Long-time readers may note that this blog bounces (veers?) between space-related content and time/temporal physics-related content. Today, aside from admitting that (not surprisingly) the two topics are primary passions of mine, I’ll tell you why they’re related, and intimately so.
It’s all Einstein’s fault.
Put very simply, according to Relativity: When dealing with events in the universe, it is impossible to separate the distance of space from the passage of time.
This is why astrophysicists and cosmologists speak of actions in the universe occurring and affecting “space-time.” (Hence the “space-time continuum” that makes such a frequent appearance in sci-fi technobabble.)
What does this mean for us? Well, in day-to-day experience, not much more than the odd reality that the moon we see is 1 second old. Similarly, the sun we see is lagging 8 minutes behind us in time.
Why? Well, it takes the light that bounces off of the surface of the Moon 1 second to cross the 230,000-mile distance between the Earth and Moon to strike the retina of your eye, and it takes 8 minutes for the light that leaves the sun to cross the 93-million mile orbital void to get to Earth and reach your eye. As a result, we see the Moon and Sun as they appeared when the light left them, not when the light reaches us.
The same can be said of distant stars. The farther away a star is, the older it is. (Even if it’s 200,000 light years away – then you’re seeing it the way it looked 200,000 years ago.)
So, quizzically, yes – this means that universe we see is actually a horrible garble of apparent objects from intermixed times. Fortunately for us, compared to the incredible speed of light, we’re close enough (distance) to everything we need to experience, (e.g., our limbs, food, loved ones, walls, etc.,) so that this time lag is unnoticeable.
But when we start peering out into the rest of the cosmos, this distortion really matters. Many of the stars we’re studying may have already exploded… but if they exploded a few years ago, we won’t know it until light from the explosion reaches us, which could take millions of years if the star is far away.
Now, let’s take our time-distance thought exercises a step farther and ask what happens if we score the holy grail of the Search for Extraterrestrial Intelligence. What if, for the sake of argument, we receive and translate a friendly message from an incredibly advanced race of aliens? And what if, by fortuitous happenstance, they (hoping to aid other, younger life-forms) offer unlimited knowledge to any beings that can meet them on their world, face-to-face? Well, the offer doesn’t do us more than a hill of beans of good if it takes us 200 years for a multi-generational craft to get there, only to find that the benevolent race has gone extinct due to a problem with their parent star. We want to reach them as soon as we translate the message.
We want to separate the distance of space from the passage of time.
So, if we can conceptually and technologically conquer time travel, we will have in essence conquered space travel. If one can manipulate the passage of time, then the time taken to cross the distance of space with any type of propulsion system becomes an almost trivial tally – little more significant than the miles-per-gallon of a modern automobile.
Conventional propulsion systems will get us around in space for the foreseeable future, and more exotic systems will likely take us to the nearest stars. However, I believe it will be the mastery of time that will transform our race from provincial planet-hoppers to truly savvy, galaxy-trotting, cosmic-colonial game-changers.
Something to think about.