For a whole day, forget about the clock. Eat when you’re hungry and sleep when you’re tired. What do you think will happen?

You may be surprised to find that your day is much like most other days. You’ll get hungry when you normally(正常地)eat and tired when you normally sleep. Even though you don’t know what time it is, your body does.

These types of daily life are called circadian rhythms(生理节律), and they are more than just habits. Inside our bodies are several clocklike systems that follow a 24-hour cycle. Throughout the day and night, our inner clocks directly change in temperature, body chemicals, hunger, sleepiness and more.

Everyone’s rhythms are different, which is why you might like to stay up late while your sister always wants to go to bed early. But on the whole, everyone is programmed to feel tired at night and energetic during the day.

Learning about our body clocks may help scientists understand why problems arise when we act out of step with our circadian rhythms. For example, travelling across time zones(时区) can make people wake up in the middle of the night. Regularly staying up late can make kids do worse in tests.

“There is a growing sense that when we eat and when we sleep are important parts of how healthy we are,” says Steven Shea, director of the Sleep Disorders Program at Brigham and Women’s Hospital in Boston. One way to learn about how our body clocks work is to mess them up and see what happens. That’s what scientist Frank Scheer and his workmates did in a recent study.

Staying up night after night, their studies suggest, could make kids extra hungry and more likely to gain weight. And regularly sleeping too little, Scheer says, may be one cause of the recent increase in childhood obesity(肥胖症).

Do you want to know how someone is feeling? You can look at his or her face to find out. But there might be a better way: Close your eyes. Just listen.

Michael Kraus is a doctor. He did a study. The study shows that people should listen to voices. It is the best way to learn how people feel. The study says just listening is better than just watching someone speak. But it is also better than watching and listening at the same time! It might seem smart to listen to people and watch them at the same time. But Dr. Kraus says this can cause problems. “It might split your attention,” he says.

Dr. Kraus said something else, too. Sometimes, people's faces can hide their feelings. They might not want to show they are sad or mad. It is harder to hide your feelings with your voice. “That might be why listening is the best way to know how someone feels”, Dr. Kraus says. For the study,Dr. Kraus did a few tests. One test used 266 people. They were all strangers. They were put together in pairs to talk to each other. They talked about movies and TV. They also talked about food and drink. The strangers had these talks in two places, both in a room with the lights on and in a dark room. After alking, the people wrote down their own feelings and what they thought their partners felt. What Kraus found was a surprise. People were better at knowing their partner's feelings when the lights were off. Another professor Boris Paskhover did some research and concluded the same results.

Sophie Scott is a communication expert. She works at a university in England. Ms. Scott said the study is interesting. But she does not think it is perfect. Ms. Scott said that other studies have shown other things. Their results were different. Ray Wilkinson is a teacher. He teaches about communication. Mr. Wilkinson’s studies show that people use their bodies to show how they are feeling, too. They might change their face or body movements. They can do this to make a point. Mr.Wilkinson said that sometimes, your words and face do not match. They might send different messages. But that might not be a mistake. Sometimes, people do this on purpose. It can be part of what we are trying to share.

“You expect your friends to see you in a positive manner, but they also are observers of the personalities that could cause you an early death,” said Joshua Jackson, an assistant professor of psychology in Arts & Sciences.

Published in the journal Psychological Science, the study shows that your personality at an early age can predict how long you will live across 75 years and that close friends are usually better than you at recognizing these traits. “Our study shows that people are able to observe and evaluate（评价）a friend’s personality exactly enough to predict early death years down the road,” Jackson said. “It suggests that people are able to see important characteristics related to health even when their   friends were, for the most part, healthy and many years from death.”

While other studies have shown that a person’s view of his or her own personality can be   helpful in evaluating death risks, there has been little research on whether a close friend’s personality evaluation might also predict the chances of a long life.

To explore this question, Jackson and colleagues analyzed data（数据）from a longitudinal study that in the 1930s began following a group of young people in their mid-20s. The study included wide-ranging data on participant（参与者）personalities, both self-reported and as reported by close friends.

Using information from follow-up studies and searches of death certificates（ 证 书 ）, Jackson and colleagues were able to record dates of death for all but a few study participants. Peer（同龄人）evaluations of personality were stronger predictors of death risks than were self-evaluations of personality.

“There are two possible reasons for the advantage of peer evaluations over self- evaluations,” Jackson said. “First, friends may see something that you miss; they may have some insight that you do not. Second, because people have several friends, we are able to average the characteristics of any one friend to get a more trustworthy evaluation of personality. With self-reports, people may miss certain sides of themselves and we are not able to counteract（抵抗）that because there is only one you, only one self-report.”

The study also shows some gender differences in self-evaluation: Men’s self-evaluations of personality were somewhat useful in predicting their lifespans（寿命）, whereas the self-reports of women had little predictive value.

“This is one of the longest studies in psychology,” Jackson said. “It shows how important personality is in influencing important life outcomes like health, and that information from friends can play a critical role in understanding a person’s health issues.