Where’s my Lightsabre?

With the eagerly anticipated next instalment of the Star Wars saga breaking all the records, I thought I would kick off this brand new science blog with something topical. As a physicist, a lot of my ‘civilian’ (non-scientist) friends ask me when I will invent something that changes the world. “Where’s my teleporter?” they cry. “When will you invent time travel?” But probably the most common is “Why don’t I have a lightsabre yet?”

Well, what I’m about to say might just blow your mind. Because the truth is, you already do.

Yes, really.

Ok, well, kind of really. Bear with me and I’ll explain. But fair warning, this is going to get serious. My hope is that, by the end of this post, you’ll have learned something truly incredible, and understood it at a level you wouldn’t have thought possible. Because we’re all geniuses really, it’s just that some of us don’t know it yet. On with science!

This is you.


And this is a very tall building.


And this is the ground.


To begin with, we’ll start at the ground and get up to the top of the building. I know you want to take the lift, but let’s take the stairs instead.


It’s tough going right? It’s difficult because you’re working against gravity. But all that effort you’re putting in isn’t going nowhere. You’re storing up energy in the form of gravitational potential energy. It sounds technical, but it’s pretty simple. It’s just like charging a battery. When you charge a battery, electricity from the mains gets stored as potential energy in the battery, to be released later when you need it. When you climb the stairs, all that energy you put in climbing is stored inside you and it’s released again when you go back down. That’s why going up is so hard, but you can gallop down stairs without breaking a sweat.

Ok, so we’ve got to the top. Let’s use that stored energy to get back down to the ground again… No, no, the easy way!


So, what’s happening to you right now? First off, you’re falling, gravity is pulling you back down to earth, and as you fall, you fall faster and faster as you release all your gravitational potential energy and turn that into speed! It’s fun, the wind rushing through your hair (assuming you have any), the incredible view getting closer… and closer… and closer.


Well, nothing good lasts forever and, eventually, you have to hit the ground. And what happens then? Yup, you stop. Fast. But why? Because the ground is hard sure, but there’s more to it than that. If the force of gravity pulled you down, there must be some other force that pushed back on you to make you stop. Confused? Well, just turn the whole thing on its side. If you say, give a shopping trolley a good hard shove towards someone, then to stop it, they have to push back on it with the same force from the other direction.


But look back up to the top of the building. You fell a very long way, gaining a lot of speed, but you stopped almost immediately upon hitting the ground. Whatever this mysterious force is, it’s got to be pretty strong stuff. Far stronger than gravity! This force is, believe it or not, electromagnetism, and it’s the same thing that causes your bulbs to glow.

Here’s where things get a little more complicated. And, as is so often true in science, to find the answers to the biggest questions, we must go to the smallest of places.

This is an atom.


Everything you see is made up of these. In the middle of the atom is the nucleus, this has a positive charge, and orbiting around this, like planets round the sun, are electrons and these have a negative charge. Let’s give it a friend.


When you try and draw two atoms close to each other, the negative charge from the electrons on the first atom repel the negative charge from the electrons on the second. This is just like a magnet, with a north and a south pole. When you try to push two north poles towards each other, the magnets push away. It is actually exactly the same type of force that repels electrons away from each other. Let’s take a closer look at what is happening when this force occurs.

We’re almost there, so it’s time to get things serious. This funny little stick figure is known as a Feynman diagram.


People will tell you it’s complicated, but it’s not. First off, we’ll turn it into pictures…


…there. So, we have our atoms moving towards each other, just like before, but it’s just the electrons we care about. That’s what the straight arrows on the Feynman diagram represent – the electrons moving towards each other. Now, when they meet, they’ll start to push away from each other, but for that to happen, energy must be exchanged from one to the other. Again, it’s like you pushing the shopping trolley. You need to give it some of your energy to make it move away from you, which is why after playing shove the shopping trolley around for a few hours, you get tired and need to sit down.

So, how does one electron give some energy to the other? I’m going to write this bit large because this is the important part. LIGHT! When the electrons get close enough to each other, there is a tiny flash of light that comes from one electron and is absorbed by the other. This is the wiggly line on the Feynman diagram. And that’s what happens whenever any solid object touches any other. When you push your shopping trolley (you really like that game, huh?) the electrons in the atoms of your hand get close to the electrons in the atoms in the trolley and there is a flash of light and the trolley is pushed away.

But! I hear you cry. But! I don’t see any flashes of light when I touch things! Well, that’s because all the light that is emitted by your hand is absorbed by whatever you’re touching. It doesn’t go in all directions. It’s like a fibre optic, with a bulb at one end, inside a box, and the other end put inside an empty box. If you close the lid on both boxes, you can’t see the bulb emitting the light, or the light coming out of the fibre optic at the other end. There is light going from the bulb to the end of the fibre, but you can’t see any of it.



So, when you push your trolley, an INVISIBLE FLASH OF LIGHT pushes the trolley away. When you hit the ground, a very intense but still invisible flash of light stops you dead (if you’ll pardon the pun!) and when a sabre cuts into your flesh, it is light that causes it to cut you, coming from the blade and being absorbed by your body to push your atoms apart and sever your vital bits and things.

And there you have it. The only difference between a lightsabre and a normal sabre is the lightsabre has cut out the middle man and delivers the light directly. Also, it looks a lot cooler.

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