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The passage of time is a universal aspect of life. but what he is Time, and why do we experience it as something that has direction, has a past and a future? In a new study, scientists have broken down the “arrow of time” into a microscopic physical level.
The second law of thermodynamics says that everything tends to go from order to chaos, a process known as entropy that determines the arrow of time. A stronger arrow of time means that it will be more difficult for the system to return to a more orderly state.
“Everything we consider a difference between the past and the future stems primarily from a single principle concerning the universe,” Christopher Lynn, lead author of the study. Lin said his motivation for the study was to “understand how the arrows of time we see in life” fit into this larger idea of entropy on the scale of the entire universe.
Using research previously performed on salamanders, Lin and colleagues at CUNY and Princeton examined how the arrow of time represents the interactions between amphibian neurons in response to watching a movie. their research It will soon be published in the magazine Physical review letters.
On the one hand, it’s fairly obvious that the arrow of time will produce biologically. “To be alive, you have to have an arrow of time because you are developing from a child into an adult, constantly moving and receiving stimuli,” Lynn said. In fact, entropy here is irreversible - you can’t go back.
But what the team found was not something that was self-evident.
Lin and colleagues looked at a separate 2015 study in which researchers were watching salamanders in two different movies. One of them depicts a scene of fish swimming around, similar to what a salamander may encounter in everyday life. As in the real world, the video has a clear arrow of time - that is, if you watch it in reverse, it will look different than if you play it forward. The other video just has a gray screen with a horizontal black bar in the middle of the screen, which quickly moves up and down in a random, tense fashion. This video did not have a clear arrow of time.
Do more complex interactions produce the power of the arrow of time, or are they simpler dynamics?
A key question for the researchers was whether they could identify signs of ‘local reversal’ in interactions between small groups of retinal neurons in response to this stimulus. Are interactions with irreversibility - they would look different if played in reverse, with an “arrow of time” - present in simpler or more complex interactions between neurons?
“You can look at a system and you can ask: Do more complex interactions strongly produce the arrow of time, or are they simpler dynamics?” He said flexible.
The researchers found that interactions between simple pairs of neurons essentially determine the arrow of time, regardless of which movie the salamander watched. In fact, the authors found a stronger time arrow for neurons when the salamander viewed the video with the gray screen and black bar—in other words, the video without a time arrow in its content elicited a larger time arrow in the neurons.
“We naively thought that if a stimulus had a stronger arrow of time, it would appear on the retina,” Lin said. “But it was the other way around. That’s why it was a surprise to us.”
While researchers can’t say for sure what caused this, Lin said it may be because salamanders are more accustomed to seeing something like fish film, and processing the synthetic film requires more energy. In a more turbulent system, which will have a larger arrow of time, more energy is consumed. “Surviving will still determine the arrow of time,” Lin said, regardless of the stimulus.
Lin said some research suggests that in humans, time arrow perception in the human brain may be related to how difficult it is for people to think. Lin said he hopes future research will shed more light on this idea.
“If it is not necessarily the arrow of time in the stimulus that is driving the arrow of time in the retina, then what is driving it?” Asked.
In the end, the experience of the passage of time in the physical body is more complex than it appears. Scientists can use this approach to search for local irreversibility in other contexts as well, where unexpected interactions can be found to produce time.
“It doesn’t just apply to neurons — you can apply this to flocks of birds, or anything where multiple things interact, like populations of bacteria,” Lin said.
“And the answers can be quite different; the arrow of time can come from completely different places, from completely different kinds of interactions.”
Becky Ferreira contributed to this article.