Every time we look at the Universe, we see a small portion of the information available. When we look at a distant object, such as a galaxy or a quasar, we can calculate its distance, measuring its apparent brightness with its apparent magnitude, and determining how far its light has changed in red. That red glow gives us some interesting information: how fast, mainly because of the Universe’s expansion, does this galaxy seem to be slipping away from us?
But you may also be wondering if distant objects seem to be moving too fast for us in our line of sight if they are moving in the opposite direction (or sideways) too? If they did, instead of increasing, could the Universe rotate? And if so, what could be the consequences? This is what Mike DePaul wants to know who writes to ask:
“I enjoy reading your articles on the Universe. Have you ever been asked, ‘Is the universe spinning?’ “
It is a sage idea, and it is well worth it. Let’s find out!
From our vantage point in the Universe, it is essential to remember what we know and cannot perceive. We cannot see all its features when we look at light from a distant object. Of course, we can measure all the photons that come from that object, and a lot of information is coded in that.
We see the total of all the starlight emanating from the stars within.
When electrons drop from high energy levels to low, any molecules or atoms happy will also emit light, which is part of what we see.
Any neutral atoms or molecules interacting between light emitted by our eyes will absorb light; that sign is also pushed into the light we see.
Atmospheric geometry – the bending of space everywhere near the line of sight – also affects light, affecting both how light an object appears and how large it is.
And the expansion of the Universe, as well as the relative movement of the discharge source toward us, is also imprinted on that light, changing its wavelength either by redshift or blueshift.
This gives us a fantastic amount of information that we can work on, but what is missing is an essential piece of information that we would like to have: speed, on the roads that correspond to our line of sight, each item. Moving?
It would help if you remembered the considerable distances between galaxies to understand why this is so. In most cases, all galaxies except the closest galaxies range from tens of billions to billions of light-years. Even if the galaxy were moving too fast in space – say, somewhere around 10% light speed – a change in its position over time would not be noticeable. The 1 billion light-year galaxy is about 10% of the speed of light at your destination; over ten years, it can only change its position in 1 light year.
We can measure one year of light changes in some of the closest stars to our galaxy, as we did with 61-star Cygni: the first star seen to change its position over time. But in a universe about a billion years of light, a difference beyond the current limits of modern astronomy technology would be accompanied by a change in its 0.2 billion arc-second locations over ten years.
Even Andromeda, the giant galaxy in the Milky Way, when we compare the first image (from 1888) with its photographs today, shows that not a single star among them has moved in a way that seems modern. Technology.
