I’ve been fascinated with the concept of traveling to far-off suns and planets for as long as I can remember. I’d love to have a faster-than-light spaceship like the Millennium Facon or—given a choice—a time-and-space vessel like Doctor Who’s TARDIS.
Failing options like these, we are reduced to sub-light-speed travel, like generation starships that run at a small fraction of light speed and take hundreds of years to reach even the nearest stars to our own.
Of course, we all know what can go wrong here, with classic examples presented in Orphans of the Sky by Robert Heinlein, Captive Universe by Harry Harrison, and Non-Stop (a.k.a. Starship) by Brian W Aldiss.
Even if we were to come up with a technology that allowed us to build a spaceship that approached the speed of light, we would run into issues with general relativity and time dilation as found in Time for the Stars by Robert Heinlein. This is one of my favorite tales. Telepathic twin teenage brothers Tom and Pat are recruited for a special mission to discover other habitable planets. Pat stays at home while Tom heads out on a starship that approaches 99% of the speed of light. Since they are telepathic (which we learn is instantaneous / faster than light), Tom reports everything he sees to Pat. When Tom eventually returns home, he’s still a young man. By comparison, Pat is old and frail.
This reminds me of the classic Queen song ’39 from A Night at the Opera. This was written by lead guitarist Brian May, who had a BSc in Physics from Imperial College and has since gained a Ph.D. in astrophysics from the same institution. It’s a haunting song about a group of folks who head out searching for another planet to colonize. Sadly, due to general time dilation, they return to an Earth they no longer know.
The reason for my waffling about all this here is that I just started reading The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory by Brian Green. I can’t believe he wrote this more than 25 years ago. Where does the time go (no pun intended)? And why has it taken me so long to get around to reading it?
I’m still only at the beginning. I just finished page 52. But my brain has already been boggled. For example, in the case of Pat and Tom described earlier, I knew that one of the twins would perceive time as going slower for his brother, but I had no idea that BOTH brothers would perceive time as going slower for each other (I’m still trying to wrap my brain around this one).
Also, I was blown away when Brian explained the concept that we’re all traveling at the speed of light (but that’s not in the way we usually think about motion through space). Here’s my current understanding of what Brian is saying (although I may have got it completely wrong):
This idea arises from the way spacetime is described in relativity, where time and space are intertwined into a single entity we call “spacetime.” According to this theory: (a) We can think of the "speed" at which we move through spacetime as being constant for all observers and (b) in the three spatial dimensions (x, y, and z), we move at speeds much less than the speed of light. But in the fourth dimension, time, we are always moving forward at a rate of 1 second per second.
In the context of spacetime, the sum of our speed through space and time is constrained, and the "spacetime interval," which combines both space and time, remains invariant, meaning the total "motion" through spacetime for any object, including ourselves, is always at the speed of light.
More formally, in special relativity, this relationship is expressed with the equation:
(space speed)2 + (time speed)2 = c2
Where ‘c’ is the speed of light. Since we're always moving forward in time, the speed with which we "move" through space must adjust accordingly to keep the total "speed" consistent with the speed of light.
For everyday situations, we move very little through space compared to our constant "motion" through time. Hence, you could say we are "traveling through time at the speed of light." Based on this, I think the title of this column hit the nail on the head—traveling at the speed of light is possible and I'm doing it myself as we speak (I bet my dear old mum will be surprised)!
I can’t help myself, now I’m thinking of the "I’m traveling at the speed of light” lyric from the Queen song Don’t Stop Me Now, which was written by Freddie Mercury.
The scary thing is that all the above was sparked by what I’ve read in The Elegant Universe so far, and I’ve only just finished Chapter 2. Goodness only knows what cogitations and ruminations Chapter 3 will bring.
While we’re waiting for me to read and report further, do you have any thoughts you’d care to share on anything you’ve read here?
Travelling beyond the speed of light happens all the time. Have you seen pictures of the blue glow around fuel rods stored in water for a nuclear reactor? That is Cherenkov radiation, which happens when a charged particle, such as an electron, passes through a medium (such as water) at a speed greater than the speed of light in that medium.
I have to admit that I don’t understand all that I know about this.
I wish I could go forward 100 years to see how much more we understand about all this stuff by then.
In the equation, what is the definition of “time speed”? The equation assumes that “time speed” has units of distance/time. Along what axis is this distance measured?
Ah — you ask a tricky question — I think the general idea is that we are already traveling through time at the speed of light (which would explain why I’m always so tired). So this would be traveling along the time axis — all you have to do is stand still and do nothing in the other three dimensions, which works well for me because doing nothing is one of the things I do best 🙂
In the equation, “time speed” has the units distance/time. Along what axis is this distance measured?