If I clone two earths right when the first unicellular organisms formed, with everything down to the atom similar, will the two earths (or maybe just take them as universes composed of matter/energy) be the same? If not, why? What causes that difference? Is it randomness? If so, what causes this randomness?
Thank you, this is my first question.
Suppose there is no randomness, only causality. Then what causes the causality? The explanation for how the whole system works has to come from outside the system. That’s.still true if there is no randomness.
Uncertainty would prevent identical copies to begin with.
And even if you could do that, which you can’t, wave function collapse(s) would make them diverge almost instantly.
Also, if someone tried to do it within our universe, the distances between the two Earths and e.g. the nearest stars or galaxies would be different, so the gravitational force would introduce differences.
Just adding that this is true regardless of the interpretation of quantum mechanic.
In collapse models, each Earth’s wave function collapses separately, i.e. rolls different random numbers. In many-world models, we get a Cartesian product of “whatever happened to Earth1” and “whatever happened to Earth2″, and in most results, the states of the two Earths are different.
Chaos is a major factor. Small differences in initial conditions can grow to become large differences in final conditions.
If it’s only “down to the atom” similar, then there’s a lot of information not carried over into the other universe. The copy will diverge due to the different lower-level details even without considering annoying concepts such as those in quantum mechanics.
Quantum randomness is fundamentally random, unless you believe in hidden-variable theories, superdeterminism, or something something Bell’s theorem loopholes.
This is true for both shut-up-and-calculate QM and for MWI; the difference is whether the universe is random, or whether the “branch” that your subjective experience ends up on is random. In the latter MWI case, I think any observer looking at the two clones Earths would still see divergence, because an observer is unable to somehow probe the universal wavefunction and see the deterministic evolution of wavefunctions or whatever anyway.
There’s a separate question of whether you can “see” this randomness, and thus whether quantum randomness even matters. The answer is really yes. As one example, mutations can be caused by cosmic rays. Maybe an extremely fit genotype came to be because of a cosmic ray, that happened to come in the right direction due to the randomness from pion decay in the upper atmosphere. That would be a major macroscopic deviation that would happen over generations. There are probably many other such things.
Also, quantum theory forbids wavefunction clones, so the initial state of your two Earths would already be different (different different or different Everettian branches). This is my understanding of the no-cloning theorem, at least.
I have a very limited understanding of this subject, but this is my best attempt at constructing a coherent answer: it’s an open scientific/philosophical question.
Anything in scare-quotes (“Like this”) below is a word or concept that I only have rudimentary, incomplete, or mistaken understanding of- you have been forewarned.
Currently, our best understanding of the time evolution of the universe is given by the standard model of particle physics, which is quantum mechanical and uses the Schrodinger wave equation to predict the behavior of subatomic particles like electrons. The Schrodinger wave equation gives PROBABILISTIC answers, and you only get “waveform collapse” and “the application of the Born rule” when you actually interact with the system (“make an observation” or “cause decoherence”).
Now, there are some interpretations of this framework that basically say: that’s it. The bedrock of reality involves random wavefunction collapse and you interpret that by handwaving or postulating Everett/Many-Worlds branches or whatever woo-woo you want. There are other interpretations of the framework that want to salvage pure determinism by insisting on unobservable “hidden variables” that secretly determine how a waveform will collapse, but a guy called John Bell created a thought experiment to test that and eventually someone actually ran the experiment for realsies and basically if there are hidden variables, they can’t be “local” which I roughly understand as a fancy physics word that means ‘dependent on spacetime coordinates’. Hidden variable theories totally work in non-local interpretations of QM (e.g. see “Bohmian pilot wave model”), but many physicist don’t like those because it causes (even more) problems with General Relativity.
TL;DR / to sum up:
If there are no hidden variables in QM/QFT, then randomness is an intrinsic and foundational aspect of reality, so after “rewinding” the universe, differences will eventually accumulate due to differences in the way that the waveform of subatomic particles collapse.
I’d recommend reading Stephen Wolfram on this question. For instance: https://www.wolframscience.com/nks/p315--the-intrinsic-generation-of-randomness/
I understand that if you do this, quantum processes which happen constantly for every atom you cloned have random outcomes. If the universe is a simulation you could force the RNG seed to be the same and get the same outcome, but assuming you have to copy the earth as the “user” of this universe by some enormous equipment that prints all the atoms in about the same place, you can’t do that.
You also have the issue that you couldn’t print everything at once in the same instant so the copied earth will evolve with time different from the original., and also you probably have to destroy the original to make the copy. (Destructive scanning)
Also Heisenberg uncertainty means your atom printers are only approximate, there is a limit on how accurate they can be.
Note also that atom printers won’t actually work by current understanding of chemistry, it’s just a thought experiment.
Did you just show that nanotechnology/atomic precision machines for creating things are impossible?
No. An atom printer is a machine that has ’little bitty fingers” that just puts atoms in place on a surface and builds a whole planet layer by layer. Like how a 3d printer works
This is invalid—you cannot leave atoms in states that are not stable chemistry wise. This came up in the Drexler Smalley debate
nanotechnology/atomic precision machines would have to use a method more like what nature uses. You have shaped catalysts and you mechanically allow in specific precursor molecules into the catalyst ‘press’. The catalyst is shaped so that side products are not possible.
After bonding, the press ejects any waste molecules down one path, and sends the new molecule down another. There are then further additions—it is essentially the same thing as sequential organic chemistry synthesis, except that there are almost never side products. (when a side reaction happens it can permanent block that particular nanoassembly line—you need more than in parallel 1 for every process)
Later in the process, these large molecules are convergently assembled with each other, in a manner similar to how ribosomes work, to form even larger molecules, and then those are combined and so on.
There are major limitations to this approach. You cannot “print” anything, you can only make specific parts you have an assembly path for. (though at the higher levels of assembly you have many possible options, similar to how there are a very large number of valid proteins a ribosome can build).
It means you cannot “print” the rocks and living creatures of a planet.