Ever since Einstein’s
general relativity got recognized in the physics field, it changed the viewpoint
of gravity and invented a lot of new ideas for the upcoming theories. The
sensational principle of how mass bents the space-time and cause the ripple and
forms gravity is a unique yet incomplete theory for many generations.
UNDERSTANDING GENERAL RELATIVITY:
According to Newton, space and time are absolute and they
are not related to each other. He thought a mystic force(gravity) acts at the
center of the body and attracts others who are near it. This theory was widely
accepted at that time and also even in today’s generation we are still hung up
on that theory. The mathematical calculations are so precise that
they are used in calculating big problems (concerning gravity) like rocket
launches, calculating the age of meteors, age of orbits and so much more.
So, why do we need general relativity at all? Well, even
though Newton’s idea was correct and widely accepted, there were still a few
things to consider, like space and time being absolute and how does even the
mystic force (gravity) forms or exists?
And this is where Einstein and his great theory came in. According to Einstein, space and time are connected and are relative to each other. He combined space and time into a singular dimension called the space-time dimension.
Despite Newton, who assumed that space and time are absolute,
there was Einstein who corrected him by combining space and time as a singular
form just like he did to mass and energy. (E=mc2)
To understand the general theory of relativity, we must
consider space and time as singular dimensions and relative to each other. So,
what is space-time we may ask?
Space-time is a fabric just like an ordinary carpet in our
house and the objects in this universe are like small particles (eg: dust,
balls, and others) which are present in the carpet. See, Newton derived the
formula of gravity but never explained how that works, but Einstein’s
relativity is a little dig deep into Newton’s foundation where he explained how
gravity works, explaining how one body attracts others.
HOW DOES GRAVITY WORK?
The question of how gravity works are still uncleared, but
it is way easier to understand the parts of it by Einstein’s form.
To understand what gravity is, we can use a very famous idea
that Einstein himself thought of and many physicists appreciate it too.
Let’s say, there is a trampoline in our backyard and we are
given several balls (all balls have different masses).
We are now supposed to put the heaviest ball on the center of the trampoline.
Now obviously, the heaviest ball (at the center) bends the trampoline.
After you’ve put the heaviest ball on the center, it is time for the light balls to be added to the sides of the trampoline. When you put the light balls on the trampoline, you can see the light balls are attracted to the center (heaviest ball). This is because of the heavier ball, as it bends the trampoline and since the other balls are lighter, they are attracted to the center and notice that the attraction is centrifugal force, so that is why it is circling it.
Now, consider the heavier ball is the Sun and the other
light balls are planets, meteors, comets and the trampoline is Space itself.
This is exactly the previous scenario, the Sun is so big and heavy that it
physically bends the space-time itself and creates a curve, and the other
planets or light particles are attracted because of that curve and the
attraction is the centrifugal force itself.
This is gravity according to Einstein, who believed that
despite the invisible force assumed by Newton which attracts the bodies, it is
space itself, which is creating gravity by bending itself.
It
is kind of unbelievable if we think about space being curved which is nothing
but a vacuum bent by a heavy body, but it is proved both experimentally and
theoretically, also space is not empty which is related to quantum mechanics.
In short, general relativity says that space is a medium,
where gravity is formed whenever a rigid mass or energy bends the edge of space
itself and creates a centrifugal force. Even though it is a derivative of
Newton’s gravitation, a lot of theories and experiments were originated from
this theory. In fact, according to Einstein, gravity bends the light itself due
to the curvature of space-time. Since, space is a medium and light is a
material that travels in that medium, bending space(medium) means bending of
light (materials on that space).
HOW DOES GRAVITY BEND LIGHT?
If you are into classical physics or studied the properties
of electromagnetic waves, you know that light is very weird, sometimes it acts
as a wave whereas sometimes it acts as a particle. But, the bending of light is
a top-level weirdness for everyone. How does a path of a massless wave/particle
be disturbed by the force of gravity?
To understand this phenomenon, we need to consider an
example:
Let’s assume, you have a table lying straight in front of
you and the table has some spilled water.
Now, if you were to bend the table slightly inverted then
you can observe that the water which was spilled also bends towards the
direction of the table. In common sense, since we change the table, the direction
of the particle (in this case the water) also tends to change the direction concerning
the table.
This is exactly with light since light travels in space, so bending space means bending the constituents of space-time. As the heavier mass like planets bends the space, the light passing through that planet also bends because of the gravity.
Gravity bending the light was a big breakthrough for all physicists which gave birth to lots of theories in modern physics, it was proved experimentally by astrophysicists and gave recognition to Einstein’s general theory. Overall, this experiment supported the idea that mass bends space and creates gravity.
The mass of the black hole is incredibly large, so large that it bents the space-time way deep than any other particles in space. As gravity is an effect of the body’s mass, the blackholes create a very strong gravitational pull that even light cannot escape (light is affected by gravity because the mass/gravity of the black hole bends the space-time fabric).
Many physicists believe that black holes create so huge ripple to space that they connect two universes acting as a broad pathway, but since no one can travel inside the black hole physically, this is just a theory.
PRESSURE EXERTION BY A PARTICLE:
From here, I put my hypothetical
ideas… it is just an idea, so it can be wrong or right.
When space-time is bent by a heavy body, it creates pressure
underneath. So, we can calculate the amount of pressure exerted by a specific
body when it bends the space. We may wonder, why do we need to calculate the
pressure of a body? Well, from my point of view pressure is related to gravity
and mass, and by calculating the pressure exertion we can also find other
things like time dilation.
PRESSURE CHANGING:
We know,
Pressure = Force
÷ Area ---------------eqn1.
Area of a Sphere=4πr2----------------------------eqn2.
Pressure =1/r2
From this equation, we can say that pressure is
indirectly/inversely proportional to the area of a body. If the body is a
sphere (planet shape) then the area is 4πr2
and from that, we can say that the pressure is inverse to the radius.
Now, let’s say the mass of a ball is constant (force= constant)
but its radius is slowly decreasing. Since the radius is decreasing, the area
decreases, hence the pressure increases.
Hence, if the area/radius of the body decreases the pressure
exerted by that body increases. The strange thing is that somehow changing
pressure increase gravity. See, there’s a theory(proved) called ‘Schwarzschild radius’ which says
that everybody has its limit radius called Schwarzschild radius, and when the
radius of a particular body decreases and becomes closer to Schwartz, the
object becomes a black hole. This is a legit theory that is proved
theoretically and explains some of the basic nature of pressure. But, it
doesn’t give a logical explanation of how exactly changing radius increases
gravity.
When the radius changes (closer to Schwarzschild), the pressure of
the body increases so rapidly that it is equal to the pressure exerted by a
black hole (pressure exerted by the black hole is the pressure of a black hole
bending the space.)
The huge pressure of the black hole is equal to the pressure
exerted by that highly dense Schwarzschild body.
PRESSURE
RELATION WITH GRAVITY?
Pressure is directly related to gravity and can increase and decrease the strength by changing its radius or area.
According to the above figure, we now know that radius can change
gravity. But how we may ask?
As I said earlier, we are considering gravity as the bent of
space-time. As the radius decreases, the pressure of the body increases (from
eqn3), and if the pressure increases then it bends the space-time more.
Radius ∝ 1/(Pressure)
Radius ∝ 1/(Gravity)
So,
Pressure ∝ Gravity
Just like in the figure, the pressure of B is way more than the
pressure of A which is why body B has more gravity. By
this, we can say that when the radius of the body decreases, the pressure
increases, and with that pressure increase it bents the space-time fabric more
and since the gravity is a bending of space, we can say pressure changes
gravity.
In short, if we somehow changed the radius of a body then it increases
the body’s pressure and with that increase in pressure, the space-time bends
more and when the space-time is more bent, gravity is increased.
There
are still major points that I want to talk about pressure like how it changes with
speed and time dilation, but I will cover it in the next blog.
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