What can we know about the very large and the very small?
When we start to prod the world immediately around us to see what happens, we come across objects such as rocks, liquids such as water and gases such as air. All very familiar stuff. Generally these things do what we have been led to expect. If we throw a ball then we can knock a can off a wall at some distance away.
Over the generations, people have found formal rules to describe how things behave in different circumstances, such as Newton’s laws of motion or the laws of fluid dynamics. which enable us to predict the behaviour of planets in orbit round the sun or enable us to design an efficient aircraft. The details of these rules are sometimes difficult to understand but, generally, Nature appears to behave in a logical and predictable way. Even if we encounter a new phenomenon, we can usually find a “rational explanation” for it or believe that such an explanation exists even if it eludes us.
Moving out to the Cosmic Scale.
If we change our perspective and look at what happens on the Cosmic scale, we find things are not so intuitive. Although we can usually still find explanations for what we see and measure, they are not what we would naively expect and are often very alien to us.
For example:
- The Earth is hurtling around the Sun at ~30 km/s, yet we feel stationary.
- Time runs at different rates depending on the speed the observer is travelling and strength of the gravity in their environment.
- Space can be curved.
- A straight line in curved spacetime can look bent to us.
The theory of General Relativity, which predicts some of the weirder of these effects has been highly successful in predicting all manner of Cosmic events including Black Holes and the evolution of stars. Using the mathematical models gives very good predictions of how the universe behaves but the meaning of the models are not ones which can be easily visualised. What does it even mean to say that space can be curved?
Our brains are optimised to be good at throwing rocks, catching prey, and navigating landscapes or other activities which would aid our survival in the environment we evolved in. There was no survival advantage in understanding how stars are formed or the concept of space and time being “curved”.
As we look at situations which are further from the environment we were designed to function in, the “weirder” reality seems to become.
Diving into the Atomic Scale
Delving into what everyday objects are made of lead to observations which are at least as “weird” and whose models are at least as unintuitive.
It was discovered that all material is made up of atoms in various arrangements and that these atoms take up only a miniscule volume of that material. Even the hardest and heaviest of materials is predominantly empty space. Although that is not obvious to the casual observer or directly observable without special equipment, there is little yet which would be considered “weird” or which would feel alien to what we see in the world around us.
In the 19th century, atoms were thought of as having a central positively charged nucleus surrounded by orbiting negative electrons analogous to planets orbiting the sun in the solar system but with the electrostatic force replacing gravity [Larmour 1897]. This was a picture which was familiar to many people and so an attractive path to explore but it soon became clear that this was not a correct one. The theory which worked was much “weirder”.
Moving into the sub-atomic scale
We can investigate what atoms are made of but, just as when we look at the cosmic scale, we move further away from the familiar and from what is intuitive to us.
Sub-atomic particles do not behave like planets or like tiny billiard balls with definite properties. Instead, physics describes an unfamiliar world governed by probabilities, uncertainty, and phenomena so strange that even Einstein resisted accepting them.
For example:
- We cannot know for sure the location of an object, only the probability of finding it at a specific location if we look.
- A particle, such as an electron. can travel through two slits at once and then recombine in a way which would be expected for a wave.
- Two or more particles can become entangled such that, even if they are a huge distance apart, a measurement of one will instantaneously cause a change in the other..
Again, as we start to look at phenomena which are at scales which our brains were not designed to directly understand, we come up against models which work to make predictions but which are not clearly understood. In fact, Richard Feynman famously stated in his book The Character of Physical Law (1995), “I think I can safely say that nobody understands quantum mechanics.” In 1952, Niels Bohr said: “Those who are not shocked when they first come across quantum theory cannot possibly have understood it.”.