Hey y’all. Been a long time, isn’t it? Well, can’t say I was busy, but I wasn’t free either. My Final Exams are going on, and many things happened in my life too. So yeah, I had time, but didn’t feel like writing. I’m truly sorry for not posting these months. I truly am. Without further ado, we’ll jump into the topic.
Electromagnetic Waves
I was stu”dying” for my final exams, and came across the term “Radiation Pressure” in Physics. I was studying about the Electromagnetic Waves, their nature and all those stuffs. An interesting thing that I found while doing so, was, these Electromagnetic Waves have a particular Momentum.
Momentum
The quantity of motion of a moving body, measured as a product of its mass and velocity.
Usually, in Newtonian Physics(studying the physics of everyday objects), momentum is said to be the product of mass and velocity of a body. but when it comes to Quantum Physics(studying the physics of microscopic objects), there was a modification done here. You see, an object to have momentum, it needs mass. But Electromagnetic Waves, are purely, the propagation of Electric Field and Magnetic field in space, perpendicular and regenerative to each other. In simple terms, they have no mass. So how come they produce momentum?
This question is answered simply by one word, “Energy”. Yes, though these Waves don’t have mass, they carry energy. And this energy is used to create the required momentum.
So then, why the heck did I use the word “Light” here? It is because, Light too, is an Electromagnetic Wave. It was proved when the speed of light (3 x 108 m/s) matched to the speed to regular Electromagnetic Waves like Radio Waves, Infra-red rays and Ultraviolet Waves.
I read that, an equation defines the momentum, for Electromagnetic Waves. The equation is given by, p = U/c. Here p is the momentum and U is the Energy the Electromagnetic wave carries, and c is the speed of light. So with 2 values here, we can find the rest. Anyways, the thing is, momentum is determined solely by the Energy of the Electromagnetic Wave, since c is constant.
So here, what happens to the energy? These energy actually comes from the source of these waves. This energy usually dissipates into another form of Energy, when making contact with any other entity. The best example I can give is, the Sun itself. Yes, sunlight’s energy is converted to heat, when met with everyday objects.
A natural question arises here. So, if the Sunlight carries energy, there should be a momentum for the sunlight too right?. So, then, why isn’t anything moving, when the sunlight strikes? Well, to put it in simple words, the value of c is quite large (approx 300,000,000 m/s), and mathematically, if the denominator is large in a fraction, the value starts to decrease. And that’s what’s happening here.
The energy carried by the sunlight is way more less than c, and when it is further more divided by c, the value becomes quite small. And since the value becomes smaller, such small momentum, can never move macroscopic everyday objects.
Possible in Reality?
Well, you may ask, that, if Light is never gonna move anything, then how the hell can it move a spaceship. Well, as said earlier, the value of c is quite large, so the momentum is less. But what if we find a way, to keep the energy to a high value, and slow down the speed of the Electromagnetic Wave(Light)? In simple words, we increase the numerator and decrease the denominator, so the value starts to increase in magnitude.
So, as the momentum increases, automatically, by Newton’s third law, if the objects has the correct mass and velocity, when collided with an Electromagnetic wave, the object starts to more. Due to many reasons such as Gravity and Air Resistance, it is difficult to see an object move because of Light, here on Earth.
But in space, it is possible to move an object as there is vacuum. So how can we increase the Energy? Well, we can increase the Energy at the source, at a high frequency, and the energy problem is solved. Now the real problem is the speed. We can decrease the speed by using multiple reflections and refractions. But the catch is, it’ll effectively affect Energy too.
The Energy too, starts to decrease and we are back to square one. Energy is less, and the value of c is still many times greater. So this is the real problem to solve. We can try to use different materials, maybe to use a light weight fabric, and beam a light on it. Maybe it’ll move.
And another problem is Conservation of Energy. If we connect both the transmitter and the object (light weight fabric), by any means of contact force, there will no motion here. This is because the net energy of this entity is 0. It’s like trying to push your own body with your hand. You won’t move right? Exactly, that is what’s happening here too.
End Note
Anyways, I surfed through the internet and found that this idea was theorized in 1980 itself and yeah, there are some successful projects too. This is given by the name “Solar Sail”. Pretty cool right? Well, to know more interesting stuffs like these, do subscribe to this blog. Leave your comments below, and share to people who love these kinda stuffs. See you in the next post! Have a good one!
SpacesTrek 