Taken from the book “The ant and the Ferrari” written by Kevin Spackman:
You’ve probably seen the very popular TV series MythBusters, where Jamie and Adam test popular myths to decide if they are ‘Confirmed, Busted or Plausible’. It’s a fun and easy format to follow, so let’s use their approach to begin our investigation.
In typical MythBusters’ fashion we’ll start by blowing up a car. (They love their explosions!)
Like Jamie and Adam, we’ll replay the car explosion in ultra-slow motion. When we do we see thousands of fragments flying in all directions: a bit of a door going this way, a wheel going that way. But rather than just observing the overall carnage, we’re going to analyse what happens to each of these pieces, one at a time.
The best way to do this is to pause the video and follow each fragment as we advance the video frame by frame. Doing this allows us to calculate the speed and direction of motion of every individual piece using the following technique:
1. We determine the speed of each fragment by seeing how far it moves between successive frames. For example, a door might move 3 metres between two frames while a wheel might move 6 metres. If that happens the wheel must be going twice as fast because it has travelled twice as far as the door in the same time.
2. We determine the direction each object is moving in by drawing a line that joins its position as it moves from one frame to the next.
When we overlay these speeds and directions directly onto the video footage we notice something very interesting. No matter which frame we look at, the fragments furthest away from the car are going the fastest and the items closest to where the explosion began are going the slowest. But it’s even more precise than that. An object twice as far away is going twice as fast. An object 3.24 times as far away is going exactly 3.24 times as fast.
We also notice that each particle is moving in a direction pointing directly away from one single point. And what’s so special about that point? It’s exactly where the car used to be.
If we rewind our video and play it back in reverse we find all the fragments fly back together into a single place, at exactly the same time, to form a car. It’s like going back in time. But if any of the directions are misaligned, the objects won’t all meet back at the same place. Similarly, if some of the speeds are too fast those objects will arrive too early and carry on past the central point before the other fragments arrive. Again, we won’t get everything back together in one nice car.
The only way we can get everything back together in one piece is if:
- All objects move directly towards a single point. Their angles must be perfectly aligned.
- The speed of every object is perfectly matched with how far away it is from the central point.
- Items twice as far away must be going twice as fast. Items 2.41 times as far away must be going 2.41 times as fast. The match of speed and distance must be exact — otherwise they won’t arrive at the same time.
Now supposing we hadn’t seen the whole video of our car explosion, but were only given a single frame recorded halfway through the explosion. If all the speeds and directions of every fragment were marked on that frame, and they all perfectly matched our requirement of speed and direction, we could reasonably conclude all the fragments must have been in the same place at the same time in the past. That is, they came from a single explosion.
This brings us to a most surprising and unexpected discovery.
In the 1930s, astronomer Edwin Hubble decided to measure the speed of the stars and galaxies using the same technology the police use when they check your car’s speed with a radar gun. Hubble was gobsmacked to discover exactly the same pattern with the stars as we’ve just seen with our exploding car: stars that were twice as far away were going twice as fast and galaxies that were 127 times as far away were going 127 times as fast. This was a total shock to him, because at the time everyone expected all the stars to be fixed nicely in their own place in a static Universe.
Since then, thousands of people have checked literally billions of stars and galaxies using a variety of different speed-measuring techniques — and they always find the match of distance and speed is exact. We can be as confident of the stars’ speed as the police can be of your car’s speed. If we don’t doubt the police radar guns then we shouldn’t doubt the speed of the stars.
What was even more surprising was to find that all the stars were moving away from a single point, just as the fragments in our car explosion were. They’re all perfectly aligned. This can’t possibly be a coincidence. The only sensible conclusion we can come to is that at some time in the past everything in the Universe was squashed together in one place
We can easily calculate how long ago that was, by dividing the distances to each star by their speeds. It’s the same technique we use when calculating how long a journey is going to take. We divide the distance of the journey by how fast we’re going to drive. If it’s 300 km and we’re going to drive at an average of 60 km/h then it will take us 300/60 = 5 hours. When we do this calculation for the stars we find the entire Universe — every star and every galaxy — was squashed together into a single point 13.7 billion years ago.
It’s looking suspiciously like some sort of big explosion took place.