How fast is our universe moving?

I am used to resorting to history and the classics, more than anything because everything seems to be invented.

Although we call ourselves super technological and advanced civilization, in reality "as the years go by, life rhymes with ourselves," the poet said last week.

The big questions today and the basic things, the most important, remain the same.

Although our understanding of these fundamentals is evolving and the cosmos rhymes better for us, there are basic concepts that do not move.

And there we are going today, to the movement.

To movement and with respect to what we define it.

A universal reference system, which is the Holy Grail of physics (I confess, I have once again

in the background as I write).

Aristotle already more than 24 centuries ago tried to understand why and how all the things we know move, in space but also in time, that is, they evolve.

He put on the table the concept that every movement has a cause (or a set of them), a force that causes it (I put the force as a physicist) and that the interactions that cause these movements follow one another.

In addition, the famous Greek philosopher raised the need for an immobile entity that was the original engine to explain the movement of everything.

That immobile entity that defines the essence of movement can, in a certain way, be conceived as the reference system, something that illustrious scientists such as Galileo Galilei, Isaac Newton and Albert Einstein thought about a lot.

Leaving aside the more cumbersome discussion about types of reference systems and how physical laws do not change in some of them (or should not change if we understand them correctly), the fact is that movement, its absence, its variation or inertia, must be defined with respect to something.

And this is where I want to stop to describe how our existence is linked to movements that, despite occurring at incredible speeds, go completely unnoticed by us;

If you don't live looking through a telescope, of course.

In the time it takes to read this sentence, about 5 seconds, and if you are in mainland Spain or the Balearic Islands, you have moved about a kilometer and a half.

In the time it takes to read this sentence, about 5 seconds, and if you are in mainland Spain or the Balearic Islands, you have moved about a kilometer and a half.

At intermediate latitudes, the earth's surface moves at a speed of about 1,200 kilometers per hour, each point completing a circumference in about 24 hours of solar time, laugh at Carlos Sainz Jr. or Fernando Alonso, taking as a reference system the one defined through the center of the Earth and its axis of rotation.

In the Canary Islands they go about 20% faster, and if someone were to read us from the South Pole, they would be at rest in that reference system.

The motor, we could even say motors, that causes this movement can be found in far from simple physical concepts such as gravity or angular momentum and its conservation, among others.

The normal thing in our life is that what we take as a reference at some point moves, which shows that it was not a very good choice (and we are not talking about characters who have jumped the game on multiple occasions) or that we mature and find some better.

The same thing happens in the universe.

It turns out that what we took as a reference in the previous paragraph, the center of the Earth and its axis of rotation, also move.

Leaving aside the axis and concentrating only on the first one, the Earth orbits around the Sun, again due to gravity and the conservation of angular momentum, at a whopping almost 30 kilometers per second or just over 107,000 kilometers per hour, a fairly constant speed.

That incredible value is about half the speed of a cap they put on top of a nuclear bomb more than 50 years ago to test whether they could be detonated in a controlled way underground.

The test was not very successful, the cap allegedly volatilized or was ejected into outer space, the fact is that it was never found, but its speed was measured shortly after the explosion.

Recreation of the Parker Solar Probe during one of its approaches to the Sun.NASA

We continue our trip, penultimate stop: the Sun and its surroundings, what is known as the local rest system, which is what is used to measure how everything else in the universe moves with respect to us, we travel to more than 800,000 kilometers per hour (220 km/s) around the center of mass of our galaxy, the Milky Way.

The Sun, in fact, is going a little faster than that, bringing us a little closer to the galactic center and rising above the disk of our galaxy.

This speed is already big words.

Man has not built anything that goes so fast, the record is held by the Parker Solar Probe space probe, which reached 700,000 km/h in 2021, 0.06% the speed of light in a vacuum.

And finally we come to the last movement in which we are immersed without realizing it.

The Milky Way moves at more than 2 million kilometers every hour (around 600 kilometers every second) in the direction of the Leo constellation (strange to put that reference because the constellation "is in our galaxy").

And regarding what?!

Well, the Milky Way moves with respect to what we could consider the complete universe, defined from what fills the entire universe and does not move with respect to it, because it is itself: the cosmic background radiation.

The Milky Way is moving at more than 2 million kilometers every hour (about 600 kilometers every second), and we live thinking that we are standing still!

The photons of that radiation that fills space-time and that were created when the age of the cosmos was only 370,000 years, 0.003% of the current age, do not look the same on one side of the sky as on the opposite.

Some of us eat them warm (they seem to us to be more energetic photons than “normal”), from others we coldly move away (they seem to us to be less energetic photons) due to that peculiar movement of our galaxy in the universe.

And we live thinking that we are still!

And the cosmic background radiation, does it move with respect to something?

Does our universe, let's say the one we can observe, move with respect to something?

Is this cosmic background radiation the immobile engine that Aristotle was looking for?

Is it gravity because it explains all the movements we have described?

If we consider that the cosmic background radiation does not move, how do we understand its relation as a frame of reference to the fact that the universe is expanding, that every second what was once a centimeter of empty space becomes something larger?

And if that space is empty, does it exist?

It has to exist, but nothing fills it, or anything that we know of.

How then is emptiness defined?

Is the Aristotelian motionless motor what the void is?

The truth is that right now I can't take it anymore, I go back to the armchair to watch Indiana Jones finish and pretend I'm still.

Cosmic Void

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