Short of collision, can gravity itself kill you?

Yes gravity can kill you because as you approach something super dense like a black hole, the gravity will change with the square of the distance which means that eventually the gravity at your feet would become significantly larger than at your head. This gravitational gradient is referred to as tidal forces and is the same effect that keeps the same side of the moon facing the earth.

This would tear you up and eventually disassemble the matter that makes you. Although it sounds dumb, scientists actually call this spaghettification as the CuriousOne has already mentioned.

It is questionable whether other effects like gravitational blue shift would not kill you prior to the spaghettification of your body.

A uniform gravitational field (which is actually only hypothetical) would have no effect comparable to spaghettification as it merely results in constant acceleration of your body.

It's fair to say that the "spaghettification" problem occurs where there's a strong enough gravitational gradient across a typical body-distance - but your question seems to ask about cases where the gravity is great - extreme, but uniform (at least in terms of human proportions/distances).

Einstein’s principle of equivalence states that, as long as there's no reference externally, any gravitational field feels much like another. So if I'm in freefall into Jupiter, or the Sun, or Phobos, or wherever, I will still feel weightless, the bowl of petunias free-falling with me will also feel and appear weightless next to me. It's only when/if I look outside of the frame of reference that I might notice any difference. For example, if I were in some high gravitational field, the rest of the universe might appear to be running very quickly, turning blue, and looking very bright indeed.

If the field were strong enough, and the outside universe bright enough (we're talking about starlight here, so it depends on where in the universe you might be, and how bright the stars are nearby - but in cases where a strong field might exist, such as near a super-massive black hole, you might find yourself at the centre of a galaxy where, presumably, you might expect the starlight to be significantly brighter than here on Earth) The "blueshifting" of low-frequency radio-wave type photons might act as microwaves, initially heating up the body fluids, visible light would shift towards ultraviolet, perhaps causing sunburn, and as we go up the frequency spectrum, xrays and gamma rays would effectively be delivering strong doses of dangerous and harmful radiation. If this were bright and strong enough, it ought to break down the proteins and structures within your cells and potentially, reduce you to a steaming pool of jelly.

So, my advice is, wear sunscreen!

While a sufficient difference in gravity over your body will kill you, gravity itself will not kill you.

It's not really clear if you're asking about hypothetical, relatively uniform gravity fields, or black holes. Since the other answers tackle the latter I'll go for the former.

Answering what I interpret to be your question, given the following ideal assumptions:

  • You are in an extremely strong, homogeneous gravitational field (same forces acting on your entire body).
  • The field is infinite in size and there is no "ground" or other objects to collide with.
  • None of the other conditions present can kill you (e.g. you are magically able to survive with no atmosphere).

You will experience only an ongoing acceleration due to the effects of this gravitational field.

Density and mass do not affect gravitational acceleration. Even though your body is of non-uniform density, it does not matter, so all parts of your body will accelerate uniformly in this hypothetical homogeneous gravitational field.

You will simply move faster and faster, approaching the speed of light, but no harm will come to you. You will feel "weightless" and you will observe any stationary objects moving past you faster and faster.

You don't need the field to be homogeneous to survive either. It only needs to be "homogeneous enough" so that the tidal forces don't exceed your body's structural strength.

Now if you throw yourself in a black hole, that's another matter entirely. As already described in other answers, the difference in gravity over your body will cause the parts of your body to accelerate at different rates, and these forces tear you apart when the structure of your body can no longer withstand the forces. The cause of death here is the force that the parts of your body exert on each other due to their relative motions, as some parts begin moving faster than others.

Of course, these conditions don't really exist, but it's hypothetical, like your massless ropes and frictionless pulleys.