Take a moment to mull that over. How does now unstick itself and become the past, and when does the future morph into the present? How do these states transition, one into another, so seamlessly?

Something remarkable will happen when the clock ticks from 11:59 to 12:00 AM. In an instant, 2019, once all-encompassing, will recede into the past, and 2020, previously futuristic and far away, will step in to take its place.

At any given moment, it feels like we're in the midst of right now. For centuries, philosophers , neuroscientists, psychologists, and physicists have been dwelling on this problem, because of how powerful the experience is; right now is tightly intertwined with the experience of consciousness. Take a moment to just sit and be. There you are. Where? Right now.

By using science to realize that, technically speaking, right now is miniscule, we might be able to stop getting lost in the despair of the present.

This isn’t to say we should become chrono-nihilists who throw up our hands over time being a construct. There's another way to use these facts to recalibrate our understanding of right now to provide a fresh perspective. The way we think about the present, and how long we think it is, can influence our outlook on life, as well as our behavior. Thinking of ourselves in suspended animation, in a present that’s never ending, is not only wrong according to research on the matter, but also isn't helping us make the best decisions for ourselves or each other.

On a holiday dedicated to celebrating the passage of time, as we enter a new year and a new now, let's take this line of questioning seriously, and literally. This year felt impossibly long, but science tells us that right now is actually much, much shorter than it feels when we're trudging through it. Neuroscientists' best estimate for "right now" is only about 2.5 to 3 seconds, or less. According to physics, right now is an illusion altogether.

Even without doing any complicated research, we can intuitively get close to the answer, said Marc Wittmann, a time researcher at the Institute for Frontier Areas of Psychology and Mental Health in Germany.

Luckily, since James and Augustine, science has come up with different methods of investigating "now."

"The present isn’t something we stumble into and through," science writer Alan Burdick wrote in his book, Why Time Flies, of James' specious present. “It’s something we create for ourselves over and over again, moment by moment."

Unlike Augustine, James arrived at the notion that all experience of time is a perception, including the present. Any sense of time that we have, including right now is a subjective, psychological time—what he called the "specious present."

Psychologist William James also grappled with the nature of right now, calling it one of mankind's most baffling experiences. “Where is it, this present? It has melted in our grasp, fled there we could touch it, gone in the instant of becoming.”

After some anguish, Augustine concluded that only the present is real, and that the past and future simply exist in our minds. (This is a philosophy now called presentism.) The past is just a memory, the present is direct experience, and the future is expectation.

Saint Augustine knew this was a difficult concept to grapple with back around 400 AD when he wrote his autobiographical book, Confessions. "What, then, is time? If no one asks me, I know what it is. If I wish to explain it to him who asks me, I do not know."

It's an issue referred to as "temporal binding," and it's an elegant proposition for a definition of right now: Right now is the window of time when your brain will experience inputs from the world as simultaneous.

The brain has to wait for all these inputs to arrive so you can experience them together. Otherwise, our daily experience would be a confusing hodgepodge of inputs in the wrong order—if you clapped your hands, you wouldn't see the clap, hear the noise, and feel your hands hitting each other at the same time.

David Eagleman, a neuroscientist at Stanford University, said that we don't experience the world in real time, we're always living a little bit in the past. That's because when we perceive anything, we collect sensory inputs from all over our bodies and the world, and not all of these inputs are processed at the same speed. Sound is processed faster than light. An input from your toes has to travel all the way up your spinal cord, while a signal from your nose doesn't have as far to go.

And he's right: According to a wide variety of studies, right now only lasts a few seconds or less. More intriguingly, it might not be right now at all, but right a-few-seconds-ago.

Right now is definitely not a whole year, it's not a day, and not an hour—these timescales are too long. Even one minute, if you really think about it, is too much. “We come closer and closer, and we end up in the few-seconds range,” he said. “Close to how long it would take if I say, ‘Now.’”

The experienced moment is a more conscious, psychological sense of now, "a slightly longer period in which a single event seems to unfold," as Burdick wrote. This experienced moment has been found repeatedly to be around 2 to 3 seconds. In a paper in PLOS One, researchers looked into this by showing people movie clips—a representation of the kinds of multi-sensory experiences we have in the real world. They scrambled the sequence of events within and beyond intervals of 2 to 3 seconds. They found that within 2 to 3 seconds, the brain was able to fix the order. But above that timescale, there was a dramatic increase in an inability to understand the clips.

The functional now we've touched on already. This is the very small time period in which your brain experiences sensory inputs at the same time. This is mostly unconscious—your brain waiting for the signal from your toe—and takes place in the milliseconds range.

Wittman explained that there are multiple "nows," comprising different layers of our experience. He outlined three: the functional now, the experienced moment, and mental presence.

But if our right now is so short, how can we be aware of things that last longer than that? We’re able to enjoy things that last longer than a few hundred milliseconds, like music, books, conversation, movies.

(Eagleman said in a lecture that it also means if something killed you very quickly, you would be dead before you even knew it. This could explain the mysterious last scene of [spoiler, if you still haven’t seen it] The Sopranos, in which the screen goes black while Tony eats with his family at a restaurant: A surprise, well-aimed bullet to the head would kill before now had a chance to catch up.)

It can also create some variety in _right now_s. If two people touch their nose and their toe at the same time, both will feel the touch simultaneously, Eagleman said. But for a taller person, the signal has further to travel than a short one, leading to the remarkable conclusion that “tall people may live further in the past than short people.”

But Wittman said that right now has to be able to do more, so that we can have an integrated whole experience. That's what he calls the third tier: mental presence. It's the right now rooted in the larger, narrative self, and it's built from the other, smaller nows. It's the functional nows and experienced nows linked together, with the help of our memories. This is how everything we see, hear, and feel seems to take place now and yet we also experience the fluid passage of time—our perception is, thankfully, not in static chunks of minute nowness, even as those blocks of right now lie at its core.

Wittman said we can also see evidence of this in other places—like a metronome. If you listen to a metronome tick, the ticks are all the same and not being grouped in any particular way. But we do hear a grouping: either one-two, one-two, or if it’s faster, one-two-three, one-two-three. “Although these chunks are not in the metronome,” Wittman said, “our brain creates these units of perception.” For images that can be visually interpreted in different ways, like the duck-rabbit or vase/faces "such changes in perceptual content occur spontaneously, at roughly 3-second intervals," observed one study on the present.

Two to 3 seconds for integration might be a “fundamental component of human cognition," the authors wrote, given that similar results have been seen across different tasks. It may "reflect a general organizing principle of human cognition—better defined as the ‘subjective present." Or in other words, “the phenomenal impression of ‘nowness.’”

In one of Eagleman's experiments, he told participants to push a button that caused a light to flash at the same time. Then, Eagleman inserted a small delay between the button and the light. Soon, people’s brains altered perception so that the light and button were simultaneous again. When Eagleman removed the delay, people’s brains still accounted for it: The next time a person pushed the button, they perceived the light as flashing before they pushed the button.

Our sense of right now—whichever one you mean—isn't passively measured and tracked and the brain, but constructed by it, Eagleman said. We can see that in his light experiment, or in other examples where this construction breaks down.

In a case study that Douglas Fox wrote about in the New Scientist, a man referred to as “BW” was driving when suddenly it was if he was speeding at an incredible pace. He tried to slow down, but the outside world continued to zip past him. BW felt like the outside world was going faster and faster, but actually he had slowed down. “He walked and talked in slow motion: when his doctor asked him to count 60 seconds in his head, he took 280 seconds to do it," Fox wrote. "It turned out that he had a tumor in his brain’s frontal cortex.”

In 2007, neurologist Oliver Sacks wrote about a man named Clive Wearing, whose hippocampus, a region of the brain critical for forming new memories, was damaged after he contracted viral encephalitis. Wearing existed only in the “now." If he was holding something in his hand, a chocolate for example—it would constantly present itself as brand new. As his wife described in her memoir, Forever Today:

“Look!” he said. “It’s new!” He couldn’t take his eyes off it.

“It’s the same chocolate,” I said gently.

“No . . . look! It’s changed. It wasn’t like that before . . .” He covered and uncovered the chocolate every couple of seconds, lifting and looking.

“Look! It’s different again! How do they do it?”

The way we experience now is for our survival. We need to understand when things in the outside world happen at the same time, in what order they happened, and be able to use our memories to create a narrative through time. “It was as if every waking moment was the first waking moment," she wrote. "Clive was under the constant impression that he had just emerged from unconsciousness because he had no evidence in his own mind of ever being awake before. . . . “I haven’t heard anything, seen anything, touched anything, smelled anything,” he would say. “It’s like being dead.”

Each theory of right now has one thing in common: It challenges the notion that the present is reliable and objective, or that it stretches out infinitely in front of us, even if we sometimes perceive it that way. This is an important reminder because the way we think about time affects the kinds of decisions we make.