What time is it?
Imagine that time is passing backwards. People were getting younger rather than old, and after a long life of gradual renewal – without knowing everything they knew – they would end up in a twinkle in their parents’ eyes. This time as shown in A novel by science fiction writer Philip K. rooster But surprisingly, the direction of time is also an issue that cosmologists grapple with.
While we consider time to have a certain direction, physicists do not: most natural laws are “time reversible” which means they would work just fine if time was defined as going backwards. Why does time always advance? And will you always do that?
Does time have a beginning?
Any universal concept of time must ultimately be based on the evolution of the universe itself. When you look at the universe, you see events that happened in the past – it takes a long time to get to us. In fact, even the simplest observations can help us understand cosmic time: for example, the fact that The night sky is dark. If the universe had an infinite past and was infinite in extent, the night sky would be just as bright – filled with light from the infinite number of stars in the universe that has always existed.
For a long time, scientists, including Albert Einstein, believed that the universe is constant and infinite. Notes have since shown It is actually expanding at an accelerating rate. This means that it must have arisen from a more compact state we call the Big Bang, which means that time has a beginning. In fact, if we look for light old enough, we can even see the radiation of the remnants of the Big Bang – the cosmic microwave background. Realizing this was a first step in determining the age of the universe (see below).
But there is a hitch, Einstein’s special theory of relativity makes it clear Time is relative: The faster you move for me, the slower time will pass for you in relation to my perception of time. So in our universe of expanding galaxies, spinning stars and swirling planets, the experiences of time are different: everything in the past, present and future is relative.
It turns out that since on average the universe is the same everywhere, and on average looks the same in every direction, there are cosmic time. To measure this, all we have to do is measure the properties of the cosmic microwave background. Cosmologists have used this to determine the age of the universe: its cosmic age. It turns out that the age of the universe is 13.799 billion years.
So we know that time probably started during the Big Bang. But there remains one annoying question: What exactly? He is time?
To decipher this question, we have to look at the basic properties of space and time. In the dimensions of space, you can move forward and backward; Passengers experience this every day. But time is different, it has a direction, you always go forward, never reverse. Why is the time dimension irreversible? This is one of the main unsolved problems in physics.
To explain why time itself is irreversible, we need to find processes in nature that are also irreversible. One of the few concepts in physics (and life!) is that things tend to get less “tidy” over time. Half this using a file A physical property called entropy It encodes how to arrange something.
Imagine a box of gas in which all the particles were initially placed in one corner (an ordered state). Over time they will naturally seek to fill the entire box (a state of turbulence) – and returning the particles to an ordered state takes energy. This is irreversible. It’s like cracking an egg to make an omelette. Once it spreads and fills the pan, it will never return to its egg shape. The same applies to the universe: as it evolves, the total entropy increases.
It turns out that entropy is a good way to explain the arrow of time. And though it may seem that the universe is becoming more, not less, orderly — moving from a land sea with relatively uniformly spread hot gas in its early stages to stars, planets, humans, and time-related articles — it can nevertheless be growing in disorder. That’s because gravity associated with large clumps may pull matter into seemingly orderly states—with increasing chaos we think must be somehow hidden in gravitational fields. So chaos can grow even though we don’t see it.
But given nature’s tendency to favor chaos, why did the universe begin in such an orderly state in the first place? This is still considered a mystery. Some researchers argue that the Big Bang may not even have been the beginning, in fact it may have been parallel universes Where time passes in different directions.
Will time expire?
Time has a beginning, but whether it will have an end depends on the nature dark energy This causes it to expand at an accelerated rate. The rate of this expansion may eventually tear the universe apart, forcing it to end in a Great Rip. Alternatively, dark energy may decay, reversing the Big Bang and ending the universe in a major crisis. Or the universe may expand forever.
But will any of these future scenarios ever come to an end? Well, according to the strange rules of quantum mechanics, tiny random particles can pop out of a vacuum temporarily, something that is constantly seen in particle physics experiments. Some have argued that dark energy Such “quantitative fluctuations” can cause Resulting in a new big explosion, we end our timeline and start a new one. While this is highly speculative and highly unlikely, what we know is only when we do it Understanding dark energy Will we know the fate of the universe?
So what is the most likely outcome? Only time will prove it.
Conclusion: What is time, and why is it moving forward? Cosmologist Thomas Kitching of University College London explains how the arrow of time points to the future.