As some of you know, my background is in physics and astronomy. (Don’t tell me your ‘star sign’ as a smack in the mouth often hurts…!!!)
I apply my physics training to lasers and IPLs and stuff, but I don’t really use my astronomy education much, these days. I like to ‘keep up’ by reading New Scientist and various online blogs and science sites.
But something I see regularly is the topic of time travel. This is something which fascinates most people, for one reason or another. Many people would like to go back in time and change something. Some want to go into the future and see how things pan out.
So, the question is, is time travel really a possibility? Well, here’s my tuppence worth.
My answer is no. And yes!
No, in that travelling backwards or forwards in time to some point in the past or future, is not possible, in the way most people imagine. That is simply because most people don’t understand how the concept of ‘spacetime’ works.
Spacetime was ‘devised’ by Albert Einstein to describe the universe around us. He surmised that we live in a three spatially dimensional universe, with a time dimension, moving only forwards. (Although, interestingly , there is nothing in physics which prevent moving backwards in time, except, perhaps entropy…)
So, according to Einstein, everything in our universe exists in a four-dimensional spacetime. We cannot move through space without also moving through time.
And vice versa!! This is the critical point here, we cannot move through time without also moving through space. If you wanted to go back in time, let’s say by 100 years, then you must also move through the relevant space too, to reach that particular point in spacetime.
Even if you only wanted to go back five minutes in time, you’d need to move through space to the relevant place.
So, if you were to build a time machine, it would have to be able to move you through both space and time, to the point you’re trying to reach. Which is tricky, to say the least.
Also, can you be sure that the point you’re aiming for is actually “there”? This raises a very serious issue. All time travel notions have one basic assumption – that your ‘destination’ exists! Somewhere. And sometime!!
I find this quite disturbing since it means that ALL of spacetime must exist, for ALL time. As a physicist I consider this to be too bizarre. Why should all of spacetime, for all space and all time, exist, for all of time?
It’s simply ludicrous. I can’t accept that idea.
So that’s the ‘NO’ argument. What is the ‘YES’ argument?
That’s simple. We are all time travellers. Each day we travel through time, and space, at the rate of one second per second, one hour per hour and one day per day.
Forwards, never back.
I’m quite happy with that scenario. It seems to work well. Let’s keep the time travel stuff in science fiction.
CAVEAT
After I wrote the above, I thought about a method of ‘time travel’ that does actually exist. Einstein’s equations showed that time dilation can occur due to high velocities (from Einstein’s ‘Special Relativity’) or gravitational fields (from his ‘General Relativity’). Basically, time ‘appears’ to slow down as matter moves very rapidly, or as it approaches a strong gravitational field – relative to an outside observer.
This has been proven many times using atomic clocks. Our mobile phones would not operate properly if gravitational time dilation was not accounted for. This is due to the GPS satellites being so far from the Earth, where time runs a tiny bit faster compared with the Earth’s surface.
In fact, due to gravitational time dilation, time runs at different ‘rates’ across the entire universe. I tend to think of it like a river – time flows freely when far from massive bodies like stars, galaxies or black holes. But it slows down near those objects. A bit like a river’s flow near a bank, or near its middle.
I think Matt Smith once described time as ‘wibbly, wobbly’ (in his Dr Who persona). I thought that was actually quite a good description.
Anyway, time for a wee dram…
Mike.
Mike Murphy's Blog 