We all think we know what time is. We might even be convinced that we have a good handle on it. But do we really?
Since Einstein, scientists and philosophers have been debating the nature of time and whether or not it even exists outside of our perceptions. Some say yes, some say no, but in this blog post I'm going to try to shed some light on the subject . First, let's talk about Newtonian mechanics...
Newtonian mechanics is also known as the clockwork universe. It's based on Sir Isaac Newton's observations of nature at low speeds and in 'normal' conditions - that is, with relatively large objects moving slowly enough for him to measure their positions accurately using geometry and calculus. It might be surprising to some people, but the whole time thing wasn't really an issue back then; it was just assumed to exist.
To describe his understanding of how things behave, Newton had invented a system of mathematics called calculus (fun fact: he shares credit for this discovery with Gottfried Leibniz).
For centuries before this, mathematicians had been working on new ways to precisely express quantities like length or velocity over time, but it wasn't until calculus was developed that the process could be carried out in a way that physicists and engineers really appreciated.
It opened up new possibilities for describing natural phenomena mathematically, especially when these phenomena were related to motion.
So Newton applied this new system of mathematics to describe how objects move through space and various forces, like how gravity, affect them. But he did more than just describe things. Over time his work led people to the conclusion that everything in nature can eventually be described by motions or interactions between particles, which are called 'particles of matter'.
Atoms themselves weren't confirmed as real physical entities until a century after Newton's death, but once they were finally established as his ideas about their behavior made sense. And so began the atomic theory of matter, which made its own predictions about how particles could interact with each other under certain circumstances.
For Newton, this was enough to explain everything he saw or imagined happening in nature. If you have enough time-based information for a situation, then you can calculate all the forces involved and work out what will happen next just like you can use exactly the same logic to say how long something will take to reach a certain point given its current speed or position on your journey.
These are everyday concepts that we don't even have to think about when it comes to planning our days, but they're extremely powerful ideas when it comes to describing natural phenomena too.
Fast forward nearly two centuries after Newton's death, to the time of Einstein...
Albert Einstein was one of the best-known scientists of all time. He is most famous for his theories of relativity that is, the idea that light travels at a constant speed regardless of how fast you're moving relative to it (and this means that things look longer when you're hurtling past them at high speed).
But back in 1905, when he published his special theory of relativity, Einstein's ideas about clocks and movement were actually based on another scientist's work.
His main area of interest at the time was electromagnetis but at this point in history, nobody had yet proved or observed sparks or electricity passing through empty space between two charged spheres.
This sparked lots of debate and speculation about how such a thing could happen to 'push' or 'pull' other objects into movement. As you might expect, there was no rigorous explanation of what these forces actually did under certain conditions.
Despite this lack of experimental evidence, it didn't mean that the theory wasn't useful; we still use it today for lots of practical purposes.
And given everything we already knew about how electricity and magnetism worked by the early 20th century, Einstein was able to develop his own ideas about how they might interact with each other in different circumstances - just like Newton had done before him!
He used electromagnetism to describe all kinds of systems that involved energy moving through space over time. But unlike Newton, he also used it to describe light, which travels through space without any natural time limit.
Einstein's theories also helped to explain how material particles can behave as waves of electromagnetic energy - and this meant that they could be thought of as existing inside a grid-like pattern called a 'field'.
In some ways, it's easier to think about fields as being like virtual versions of real objects, but you don't need to look too closely under certain circumstances because the field itself appears to dissolve into different things - quite similar to water going from a puddle on your driveway into the rain that falls from the sky above.
It would be wrong to say that Einstein was saying anything new at this point because his ideas drew on known properties of electromagnetism and other fields too; but he was developing the mathematics that could describe all these different things, and ultimately apply to anything else that scientists could observe or experiment with.
For example, Einstein used his field-based theories to explain the behavior of what's called 'matter waves', which is related to how an atom (which is made up of positively charged particles at its core, surrounded by negatively charged 'electrons' whizzing around it) interacts with light rays. If you put enough energy into them, atoms can also be thought of as tiny magnets with north and south poles.
And unlike something like a weight on a piece of string which you can move up and down without changing its shape much, atoms are much more complex structures because the magnetic fields they generate change their shape significantly as they move around.
So was Einstein Wrong About Time?
No, he wasn't. Although this was the dominant story about Einstein's work for nearly 80 years, this is actually incorrect. It has taken a long time to unpick all these misconceptions because different parts of the story are often independently misunderstood by different people. So they have never been properly challenged or questioned before.
To be clear, there are two separate problems here that are really being talked about when you get physicists talking about 'time' in their work: one involves thinking carefully about how different forces might affect each other over short distances (which is what Einstein did), while the other involves understanding how everything else that exists in space must behave over long distances (which was Newton's area of expertise). They're both difficult topics but they're not the same problem at all.
Reference:
https://theconversation.com/from-newton-to-einstein-the-origins-of-general-relativity-50013
