[perihelions]

An implosion-type nuclear weapon can compress matter to some multiple of the density of osmium.

This isn't useful for USPS box packaging; I just think it's neat.

edit: Also, inertial confinement fusion plasmas go up to about 1,000 g/cm³,

https://aip.scitation.org/doi/full/10.1063/5.0008231 ("Unified first-principles equations of state of deuterium-tritium mixtures in the global inertial confinement fusion region")

[andersco]

Thanks for that tip. I am about to ship an implosion-type nuclear device and my first thought was if I could use a USPS flat rate box.

[m463]

Be careful, the shipping rules are tricky.

For example, you need to compress the implosion-type nuclear device with another implosion-type nuclear device first to get it to fit in the box.

[a4isms]

"It's implosion-type devices all the way out."

[ilyagr]

Can this overcompressed material continue to exist at room temperature and pressure?

It would be remarkable, but I guess it's hard to imagine how that could work.

[perihelions]

That's a great question. There's solid phases you can create at extreme pressure that remain stable or metastable at STP, like the diamond allotrope of carbon. I don't know of any examples that retain a high density at low pressure. Is it possible for something like that to exist?

There was a suggestion that hydrogen metal could be metastable at low pressure -- it would be much denser than molecular hydrogen -- but it looks like that's controversial:

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

edit: Turns out diamond is ~70% denser than other forms of carbon, so that's sort of an example. Though its density is pretty low in absolute terms (~3.5 g/cm³).

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

[ilyagr]

Diamonds are a great example!

[Retric]

Especially because they’re slightly unstable at STP and will eventually decay, it’s just slow enough to only be relevant on geologic timescales.

[colechristensen]

If there was a material which could handle the internal stress, sure. That material probably doesn't exist.

Like a balloon exists at STP despite being internally at higher pressure, but balloons also pop. Tempered glass also exists and significantly higher pressure and likewise explodes. Often metal structures will retain some stress (sometimes quite high) after manufacture.

The amount of energy released at some of those other materials if they had the magical property of staying together... would be terrifying if popped.

[bell-cot]

Not really. But if you ship it sufficiently fast, the en-transit expansion won't be enough to matter.

[ilyagr]

I guess if I can get USPS to accept the parcel quickly enough, what happens afterwards is their problem. I'm sure they won't mind.

In fact, if the parcel is - er - damaged while in their care, the USPS will owe me. They better rush.

[b112]

I worked on this a bit, as a joke. A sex doll, in a box, with a small helium tank.

I wanted a friend to open the box, be scared by the air/hissing sound, back away, and before he could react?

Sex doll floats to the 12 foot ceiling in his office.

I had issues with the trigger, it deploying correctly, tried it a dozen times and gave up.

My other concern was it mistakely deploying while in transit with the post office.

[s1artibartfast]

I'm guessing that is a value for a hyper localized volume of the plasma