3-d-ified, which is probably good enough for a mind made of meat, but I know there’s much more waiting in the wings.

          For example, the trampoline’s fabric is shaped like me instead of flat, but it’s also very think, maybe infinitely thick. But how can it be shaped like anything if it’s infinitely thick? (Heat that I’m producing in a room is only me-shaped if it doesn’t fill up the entire room. If it does, then it’s not me-shaped; it’s room-shaped.) But a shape can be understood by the density of the fabric not being uniform to begin with. Also imagine the density changes over distance. And in the amount of change we see again out of the corner of the eye a fundamental truth or lie of our existence, so big that it’s impossible to see by looking straight at it. Impossible to describe with words and neural networks, but impossible to un-see …and that’s not even mentioning time.


        • Yes, the bend is all-dimensional, not like a trampoline at all. But it’s still a space-time bend in which your mass is totally immersed. Imagine the trampoline on every plane there is (infinite surrounding planes) around a large mass, like the Earth. The bend in space-time directs you toward the mass, as if you’re always falling toward it. Because, indeed, you are—an identical situation to what we think of as acceleration, or what feels like acceleration. The reason for my post was precisely because this feeling of laying on my back felt exactly like acceleration…1 g of acceleration headed upward, which happened to be the way I was looking. No drugs were involved. Just the realization that those two things were exactly the same…that gravity was acceleration in space-time. Easy-peasy.

          Actually, not easy at all. And yes, our senses are limited, even useless to experience what is really happening here. It’s a thought experiment, where most of Einstein’s insights derived.


      • Oh, I get it! Up is the direction you’re facing when you’re laying on your back. 🙂

        Liked by 1 person

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