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So much in the universe spins. Could the universe itself be spinning?

Pat French
Telford, Shropshire, UK

If there is only one universe, then there is nothing to relate to its movement; there is no backdrop against which its rotation can ever be observed.

Imagine that you are in the ballroom of a cruise ship at night. Nothing is visible through the portholes. You can see the glitter ball rotating in the centre of the ceiling. You can see the dancers moving in various circles with reference to each other and to the walls of the room, but you can鈥檛 see whether the ship is sailing in circles or a straight line.

However, if the ship is circling so fast that you can experience a centrifugal force pushing you outwards, this might tell you that it is indeed circling.

Unfortunately, even if a centrifugal force is present (and possibly contributing to our ever-expanding universe), we can鈥檛 measure it 鈥� yet.

We would need instruments that could measure tiny changes compared with another observed universe

If there is more than one universe, then we must wait until the others are observed and judge the movement of 鈥渙ur鈥� universe relative to those.

Our little galaxy, the Milky Way, takes 200 million years to rotate once. We can measure that rotation.

For the rotation of the entire universe, we would need instruments that could measure incredibly tiny changes compared with another observed universe over immense timescales at a distance representing the dawn of time.

We can鈥檛 measure that 鈥� yet.

David Bortin
Whittier, California, US

I think that, in general, 鈥渉ave angular momentum鈥� is a preferred equivalent term to 鈥渂e spinning鈥�.

It is widely (but not unanimously) accepted among scientists and philosophers that the concept that electrons and other particles are actually spinning 鈥� and at velocities faster than the speed of light, no less 鈥� is a paradoxical one.

But the term 鈥渆lectron spin鈥� was adopted because these particles do, incontrovertibly, exhibit angular momentum, which would be observed as spinning in macroscopic objects.

The principle that angular momentum must be conserved is often illustrated by the statement that the angular momentum of a planet, manifested as rotation or spin, must equal the sum of the angular momenta of all its constituent particles and parts. It would follow, by inference and extrapolation, that yes, our entire physical universe must be spinning as well. Or it must, at least, have angular momentum.

What our universe is spinning in relation to is, much like the spin of an electron, a bit of a philosophical riddle.

John Hastings
Whittlesey, Cambridgeshire, UK

Mach鈥檚 principle holds that rotation is determined by the overall distribution of matter. For example, Earth is rotating with respect to the background of 鈥渇ixed鈥� stars. Our Milky Way galaxy is spinning in relation to the background of all the other galaxies.

If the universe is infinite, there is no background against which the universe could rotate.

If our universe is finite, but there are no other universes, Mach鈥檚 principle (if it is true) would imply that the universe can鈥檛 be spinning.

If our universe exists in a multiverse, it could be rotating with respect to the background of other universes, but since we can鈥檛 observe any other universes, how could we discern whether the universe is rotating?

There are two ways we can tell that Earth is rotating (other than by observing the daily movement of the stars from our perspective). One is to , which oscillates in a fixed plane while Earth rotates around it. The second is to measure Earth and note that it bulges at the equator due to the centrifugal force produced by the planet鈥檚 rotation.

So we would need an internal observation or experiment that demonstrates the rotation of our universe. (Does the universe 鈥渂ulge鈥� at its 鈥渆quator鈥�?)

Hillary Shaw
Newport, Shropshire, UK

If the universe were spinning, it would have an axis of spin, whether it were spinning in some wider 3D space or as the 3D 鈥渟urface鈥� of a 4D hypersphere. This would create a centrifugal force that would be weaker towards the spin axis.

In turn, the apparent gravity (that is, gravity minus the centrifugal spin effect) slowing the universe鈥檚 expansion would be stronger at the spin axis and we could observe differences in the expansion rate (i.e. different redshifts of stars) in different parts of the universe.

But we don鈥檛.

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