Does time exist? The answer to this question is obvious. Look at a clock or calendar.
The existence of time is an open possibility, and one that we should take seriously.
What would that mean? It will take a little while to explain, but don't worry: Even if time doesn't exist, our lives will go on as usual.
There is a crisis in physics. For the past century or so, we have explained the universe with two wildly successful physical theories.
General relativity describes the big picture of gravity and how objects move.
Both theories work well, but they are thought to conflict with one another. Scientists generally agree that a new, more general theory is needed for the conflict.
Physicists want to replace general relativity and quantum mechanics with a theory of quantum gravity. The theory explains how gravity works at the smallest scale of particles.
Producing a theory of quantum gravity is difficult.
The string theory is an attempt to overcome the conflict between the two theories. The strings vibrate in as many as 11 dimensions.
string theory is facing more difficulty. There are a range of models that describe a universe broadly like our own, but they don't really make any clear predictions that can be tested.
Physicists came up with a range of new mathematical approaches to quantum gravity after they became dissatisfied with string theory.
One of the most prominent of these is loop quantum gravity, which proposes that the fabric of space and time is made of a network of extremely small chunks.
loop quantum gravity appears to eliminate time completely.
A number of other approaches also seem to remove time as a fundamental aspect of reality.
We know we need a new physical theory to explain the universe, but it might not have time.
Suppose the theory is correct. Would it follow that time?
It is complicated and depends on what we mean.
Tables, chairs, and people are included in theories of physics, but we still accept them.
Why? We assume that such things exist at a higher level than the physics describes.
The tables are from an underlying physics of particles around the universe.
We have a good idea of how a table can be made out of fundamental particles, but we don't know how time can be made out of something more fundamental.
It is not clear if we can assume time exists, unless we can come up with a good account of how it happens.
Time may not exist at any level.
It's like saying there are no tables at all.
Trying to get by in a world without tables might be difficult, but managing in a world without time seems disastrous.
Our lives are built over time. We plan for the future because of what we know about the past. We hold people accountable for their past actions, with an eye to disciplining them later on.
We believe ourselves to be agents because we can plan to act in a way that will bring about changes in the future.
When there is no future to act for, what is the point of acting?
What is the point of punishing someone for a past action if there is no past action at all?
The world would grind to a halt if time did not exist. We wouldn't have a reason to get out of bed.
There is a way out of this mess.
It seems that the sense in which one thing can bring about another is unaffected by physics.
Causation and not time are the basic features of our universe according to physics.
Agency can still survive if that is correct. It is possible to reconstruct a sense of agency completely in terms of causality.
In our new book, we argue that.
The discovery that time does not exist may not have a direct impact on our lives.
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