• Question: This is my dads question: If you take a (very strong) jar up into space, and literally bottle up some space, would there be a vacuum inside, or dark matter, or both?

    Asked by anon-257942 on 25 Jun 2020.
    • Photo: John Davies

      John Davies answered on 25 Jun 2020:

      The air in the jam jar would rush out when you took off the lid. If you then put the lid back on and brought it home then it would still have no air inside, so it would be a vacuum.

      Dark matter is an theoretical concept used to explain the properties of entire galaxies. We think it must exist, but we cannot see it (hence ‘dark’ matter). However a jamjar is a very small thing compared with the volume of a galaxy so you wouldn’t see anything inside the jar. I will leave it to some theoretical physicist to say if there might be a very tiny-tiny-tiny-tiny amount of dark matter in the jar.

    • Photo: Julian Onions

      Julian Onions answered on 25 Jun 2020:

      On the second – it might… but not in a useful way. Dark matter doesn’t interact with normal matter – so it just doesn’t really see it. So if you took a jam jar into space, dark matter would drift through the jar, but it would keep it, as it would go straight out through the walls. When you brought it back to earth, dark matter would continue to drift in and out of the jar, so in a sense it would have some in it.

      It would be like taking a glass jam jar into space to catch some light, light might pass through it, and light would continue to pass through it on earth!

    • Photo: Scott Lawrie

      Scott Lawrie answered on 26 Jun 2020:

      Yes! If you had a strong enough jar (especially the lid and the seal where the lid meets the jar), you could bring a vacuum back down to Earth. As in: the jar would be completely empty. However as they say, “nature abhors a vacuum”, so it would actually be very difficult.

      I work on vacuum systems (i.e. making really good vacuum here on earth) using very clever pumps to remove all the air from big metal cans. It’s relatively easy (but expensive!) to get really good seals around all the edges and suck down to one hundred billionth of atmospheric pressue. However as soon as you turn the pumps off, the pressure rockets back up again! No seal is perfect and tiny amounts of air can seep through atomic-sized cracks. Also, the walls of the can itself ‘evaporate’ atoms into a perfect vacuum, no matter how good your seals are.

      Maybe astronauts could weld a jar closed (I don’t know if that would work in space though…) to trap a vacuum and you’d have a cute little desk toy of nothingness. What would you do with it, though…?

    • Photo: Susan Cartwright

      Susan Cartwright answered on 29 Jun 2020: last edited 29 Jun 2020 12:57 pm

      There would be a near-total vacuum inside, because space is basically a vacuum.

      There would also be dark matter inside, assuming that dark matter is an undiscovered type of particle. However, the dark matter would not STAY inside: because dark matter is only weakly interacting, it would not interact with the walls of the jar and would pass straight through (and stright through the Earth as well). Dark matter particles travel at around 200 km/s, so any individual dark matter particle would not stay in the jar very long!

      Similarly, there would be neutrinos inside the jar (both from the Sun and from the Big Bang), but they are travelling even faster and will stay in the jar for an even shorter time. On average, there are about 350 neutrinos from the Big Bang in every cubic centimetre of space, throughout the universe (including inside you and your dad).

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