杏吧原创

Is time a real phenomenon or a human perception?

cathal76

Time is real! That鈥檚 my position, anyway.

More specifically, time isn鈥檛 real in the same way that a basketball is 鈥渞eal鈥� 鈥� it鈥檚 not something you can poke at or hold in your hands. Instead, we should say that time 鈥� like space and quarks 鈥� is 鈥渞eal鈥� if it is a useful concept in our best understanding of how the universe works. And that鈥檚 certainly true. In every theory that we have 鈥� Newtonian mechanics, relativity and quantum mechanics 鈥� time plays a central role. That鈥檚 not to say a better theory won鈥檛 come along where time isn鈥檛 fundamental, but even then, that theory will have to show how time emerges to play such an important role in how we perceive the world.

Is time digital or analogue?

Kingsley

The short answer is we鈥檙e not sure. The slightly longer answer would add 鈥溾�� but it鈥檚 probably analogue鈥�.

Time is certainly analogue (continuous and smooth) according to the measurements we can do with present-day technology. Quantum mechanics and general relativity both feature a perfectly continuous notion of time. However, it鈥檚 possible that an eventual reconciliation of the two will result in time becoming digital.

If we started to fall into a black hole, would we notice that time was moving more slowly?

Mark B

The issue here is one of human perception, not of physics. We perceive time to move because we come equipped with clocks in our bodies 鈥� our heartbeat, breathing and pulses in the central nervous system. We would only ever perceive time to slow down or speed up if those biological clocks became out of sync with mechanical clocks. But a physical phenomenon like falling into a black hole affects all types of clocks in the same way. So rather than thinking of time as speeding up or slowing down, it鈥檚 better to compare the amount of time elapsed on different clocks that travel through different paths in space-time.

Does time exist in an empty universe?

Richard Kenno

The simple answer is yes, time would exist, just as space does. It would be governed by relativity.

However, the arrow of time 鈥� the flow of entropy that determines which direction is the past and which is the future 鈥� would not exist in a truly empty universe.