What do you mean by "orbit the universe", exactly?

I mean what I say,but I'm just asking if it's possible. If I knew what becomes of countless hordes of neutrinos which almost never interact,I wouldn't need to ask. It's pretty obvious they will leave our galaxy far behind.

Sorry, I still don't know what it means for something to orbit the universe. The universe is most probably infinite. How do you orbit an infinite thing?

What is the evidence for an infinite universe? An infinite universe would have infinite mass & that might create problems when it eventually contracts into a Big Crunch. I know Big Crunches are out of fashion these days,but we can't rule it out. To say the universe is infinite is a very big assumption,& extraordinary claims require extraordinary evidence.At almost the speed of light,a neutrino could cover an immense distance in 50 billion years.

The evidence is the measurements of the universe's curvature on the large scale. Assuming the large-scale topology of the universe is simple (so no weird huge naturally occuring wormholes, etc), we get 3 main global curvature options: positive, zero, or negative. A finite universe would have positive curvature, like the 3D "surface" of a 4D hypersphere. If the curvature is zero or negative, then space is infinite. Current measurements indicate that the curvature is very close to zero, but possibly negative. That's one reason why the Big Crunch isn't popular these days.

Of course, the universe might have overall positive curvature, and we just happen to live in a huge region of unusual flatness. And we'll never be able to test that (without FTL travel or information transferal). But if the universe is more curved just beyond our observable universe, there'd be noticeable effects within the observable universe, and we don't see those.

My question seems to have got an interesting debate going,& that's good. Without such debate we could find ourselves in the same sort of situation that existed for a 1000 years after Ptolemy proposed his purely imaginary epicycles to explain the motion of Mars as it orbited the Earth. We need to question our assuptions from time to time.

@MichaelWalsby I admit that it's interesting to talk about whether the universe is finite or not, and if a Big Crunch or Big Bounce is possible, given what we know about the expansion & energy density. But we are getting rather off-topic regarding your neutrino question. ;)

But anyway, whether the universe is finite or infinite, neutrinos can just keep going. They don't need to orbit anything.

It's actually not easy for stellar or supernova neutrinos to orbit stuff, apart from black holes, and possibly neutron stars. They're just going way too fast to have closed orbits around less extreme gravity sources.

OTOH, neutrinos in the CNB (cosmic neutrino background) are much slower, so I guess they could get trapped into orbits around regular stars. But we don't have the technology to detect those ones, even if they pass through our best neutrino detectors.

If the universe does have positive curvature, and the expansion rate is slow enough, then neutrinos (and indeed photons) could "circumnavigate" the universe: if you draw a straight line in any direction, and extend it far enough, you eventually get back to where you started from. Just like a plane flying a great circle route on Earth, eg going around the Equator.

But as far as we can tell from current measurements, that's not possible in our universe, because space is expanding too fast.

@MichaelWalsby That stuff I posted is in 6 separate posts. Yes, chat is somewhat limited, and many people have suggested various improvements, to no avail. You can read some info about using chat here.

OTOH, the chat rooms have some advantages over comments, eg you can reply directly to previous posts. You can display images here, by posting a message just containing the image URL, eg

And certain links give you a preview of the page, eg Wikipedia links.