What Happens at the Speed of Light - Speed of Light - Faster than Speed of Light
The Video explains what happens at the speed of light (relativistic speeds) and why mass increases with speed. You will know, the basics of Relativistic mass and the rest mass. The video explains how the Einstein's mass energy equivalence formula E= mc2 can be used to explain the change in mass of of the object at the speed of light.
The concept of time dilation and length contraction has also been covered here.
The Speed of light is the ultimate speed limit. Nothing in the universe can break this speed barrier. There is only one way to reach to this limit and that is, the particle has to be massless.
You should not think of the speed of light as something moving through space. The speed of light is very special.
As your speed becomes comparable to the speed of light, the time itself slows down due to time dilation, your mass increases and your length contracts due to length contraction.
But as soon as you reach exactly at the speed of light, the flow of time completely stops, your mass becomes infinite and your length in the direction of your travel becomes zero.
So if we could somehow reach to the speed of light, we would neither feel space nor time.
When the object is not moving with respect to an observer then it's mass is called the rest mass. It is also known as the invariant mass.
But the relativistic mass of the object depends on its velocity with respect to an observer. We also call it the moving mass.
Now the question arises after all, why the mass of the object increases when it moves?
And is the relativistic mass real or just an illusion? But first you need to know what actually the mass is?
Let me tell you that nothing in the universe that has mass, can travel at the speed of light. To travel at the speed of light the object or the particle must be massless. For example photons which are completely massless, travel at the speed of light.
Because as the particle would approach the speed of light, it would be heavier and heavier.
And at the speed of light, it's mass would be infinite, so it would need infinite energy to accelerate, which is practically not possible.
So any particle with nonzero mass cannot reach to the ultimate speed limit, the speed of light.
We know the Einstein's famous mass energy equivalence Formula-
E= mc^2.
Where E is Energy, m is mass and c is the speed of light in vacuum.
So what does it mean?
It actually means that mass and energy are not two different things. They are inter convertible.
But Why increase in mass is observed when any object approaches the speed of light?
We know that moving objects have energy associated with them, known as the kinetic energy. The kinetic energy increases with increase in the speed of the moving object.
Hence the total energy of an object is increased when it moves.
The moving particle having mass, not only has energy stored in it, in the form of it's mass but it also has immense energy associated with it, in the form of kinetic energy.
As by the mass energy equivalence formula, we know that mass and energy are actually the same thing and also interchangeable.
So we need to take into account this kinetic energy too.
So if any observer somehow measure your mass, you would seem much heavier in comparison to your rest mass.
But as soon as you come to rest your relativistic mass comes down to your rest mass.
So this is the reason why the mass of a moving object seems to increase.
Let's now understand it mathematically.
We will now see, how changes in mass, time and length are observed at relativistic speed.
M = m0/√(1-v2/c2)
Here M is relativistic mass of the moving object
m is rest mass
v is the velocity of the object
and c is the speed of light in vacuum (299,792,458 metres per second)
The factor 1/√(1-v2/c2) is called the Lorentz factor
So when speed of the object is negligible in comparison to the speed of light i.e. v is lesser lesser than c, Relativistic mass is same as that of the rest mass. But when the object achieves the speed of light i.e. v=c, the relativistic mass of the object becomes infinite.
But at speeds higher than the speed of light i.e. v is greater than c the mass becomes imaginary.
We know that the imaginary value of mass is not possible. So it is clear that it's not possible to achieve speeds higher than the speed of light.
In the same way you can analyze the following formula for time for three cases i.e. when v is lesser lesser than c, v=c and v is greater than c.
T = t0/√(1-v2/c2)
You will see when v is less than c but comparable to c, the time dilates or in other words when you reach near the speed of light, time passes slower for you. This is called time dilation.
Moving at relativistic speed not only affects mass and time but also the length.
If you move at speed which is close to the speed of light, your length will contract in the direction of your travel.
It is clear by the following formula.
L = l0√(1-v2/c2)
This phenomenon is called the length contraction.
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