Time is a sweet yet strange thing. It’s invisible, yet its passage can be seen and felt. Some people have too much time on their hands, but it can easily slip through your fingers and you may find that you never have enough. Although time can be measured very accurately our perception of time can vary dramatically; Einstein has been quoted as saying:
“When a man sits with a pretty girl for an hour, it seems like a minute. But let him sit on a hot stove for a minute and it’s longer than any hour. That’s relativity.”
Not that we need any further clarification, but we all know that an hour in the office drags by interminably whereas a day spent with your children whizzes by in next to no time. And with a nod to quantum mechanics, the kettle takes forever to boil – if you watch it.
So is time just an illusion, or something more tangible?
The importance of time
Time is intrinsically linked with space and is often described as the 4th dimension. Some may argue that time itself is not just a single dimension in a single ‘direction’, but could be multidimensional, so instead of a time line of past, present and future, we could have an area of time, a volume of time, or perhaps something even more complex. But what does this mean for us in real terms?
If time is a (multi)dimension, can we travel through it, just as we can through space? Or do we remain stationary but time flows on around us?
Einstein proposed that the dimensions of time and space are so heavily connected that they can be collectively referred to as “spacetime”. Already this gives a glimmer of hope for time travel – travelling through time as if it were space. But if space and time are intertwined, how can we be sure of what space and time as separate entities really are? We are already familiar with the spatial dimension and travelling through it – we have parameters to describe this: speed (spatial distance travelled per unit time), velocity (spatial distance travelled in a given direction per unit time) and these show one of the relationships between time and space. But time appears to be more ethereal…so what do we mean by time travel?