superposeur

> Many quantum information theorists don’t even believe the wave function is “real” but just a mathematical tool for making predictions about measurement outcomes

You are correct that many say this, but this is a constant source of frustration for me (a physicist who does believe the wave function is the only real thing). These physicists never seem to articulate what then is supposed to actually be “real” (under their definition) or what laws govern the “real” things as opposed to the wave function. Implicit seems to be that there is some kind of separate classical realm that obeys non quantum mechanical laws. Is this separate classical realm to be understood as a macroscopic limit of the quantum realm? But if so then the whole picture is circular since wavefunctions are supposed to be mere bookkeeping devices for classical things.

Or to put this more succinctly, if the wave function is a mere bookkeeping device, then bookkeeping for __what__?

(I should mention that yes I know about QBism and all that and my confusion is not for lack of talking to QBists about such things — I just can’t make heads or tails of what they tell me!)

To the extent that the physical world and consciousness can be modeled as computations (in order to “simulate” on some hardware), the details of the “hardware” running the simulation are totally irrelevant to the occupants of the simulation; only the relational patterns between states of the simulation at different times are relevant. The hardware could run fast or slow; forwards or backwards in “simulation time”; once or multiple times over and over; using grungy calculations or clock time-saving efficient algorithms.

Actually, it’s irrelevant to the occupants of the simulation whether or not the simulation is even “run” or merely has the potential to run. Or, indeed, whether the hardware even exists. Or, indeed, whether we use the word “simulation” instead of “laws of physics” to describe the patterns of relations between simulation states.

It’s hard for me to see how the simulation hypothesis can have any content whatsoever.

Interactions between particles such as quarks are mediated by fields filling the space between them (such as electromagnetic field and gluon field). Ripples in these fields propagate at speed less than or equal to c.

This is a classical picture, but the quantum picture is similar: evolution is generated by a local Hamiltonian constructed out of field operators attached to every point of space.

So, both classically and quantumly, relativity demands the existence of fields filling space to propagate causal influences at finite speed.

Edward Witten bestrides mathematical physics in an Euler-likes way. In math/physics circles, ask the smartest person you know who is the smartest person they know and sooner or later all roads lead to him.

I’ve been making his Nutty Pudding as a lunch for the last few months. It’s easy to prepare, portable, satiating, and scrumptious.

Great Scot! 21.81 Gigawatts!

https://m.youtube.com/watch?v=fzuO9wHrvGg

Relevant quote supporting your point that this is his point:

> Like Uber, the massive investor subsidies for AI have produced a sugar high of temporarily satisfied users.

Asimov Press, a new publishing venture that will produce books + magazines about progress in biotechnology, launches

I agree — it’s a question that takes one right up to the limits of human cognition. Another question like this: “is the universe finite or infinite?” One or the other must be true, yet both options will eventually melt your brain to contemplate.

Well, first, I take it to be an axiomatic goal of science to believe that which is true, disbelieve that which is false and to be agnostic about things we have no evidence about; I.e to calibrate our model of world to the world as it is.

But, further, I’ve seen what happens when a subfield reports its findings in a way that misleadingly raises expectations of a titanic discovery just around the corner. When the discovery fails to materialize, over-optimism curdles into its opposite, over-cynicism. Better to calibrate expectations accurately — slow and steady wins the race.

The “eventually build dna base pairs” (that continue self replicating) is the uncertain and possibly ludicrously improbable step. See for instance https://www.nature.com/articles/s41598-020-58060-0 which argues for a probability per exoplanet small enough that it hasn’t happened a second time in the observable universe. On the other hand, one of the self-organizing proposals cited elsewhere in this thread may turn out to be correct and the probability may be much higher.

The point is that, while there are some cool ideas on the table, everything hinges on the particular value of this probability (not just a qualitative story of how life might have arisen) and we don’t know what it is. Still relevant: https://blogs.scientificamerican.com/cross-check/pssst-dont-...

It is “important to remember” precisely because these days people are not remembering this and speak with a sense of inevitability about discovering life elsewhere, which sense of inevitability is totally unsupported. I may gently point out, your own post says “it is only a matter of time before science can connect the dots”, reflecting this (in my view) distorted sense. The abiogenesis research you cite is absolutely worthwhile, but it is not even clear if it is in the right direction and certainly far, far from successfully sparking the sustained chain reaction of life. To my eye, equally consistent (as some different research may suggest) is that a combinatorial needle must be threaded to the tune of p < 10^-23 per exoplanet, making it unlikely to happen again in our observable universe.

Edit: to cite just the one “combinatorial abiogenesis” reference, see for instance https://www.nature.com/articles/s41598-020-58060-0

Don't mean to pick on words, but your statement that "the math of probability and the simple components to life" makes life elsewhere an "inevitable outcome" proves my point that the dialogue around this topic is currently distorted. The probability of life arising from simple components is totally unknown. Equally likely, sparking life requires a combinatoric threading of a needle to the tune of 10^-25 even when all ingredients are gathered in proximity.

I think it's "worth remembering" precisely because it seems not to be the base case anymore! To see this, just look at all the expressions of confidence in life's ubiquity throughout the rest of this thread!

This is what I referred to as "speculation" in the literature for life's origins on Earth. This speculation is a good first theoretical stab... or it might not be. Until life is created from inorganic matter in a laboratory (enabling us subsequently to estimate how rare or not it might be elsewhere in the observable universe), we should substantially dial back our confidence from "life is likely extremely plentiful throughout the universe at one point in time or another".

Fair enough. On the other hand, to my ear the title "NASA finds life-sparking energy source and molecule" sets the tone, as though life was sparked, or that we even know could be sparked by the presence of these ingredients with some degree of confidence.

Not in general, just on this particular point. Because, in my opinion, we as a scientific community are currently flush with the (very cool) unexpected discovery of so many exoplanets and it is somewhat distorting our collective thinking about life and its origins.

Ah, but in my opinion we can't call 10^-25 a lower limit since, if life didn't occur in this collection of planets, we wouldn't be here asking the question in the first place!

Well, perhaps you know that none of the recent findings are evidence of life, but in my conversations with others I have perceived a great deal of confusion on this point, even among scientifically literate colleagues. Also, the fact that we have zero understanding of the probability of abiogenesis is, in my experience, a greatly under-appreciated fact. I speculate that the way findings are reported contributes to this confusion.

Also, at risk of incurring a flame, I'll gently point out that you are folding into this confusion and reinforcing it with your language: "likely precursors everywhere, habitable bodies" ... we absolutely do not know that these conditions are "likely" precursors, which is a statement about a probability we know nothing about and as for "habitable" we do not actually know anything about whether or not a body is habitable in the sense of likely to spontaneously form life.

This is true. It is also true that we have found “not one single shred of evidence that life has ever existed anywhere in the observable universe but Earth”.

No is declaring that there is no needle in the haystack. Please actually read my post.

I’m certainly not claiming the actual probability is 10^-40 , only using this as an example consistent with an upper limit, which probability would imply life has not arisen a second time in the observable universe. Actually this is way overkill — as you say, even if the probability is as high as 10^-25, life on Earth is still probably the only instance in observable universe. The point is that we have no idea what this all important parameter is.

These factors are what I call the “trappings of life”. It is a completely open question (and I mean completely) how likely life is to arise spontaneously when these factors are present. One single instance of life elsewhere or successful abiogenesis in the lab would change that, but we have neither.

Yes and I’m glad we’re doing it! No life or fossilized remains of life of any kind has yet been found.

I agree, if — that’s an enormous “if”.

If, in a volume of space, there are N exoplanets and 100 spontaneously created life, then I’d crudely estimate the probability of life at 100/N for a given exoplanet.

Currently, we have only an upper limit on the probability and barely even that. All observations are consistent with a probability less that 10^-40, meaning it certainly wouldn’t happen a second time in the observable universe.

This is intriguing and I’m very happy this exploration is being done.

But, for decades, I’ve been reading reports of the discovery of evidence for the trappings of life elsewhere: water and organics and “habitable” exoplanets. These are valuable discoveries, but the tone of the reports suggest they imply life is about to turn up.

It’s worth remembering that there is not one single shred of evidence that life has ever existed anywhere in the observable universe but Earth. Moreover, no one has succeeded in hatching living matter from non living matter and we must honestly say we do not know how this process came about or the faintest estimate of how likely it is to occur (despite much speculation, some of which may turn out to be correct but equally may turn out to be dead wrong). The oft cited fact that life arose “quickly” after the formation of Earth has no bearing on the question.

Almost all physicists have assumed that quantum effects will get rid of the singularity, as you say. The import of this paper is that there is no singularity even without accounting for quantum effects (at least for Kerr black holes and one particular definition of “singularity”).

It turns out that you can only measure one component of the spin vector at a time. So you choose some direction in space, call that direction the “z” direction and orient your Stern-Gerlach apparatus in that direction. Important point: SG only separates two beams along this one direction so is only sensitive to differences in the z component of spin vector. You find two final beams. Effectively the measurement has “snapped” the z component of spin onto one of two discrete values. The system is rotationally symmetric in the sense that you could have arbitrarily chosen any other direction in space to call z and the measurement results would be similar. Indeed it’s very interesting to consider the results of orienting various SG apparati in different directions and then chaining together by feeding output of one as input beam of another (as is imagined in some textbooks).

At a certain threshold, though, it is clear who will win this power struggle. Thereafter, if you do not sign you will be implicitly against the winning team once the dust settles, which is a powerful incentive to sign yourself. Certainly there is genuine feeling that gets the ball rolling, but the fact that it snowballs to 95% can’t necessarily be taken as a sure sign that all 95% would have signed in a secret ballot.