[unavoidable]

I agree, unfathomable. But one interesting thought that I usually entertain is that based on our best estimates there are more stars in the universe than there are grains of sand on Earth. Now imagine every time you step foot on a beach and think - there is potentially a star system for every grain!

https://www.worldatlas.com/articles/are-there-more-grains-of...

[prawn]

Also a bit incredible is that it's believed that in the last 60 years, we've manufactured more transistors than there are grains of sand. Sand grain estimate is 7.5x10^18. Transistor estimate between 1960 and 2018 was 1.3x10^22.

[abiogenesis]

It is ironic that transistors are (kind of) made of sand too.

[Maursault]

> > Sand grain estimate is 7.5x10^18. Transistor estimate between 1960 and 2018 was 1.3x10^22.

> It is ironic that transistors are (kind of) made of sand too.

Shouldn't we have run out of sand years ago?

[Dylan16807]

Every square millimeter on a silicon wafer has fit tens of millions of transistors for a while. Since the wafer is a under a millimeter thick that's about one grain of sand. So we wouldn't have run out even with those numbers.

Also it doesn't have to be sand, exactly, and more than half the earth's crust is silica.

But more importantly, that number is very wrong. https://web.archive.org/web/20150310025854/http://www.hawaii...

Leaving aside the issue of whether 1mm cubed is a good estimate for an 'average' grain, this is only an estimate of beach sand. Also it seems to be underestimating shore length by a lot, 200 million meters when other sources say 1.2 or 1.6 billion meters.

His estimate for beach surface area is 6000 square kilometers.

The sahara alone is 9 million square kilometers, with sand much deeper too. The first estimate I see, just for that one desert, is 1.5e24 grains of sand.

Another way to look at it is that we apparently use 50 billion tons of sand per year. That's less than a thousand square kilometers worth of sahara. And making 10^22 transistors with 2012 tech would take only 750 thousand tons of sand.

[_spduchamp]

Mind blown

[gattr]

On a similar note [1], there is a few times more trees on Earth (ca. 3 trillion) than there are stars in the Milky Way (100-400 billion).

[1] https://eu.usatoday.com/story/news/2015/09/02/earth-three-tr...

[psychoslave]

Thanks, I always love this kind of comparisons giving perspective on big numbers with something familiar to us.

[rixed]

In the _observable_ universe. My understanding is that, as far as we know, there could be an unlimited number of stars beyond that limit.

[raattgift]

That hardly matters. Anything observable is in the observable universe. Anything outside the observable universe is not observable even in principle.

We might in principle be able to see beyond the surface of last scattering using ultracold neutrino or ultra-low-frequency gravitational radiation astronomy some decades from now, but that just gives us a view of the universe before there were molecules (let alone stars and galaxies), and we could only surmise that what we see at such a huge redshift evolved into the sorts of things (galaxies, stars) close to here-and-now. That might justify a "as far as we know" comment like yours; for now, however, it is better to say that we really just don't know because we don't have nearly enough data yet.

Unless there is a violation of Lorentz invariance available to us very near hear-and-now, there is no hope of seeing long distances at our scale factor (which is a spacelike hypersurface in the standard cosmology's comoving frame, which means essentially that it's a collection of things all at the same "time", but that's coordinate time, and in this case the scale factor is the coordinate). Consequently we can't even be certain about highly-redshifted galaxies' fates at a(t)=1. To be sure would need to outrun the metric expansion of space, or equivalently, we would have to move much more quickly towards a cosmologically-redshifted source of the fastest known messengers than those relativistic neutrinos, photons, or gravitational waves that it emits have been moving towards us. There is an enormous amount of indirect evidence that shows that nothing observable moves like that, and plenty of direct tests of the relevant part of the equivalence principle that require Local local invariance everywhere in the universe since the electroweak epoch moments after the hot big bang.

So while most astrophysicists and physical cosmologists would bet that that there is physics like ours at great distances, including "just one metre, or just one megaparsec" (or even much further) outside our Hubble volume, there is no honest way to assign a probability of that being correct at this time. We can only say that it is consistent with the data we have on cosmic inflation (mainly from the cosmic microwave background's inhomogeneities), and it is exceptionally hard to produce a consistent theory allowing for very different physics just beyond the farthest galaxies we can see, yet still match the overwhelming majority of the data we have collected.

https://en.wikipedia.org/wiki/Scale_factor_%28cosmology%29

https://en.wikipedia.org/wiki/Particle_horizon

https://en.wikipedia.org/wiki/Modern_searches_for_Lorentz_vi...

So, the tl;dr is that wondering about what's outside the observable universe might be fun, but it's not scientific because any hypotheses one might generate can never be verified by observation, even in principle, by the very definition of "observable universe". At best we can only hope that the observable universe is bigger than we think today (e.g. by a very surprising resolution to the tensions in the cosmic-distance ladders, by the discovery of wormholes and comparable topological "defects" in the universe, or by the discovery of faster-than-light travel). I happen to hope some of that, but have no honest basis for that hope.