I don't think that is quite right.
Yes, there could be some problems with it. First, the word "observation" implies some consciousness, so probably it should be rather called "interaction", "interaction of information", or "infointeraction". But it doesn't exist, word "existence" implies some particular state, but it doesn't have one, and its atoms can be in a state "scattered all round the universe". And assuming the contrary has some interesting consequences for human immortality.
In the end, it's a discussion about word definitions we use.
As for Schrödinger, let's marry quantum with relativity for a while. Let's call the spacetime outside of the
light cone Schrödinger's Spacetime, since we can't exchange any information with it, and if there's a cat, it is a Schrödinger's cat. What's more, let's assume that
v <= c (our velocity can't be greater than the speed of light). Let's multiply it by time:
v*t <= c*t which means that the distance we can travel in t time cannot be greater than a distance light ray can travel in this t time. For now it's rather obvious.
But that's not entirely true, we've silently assumed that t >= 0. If t<0 it means we travel back in time, and we can equivalently write: -t, where t>0. Let's multiply it:
-t*v<=-t*c, so after some mathematical magic we get
t*c <= t*v. This time
it means, that if we travel back in time, distance of our travel must be greater than that of a light ray, so we fall out of our light cone into Schrödinger's spacetime. It means we cannot kill our grandfather, even if we could shoot a bullet with the speed of light, it would need t+epsilon time to reach this particular spacetime, i.e. it will reach *after* our departure. So in this way Schrödinger's cat saves our grandfather (and us of course) and we don't have to deal with the Grandfather's paradox.
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