[Hamcha]

Depends how you measure it. Any X kg/lbs of matter here on earth is still that same X kg/lbs everywhere in the universe. Assuming the scale being used to weight is correctly calibrated to whatever planet it's in, it would still show up as the same amount of kg/lbs.

[tialaramex]

This is why simple balances are such a brilliant idea despite their simplicity. You don't need to calibrate to the local conditions, if I have a 250g mass on one side, and I put something on the other side and it balances, that's 250 grams, done. Only the (often provided with the balance) prototype masses need to be calibrated and that can be done by experts far from your local environment.

Until as recently as 2019 this approach - using a prototype - was the only extant mass definition, the prototype kilogram lived at a specialised laboratory and its clones were used around the world to define mass (yes including the pound if you're an American).

[ Today instead the Planck constant is defined to be exactly 6.62607015×10^−34 kg x m^2 per second and it's possible to build devices such as a Kibble balance to estimate what the kilogram is from knowing this definition, the better your Kibble balance the better the estimate ]

[a9h74j]

Depends upon what you set out to measure. lbs is specifically a unit of force. kg is specifically a unit of mass. It is a category error to equate these as measures, although (in many places) an everyday convention to do so on Earth.

IIRC the English unit for mass is the slug. If the tecnical limit is 70lbs or so, that is must technically be read as lbs force -- aka force of gravity which varies with location.

[dragonwriter]

> lbs is specifically a unit of force

Incorrect. The avoirdupois pound (lb) is historically a unit reflecting the long conflation of mass and force, but the modern unit of that name is expressly a mass unit that is a derived unit of the kilogram. The corresponding unit for force is the pound-force, (lbf).

[zmgsabst]

Wikipedia lists it as a unit of mass — as defined by the amount that exerts a certain force.

https://en.wikipedia.org/wiki/Pound_(mass)

The pound unit of force is abbreviated ‘lbf’.

https://en.wikipedia.org/wiki/Pound_(force)

[rzzzt]

Kilopond or kilogram-force is the force with which a 1 kg object is pushing on its base: https://en.wikipedia.org/wiki/Kilogram-force

[jrochkind1]

you could really take USPS for a ride by shipping something to Venus!

[grog454]

"a teaspoon of neutron star material would weigh around a billion tonnes."

https://astronomy.swin.edu.au/cosmos/n/neutron+star#:~:text=....

[droopyEyelids]

It would be impossible to put neutron star material inside a cardboard box, and the original post was talking about possibility.

[ben_w]

If I remember right, given that free neutrons aren’t stable and have a very short half life, it would be explosively unwise even if it was physically possible.

[deepspace]

Yes, a free neutron decays to a proton, an electron and an electron neutrino with a half life of 879 seconds. This decay releases 0.8MeV of energy (mostly in the form of kinetic energy of the electron).

My back of the envelope calculation shows that 1 gram of neutronium (approximately a mole) will release 43MW of energy continuously. Multiply that by 10^14 (the number of grams of neutronium per teaspoon) and the resultant energy release would be unimaginably huge. 'Explosively' does not even begin to describe it.

[grog454]

Actually, it too was talking about impossibility (see title); a much stronger assertion and usually wrong.

[midasuni]

I assume they were saying

Densest material on earth

There are denser materials, but you would struggle to send them via UPS