Hacker News Reader

Comment by WatchDog | Hacker News Reader

Is single atom thick gold somewhat optically transparent?

Definitely yes. Gold is surprisingly transparent for a metal. Famously, gold plating is used on astronaut helmet visors, at 200 nm thickness - i.e. ~1200 atoms thick.

Is it more transparent than other metals? How transparent is a 200 nm film of iron or aluminium?

Not transparent at all on visible light wavelengths. Light transmission in metals obeys the skin effect, which means that AC fields (such as the fields in light) do not like to penetrate deep into the material, and the skin depth for visible light wavelengths in most metals is expressed in individual nanometers.

TIL! Thank you for sharing - love me my chemistry after all...

For those who are curious: it fends off harmful EM radiation

https://spinoff.nasa.gov/spinoff1997/hm2.html#:~:text=A%20th....

It is also used as a coating for window panes, as it‘s great at reflecting infrared radiation (reducing heat loss). My father‘s house has such windows.

Are those windows expensive?

Yes, but mostly because of the manufacturing process (requires a vacuum).

Stealth aircraft also use gold-plated canopies to a) contain emissions from the cockpit to the cockpit b) reflect incoming radiation of a well-defined surface instead of whatever mess is inside the cockpit.

I would suspect it is essentially invisible to the naked eye.

It likely only exists in extremely specific conditions, not just like a sheet.

I’m guessing it’s somewhat similar to a microscopic layer around a material that we never notice.

Thin gold layers are green, this looks red if you look at the beaker.

There are spectral data available in the original publication https://www.nature.com/articles/s44160-024-00518-4

If I am reading that right, the beaker is filled with lots of sheets and clumps of sheets not just a single one. So, it’s not clear what if anything a single sheet would look like.

I think gold reflects red light, so it lets greenish light through if you use it as a filter.

I mean, matter is mostly empty space…

Only if you really distort the definitions. The "empty space" you are thinking about is the matter. You can't just put other stuff there.

There's a similar wrong meme about how you never really "touch" anything.

> There's a similar wrong meme about how you never really "touch" anything.

Ok, what is the exact moment you touch something? How close do the atoms need to be?

When weak interaction starts happening.

When does the weak interaction stop happening?

High energies, about three orders of magnitude higher than the LHC produces. (If you squint.)

How about this: two objects are touching when the interaction forces between the objects are of similar magnitude to the interatomic forces within the objects. Very generally speaking, this will happen when the distance between the objects is about the same as the distance between atoms within the objects.

Ok, so I conclude from this that touching is not an exact science.

To be somewhat pedantic: "touching" is a word. The extent to which it is or is not an "exact science" depends on what is meant by "touching", and by "exact science". The definition I gave of "touching" could be made arbitrarily more precise by specifying more precisely the interaction forces under consideration, and the level of precision to which one should compare their magnitudes. What you mean by "exact science" is something I cannot guess at with any useful level of precision. Whether or not any of this has any bearing on the original topic of discussion is another matter.

I mean, the actual interaction force that defines "touching" is open for debate. Touching is an abstract concept, removed from actual physics.

That was sort of my point. If we use a definition of "touching" that is relevant to the atomic scale, whatever that definition is, we can reasonably talk about what "touching" means at an atomic scale. If we use a colloquial definition of "touching" which is meaningful for macroscopic objects but not at the atomic scale, it doesn't make sense to talk about "touching" at the atomic scale.

Do this for 'touching fire' to clarify the actual issue.

There isn't an exact moment, any more than there is an exact height that is "tall". And yet, tall people exist.

The tallest person in the world will say that only normal and short people exist.

I'd bet very good money that they wouldn't say that, no

except protons. These are infinitely dense

Reply on news.ycombinator.com