If I Threw a Galaxy Sized Frisbee

Last night I watched a documentary on BBC4 about mapping the universe. It was an interesting programme and reminded me of a conversation I had with a Japanese friend before Christmas about astrophysics. All I can say is a lot has changed since my Astronomy GCSE in 1997. Afterwards, I decided to write down a few thoughts on why the universe is expanding at a faster and faster rate rather than slowing down. Let’s start with a little thought experiment.

Have you ever thrown a frisbee? You’ll note, even if you get a good flat angle on the throw, the frisbee will eventually fall to the ground. It may glide on for a while or crash quickly. It may stretch off in distance in a straight line, veer off to the side, or go high but short. Regardless of the specifics, it will hit the ground.

The frisbee’s energy comes exclusively from your throw and is then dependent on its own aerodynamics, the atmosphere and environment around it such as rain or wind, and finally on our planet’s gravity. Ultimately, there is no fighting gravity without your own thrust and especially without enough to put the equation in your favour.

Without Gravity
One question to ask may be, if there was no downward gravitational pull, would the frisbee fly further before stopping? It would stop rather than drop because there would be no gravity to pull it to earth. This new stopping point would be the point at which it ran out of energy from the initial throw. If that point is beyond where it fell with an identical throw with gravity, then gravity brings the frisbee down when its energy dips below a certain level. If they are the same, then there’s no pull on the frisbee until it’s out of energy. As frisbees do not just drop to the ground, but get successively lower until they hit it, we know there’s a threshold whereby gravity beats energy or diminishes it.

A Single Gravitational Point
Now let’s imagine that gravity is present again, but this time the source of gravity is the thrower and there’s no other gravity around. Eventually, when gravitational pull is stronger than the energy throwing the frisbee away, it will come back into the thrower’s hands.
In theory, gravity diminishes the further away from the centre an object goes. So the further the frisbee flies, the less power gravity exerts over it and the less energy is required to keep moving away. In theory therefore, if the frisbee’s energy is constant it will eventually get to a point where the thrower no longer has a gravitational effect on the frisbee and it is only subject to its own mass. In such a circumstance if it were to run out of momentum, it would stand still or drift.

The Frisbee Equation
You could therefore designate a value to the amount of effect the thrower’s gravitational pull has on the frisbee. The Frisbee’s speed could therefore be given a value such as X, which is the speed the frisbee would fly if there was nothing holding it back. The drag effect on the frisbee due to the thrower’s mass would be Y. The true speed of the thrown frisbee would therefore be X-Y. However, Y would not be constant, but would be based on distance. It would therefore be of smaller and smaller value the further from the thrower the Frisbee gets. This would require a distance to effect ratio which is beyond my mathematical skills.

The Constant Frisbee
Now if we imagine the frisbee is the source of its own energy, so instead of being thrown, it takes off much like a rocket from the thrower. Let’s also say that this energy is constant. It will always, in a vacuum, have the speed of X. The single variation in the experiment will be gravitational effect (Y). As it leaves the hand, the value of Y will be at its strongest and will therefore diminish X significantly, but X is enough to pull away from the hand even when Y is strongest. The frisbee will continue to pull away, but as Y slowly diminishes, it will get closer and closer to it’s natural speed, X. This is the vital thing, in doing so, the frisbee will appear to speed up as it goes further away from the thrower. Once Y=0, the frisbee will go at X speed and will maintain this speed so long as its energy continues. With nothing to drag it back, it will continue at a constant forever.

Where the Map of the Universe Comes In
In 1997, I sat a GCSE in Astronomy at Cirencester College, a suggestion for a fun side course by our Physics and Chemistry A-Level teacher. At that time, it was thought that the expansion of the universe was slowing down. In fact, that at some point, we would be dragged back to the centre of the universe in the Big Crunch, the opposite of the Big Bang. This would be like a reverse bungee jump in a way – you might call it a bungee rocket. In a normal bungee jump we jump downwards until the rope goes taught and we spring back a little, but gravity keeps us down there. In a bungee rocket, gravity has a rope, so when the rocket fires away its thrust powers it up for a while, but then the rope goes taught and gravity pulls the rocket back to the ground.

Saul Perlmutter, Nobel Laureate 2011 for Physics, in his office.

Where Frisbee Equation and Universe Expansion Collide
However, Saul Perlmutter and his team, who set out to measure the slowdown in the universe’s expansion, instead discovered it was speeding up. The question for them is why might this be? Some theories previously had looked at the gaps between stars and universes and concluded the existence of dark matter. Experiments have suggested pockets of dark matter does exist and they do have a gravitational effect.
However, it is also suggested these pockets are finite in total mass, so as the universe expands, much like stretching dough, it gets thinner and thinner. The Astrophysicist on the BBC4 documentary suggested that dark matter’s thinning is replaced by dark energy – an unknown and unquantifiable random source of energy which is powering expansion.
However, it makes more sense to think of each galaxy as a frisbee with its own seemingly constant source of energy generated by its rotations (and own gravity) which is pushing it away from the big bang. The reason the universe is expanding is because the effect of Y from the centre of the big bang, from dark matter, and from other galaxies is diminishing, allowing each galaxy to get closer to its X value. When Y gets to 0, we will see, if we’re still alive as a species then, whether our galaxy has constant energy or if it too will run out of energy.
If we were timeless Gods, it would be interesting to see if the galaxies run out of momentum before Y gets to 0 or not. If they do, they could be dragged back to the centre as momentum reverses or if not, then they would drift in space.

Note: This is just speculation and logic on my part, and I’m interested in serious rebuttals with either logic or scientific facts.

Leave a Reply

Your email address will not be published. Required fields are marked *