Is time fundamental to nature, or just an illusion?

Question

Curious to know if time is fundamental to nature, or just an illusion?

We measure time by observing physical changes, increasing or decreasing disorder.When there is no change, there is no perceived time.

UPDATED QUESTION at request of moderator to make it more specific: Is time an independent field, perhaps attributable to specific particles, like mass or electromagnetic forces, or time 'simply' a way we track changes in matter (entropy?) relative to each other? - best I can do.

I am not a physicist. Layman's terms please. Thanks.

Answer 1

As near as we can tell, time passes even though we might not be present to observe it i.e., the stratigraphic record and radioactive decay both record deep time which passed long before humans were present to study them. In addition, our best knowledge of the structure of the observable universe indicates that the light now reaching our telescopes from the farthest reaches of the universe has been in transit towards us for billions of years.

If the passage of time is an illusion, it is an intricately contrived one, requiring the active intervention of something so clever as to create fake evidence of its passage convincing enough to fool our best minds for hundreds of years.

Answer 2

Yes, time is necessary to our perception of nature, but to see this I will use a more quantum mechanical view of time.

Historically, 3-dimensional space (or since relativity 4-dimensional space-time) has been the playground for physics. Particles, densities, fields, events all exist at coordinate locations in space-time. After all, you see this vast space with your own eyes and can reach out into it. Many questions follow from this picture. Perhaps there are more than 4 dimensions, perhaps space/time is emergent from "events", and your question of perhaps time being illusory?

However, quantum mechanics is not about objects in space-time. Instead it is about objects (kets) that stand for particles and are in a very large dimensional Hilbert space. The Hilbert space is not "space-time". Representations of the Poincare group act on the kets in the Hilbert space to rotate, boost, and translate the kets by the Lie group parameters $\vec{\theta},\vec{\lambda},\vec{x},t$. The Poincare group acts on its own generators by conjugation such that under its rotation subgroup, $\vec{\theta},\vec{\lambda},\vec{x}$ rotate like 3-vectors, and under its Lorentz subgroup, $(\vec{x},t)$ transforms like a 4-vector. It is the space of the Lie Group parameters $(\vec{x},t)$ that is called "space-time".

Now, suppose you decided to do all the physics transformations $\vec{\theta},\vec{\lambda},\vec{x}$ but no time translation t (ie: no waiting). In other words, there is a subset t of Poincare group transformations you decide not to do. Unfortunately, eliminating time transformations from the Poincare Group does not leave a closed subgroup. For example, if you do a sequence of small translations ($x<<1$) and boosts ($\lambda <<1$) in the same direction, you would discover that you had done a little bit of time translation $t=\lambda x$.
$$ e^{\lambda K}e^{x P}e^{-\lambda K}e^{-x P}=e^{\lambda x E}=e^{t E} $$
So even if you thought you got rid of time translation, the product of other group elements would bring it back.

Here is a less mathematical argument. Suppose you have the object "muon". If you wait about 2.2 usec, it decays (changes into other stuff). If instead of waiting, you did the single transformation of rotation, boost, or spatial translation to the muon, it would not have decayed. Waiting is essential to explain our perception of the muon decaying and is therefore not illusory.