Time has occupied the greatest minds for centuries and we’re still none the wiser about its absolute nature.
Although there’s nothing in physics that says time must flow in a certain direction, nor precisely what time is, we can generally agree that it’s a very real property of the Universe.
The two bastions of modern physics, General Relativity and quantum mechanics, view time in different ways. In relativity, time is regarded as a coordinate – much like the three spatial coordinates.
Einstein showed that these are intimately linked and that the progression of time is relative, not absolute. This means that the faster you travel, the more time slows down compared to someone ‘stationary’.
Bizarrely, a photon travelling at the speed of light experiences no passage of time at all. For it, everything happens simultaneously!
Quantum mechanics, which deals with the macroscopic world, views time as merely a fundamental parameter; an unvarying and unidirectional flow from the past to the future, separate from the dimensions of space and separate from the object (for example, a particle).
This difference puts these two great theories at odds, and is one of the problems facing physicists trying to unite gravity and quantum theories into one ‘grand unified theory’.
Crucially, however, neither General Relativity nor quantum mechanics regard time as a ‘field’ – a physical quantity that permeates space and has the ability to influence the properties of certain particles.
Each of the four fundamental force fields (gravity, electromagnetism, the strong nuclear force and the weak nuclear force) involve an exchange of particles.
These can be viewed as ‘carrying’ the force. In electromagnetism it’s the photon that’s the ‘force carrier’, whereas the strong interaction is carried by particles called ‘gluons’.
In gravity it’s the (as yet undiscovered) ‘graviton’ that carries the force, although there’s currently no fully successful quantum description of gravity.
Other ‘fields’ imbue particles with certain properties. The Higgs field, for example, involves the exchange of Higgs bosons and gives particles their mass.
In physics, time, whatever its precise nature, is fundamentally different to a ‘field’. It isn’t a physical quantity (like charge or mass, for example), doesn’t impart a force, or determine the interactions of particles.
Hence, in modern physics, time isn’t defined by a mediating particle like the four fundamental forces of nature. There’s no need (or indeed sense) for a ‘time particle’.
Oddly, recent research has suggested that time may actually be an illusion. This odd idea relies on quantum ‘entanglement’, whereby the quantum states of particles are inextricably linked, no matter how far apart they are.
This article is an answer to the question (asked by Brian Roche, from Corke, Ireland) 'Could there be a time particle?'
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