Many factors can make time seem to speed up or slow down, researchers are finding, even whether a person feels accepted or rejected by others.

LONDON — Time, arguably our most precious nonrenewable resource, has a slippery nature in our minds. Sometimes it flows quickly. In other situations, it trickles at an unbearably slow pace. And, to the horror of many, it speeds as we age.

Why should something as reliable as a ticking clock be perceived with such inconsistency? Claudia Hammond, science author and broadcaster, explores this question in her new book, "Time Warped" (Canongate Books Ltd, 2012), out today (May 3).

She presented some of her findings at the British Psychology Society Annual Conference here in April, where she won the Society's Public Engagement and Media Award.

The present

Humans are remarkably good at measuring time in general. That is, when asked to estimate the length of, say, an hour, minute or second, we tend to be accurate, although scientists have yet to find a neuronal clock helping us with these measurements, Hammond said.

But our estimates can be greatly affected by psychological factors, including emotion.

In one experiment noted by Hammond, researchers asked people to mill about a room and socialize before telling the researchers, in confidence, which person they'd like as a partner in a subsequent task. Each participant was then individually taken behind closed doors and told one of two things: "We are sorry, but no one wants to be your partner; can you please work on your own?" or "Everyone chose you and now the only way to be fair is to have you work solo." The participants were then asked to estimate how much time they spent on the given task.

If the subjects thought popularity caused their seclusion, time seemed to pass very quickly. But for those who felt rejected, time stretched on and on. [Top 10 Mysteries of the Mind]

Attention and memory also have powerful effects on time perception, Hammond said. For instance, novel experiences, because they require more mental processing, seem to last longer than familiar situations.

"This is why walking somewhere new seems to take longer than the walk back," she said.

The past

"We are always assessing time both during and retrospectively," Hammond said. "When there is a mismatch is when time seems to have warped."

For example, time may move slowly during a bout of the flu — in part, perhaps, because fevers skew time perception, making minutes stretch out like hours.

But the time spent sick seems "weirdly quick in retrospect," Hammond said, explaining that the monotony is likely coded in the brain as one single experience, while an equal amount of time spent on, say, an overnight hike would result in many different memories. The camping adventure may pass by quickly in the moment, but will seem to occupy loads of time in retrospect.

Age also affects perception of the past, making last year's holiday season feel as if it happened last week. Often this feeling is blamed on the "proportionality effect:" A year is a fifth of your life when you are 5 years old, so it seems a long time, but at 50, a year represents a much smaller proportion (one-50th) and seems to take a corresponding amount of time. [7 Ways the Mind and Body Change With Age]

But according to Hammond, the proportionality effect is only culpable in part. As people get older, and accumulate experiences, fewer activities remain novel. As it gets easier, and less noteworthy, to complete a report or make a soufflé, time, in retrospect, speeds up.

If this is concerning, Hammond recommends seeking out new activities — especially on the weekends when time, for most, seems to especially fly. (Hammond admitted, however, she personally prefers to rest on the weekends, even if it makes time go by faster.)

The future

"The future is the mind's default," Hammond said. "When at rest and not having to do other things, it goes into the future."

In most people's minds, she said, the future is a spacious place where there are oodles of time and time-management skills prevail. Ask a busy person for 10 minutes today, and they won't have it. But ask for an hour sometime next year, and they will gladly schedule you in, even if they are unlikely to slow down in the interim.

And when scheduling events in the future, be careful with the wording, Hammond warned. Using a Wednesday meeting as illustration, she explained, if it gets "moved forward" by two days, people may turn up for it at both the beginning and end of the work week.

This is because people have different ways of conceptualizing time. Some think of time as something moving toward them, while others picture themselves moving into time, she said. The former type of person will think the meeting has been moved to Monday and the latter will think the meeting has been moved to Friday.

Overall, Hammond stressed, even though it is the most used noun in the English language, "time" is not as straightforward as we like to think.