Photon have mass?

Photon have mass?

    physics knowledge zone
  • Photon is an elementary and stable particle.
  • It have no mass at rest.
  • It have no charge.
  • In empty space, it travel at the speed of light(c)
It's energy and momentum is related by below equation:


Where-  E= energy of photon
              P= magnitude of the momentum
              C= speed of the light

The equation foe relativistic relation is given blow:

physics knowledge zone

A photon have dual nature: Wave and Particle. A photon is described by wave vector in quantum field theory.
The energy and momentum of a photon depends only on its frequency or inversely, its wavelength

          E=hv =hc/λ

So, Photon have no mass but it have momentum.

Photon have also a different quantity called spin angular momentum which not depends on frequency. The magnitude of the spin is root2h and the component measured along the direction of motion, it's helicity, must be +or-h. There are two possible helicity which called right handed and left handed.

Many people say that photon have mass. If a photon did have mass then it would not move at the speed of light in vacume. It would slower than c and depends on its frequency and also coulomb's law would be modified and the electromagnetic field would have an extra physical digree of freedom.

The Maxwell theory predicts that the energy of light wave depends on its intensity, not on its frequency. But after some time, many experiment show that energy of light wave depends only on its frequency, not on its intensity. After that time, investigation of blackbody, according to Einstein thge energy of any system that absorbs or emits electromagnetic radiation is an integer multiple of an energy quantum:


After that Einstein received the Nobel prize in physics in 1921.

How Many Dimensions Do We Live In ?

How Many Dimensions Do We Live In ?

One of the most confusing, complex and debated question is how many dimensions do we live in ? At first, our common sense tells us that we live in 3 dimensional world as we perceive 3 dimensional things easily but is it some illusions ? Is there some extra dimension that is unknowingly being used to perceive 3 dimensional world ? how many dimensions are there exactly ?
Think about this for a moment, imagine you yourself as a single point and there’s nothing else other than that. As you being a single point, you won’t be able to see yourself ever and no one else could as there’s absolutely nothing else. Imagine there is a line and you are a point on that line. Whether you look to left or right, you would only see single point but never actually a whole line. That’s you being in single dimensional world.

Now, consider there’s a 2 dimensional plane and you as a point part of it. You won’t be able see yourself but from other points you could be seen. On higher level it won’t be possible for anyone being part of that 2 dimensional plane and seeing it completely. To see 2 dimensional plane viewer has to view it from outside of plane. Since, the plane is 2D, to see it completely you need to have a vision from 3rd dimension. For example, say there’s a piece of paper which has rectangle drawn on it. Stick that paper on the wall and try to see drawn rectangle from top view or side view. You always will see a line and not the whole rectangle. But if you see rectangle from front view you will see whole rectangle.
In short, in order to perceive 1 dimensional world, we need access to 2nd dimension and to see 2 dimensional world, we need access to 3rd dimension. So if you want to see nth dimension, you would need vision of n+1th dimension. As we know we can perceive 3 dimensional things, there has to be 4th dimension and this 4th dimension is time !
If you ask us how many dimensions do we live in ? our answer would be we live in 4 dimensional universe with 3 spatial and 1 temporal dimension. But how come time being a 4th dimension ? Imagine you are looking at car that is not moving. You can not be sure weather it is a 2D picture of car or a actual car unless it moves with reference to some point. Its a movement that allows us to infer that our world really does have 3-dimensions, we can move around and we see things moving in a way that clearly must be representative of a 3D world.
Now think about this: What is it that allows movement to be perceived in the first place? Of course, it is time, because movement doesn’t make sense to us without time. So, in a sense, we do experience a 3D world using our vision, but not directly a world with 3 spatial dimensions, instead we perceive directly a world with 2 spatial and 1 temporal dimension which allows us to infer the existence of the third spatial dimension.

The Great Attractor: Gravity Anomaly Pulling Us Us Towards It At 600Kms/s

The Great Attractor: Gravity Anomaly Pulling Us Us Towards It At 600Kms/s

There’s something out there known as The Great Attractor SO massive that it’s pulling on every object within hundreds of millions of light years. But we can’t see it! But Why ? No, it’s not a black hole if you are thinking about it.
There’s a direct relation between mass of an object and gravitation pull produced because of that mass. So, more the massive object (not huge always) , more the gravitational pull. Simplest example is black hole who has huge mass concentrated in tiny little size but has gravitation pull so strong that even light can’t escape from it.
The Great Attractor – an object with such a ultra huge mass that it’s pulling on everybody withing range of hundreds of millions of light years. We cannot see it as our own galaxy’s plane is blocking the radiations coming from that massive body. Scary thing about this is that it’s only 200 million light years away !

Initially, scientists thought that this pull is because of Virgo Supercluster which we are part of but problem was, this super cluster’s mass is not sufficient enough to drag us there at such enormous speed. That implied there had to be something even BIGGER than the super cluster.
Currently, there’s one super cluster known as Shapley Supercluster which is millions of times massive than our milky way galaxy and compared to virgo super cluster, it’s like small peanut to burj al (dubai’s tallest skyscraper). Scientists believe that it’s the most massive thing in the entire observable universe.
So question is, who is giving us the Peculiar velocity (who is pulling us) . This Shapley supercluster ? is it great attractor or there’s something else which is currently hidden to us ? Fact is we don’t know yet !

Time Runs Slower In Space – The Time Dilation Effect

Time Runs Slower In Space – The Time Dilation Effect

Having fun with your friends but time seems to fly so fast. You are close to complete a level in a game but suddenly the timer starts moving super-fast. But in some cases you think time is not passing by. Best example would be when you sit for a lecture in school or college but time does not pass by.
We all know the rate at which time passes is constant for all of us. So whether it is a lecture or a game you are playing the time moves at the same rate. But certainly we don’t feel it that way.
Suppose you are shown five boxes from a distance one after the other and from the five boxes one box is shown to be moving towards you. One would certainly feel the box that was coming to you appeared to be there for more time than the other four boxes. But it was not so. The time for which each individual box that was shown to you was the same that the box which was coming towards you appeared to be. This is nothing but the time dilation effect in psychology.
Time Runs Slower In Space ?
Einstein’s theory of relativity also shows that faster something travels the slower time appears to move. Suppose you are on earth holding a clock and a friend of yours is in a space rocket which is passing by at nearly 150000 miles per second and she also has a watch with her. If supposing you are able to see your friends watch you would notice that the time moving in her watch is very slow as compared to yours.
To test this time dilation effect various experiments were conducted where atomic clocks were used on airplanes going around the world. The timings of these clocks were compared to the time of clocks kept at a national observatory in Washington, DC. And what Einstein has thought it was actually found the clocks in the airplane seemed to move slower.
Scientists have found various mathematical or space travel techniques to prove this time dilation effect. It is found that if a person travels for a year at 95% the speed of light, he would age one year, but people on earth would age 3.2 years. And even if the person travels at 50% the speed of light, people on earth would age 1.15 years. This effect cannot only be studied through space travel. But now scientist have also found a way to prove the same thing on earth in a lab.

What If You Were Born In Space ?

What If You Were Born In Space ?

Imagine someone asked you which is your birthplace? And you are like I’m born in space. Doesn’t this sound interesting?
First let us look at how many people are already there in space. The first person who went to outer space 52 years ago, after that more than 500 people have left the earth and have gone as far as the moon. So from the past few years there has been a continuous uninterrupted presence of humans living in space. But all these people who have gone out or are present on earth are born on this planet earth.
But what if someone is born in space? How suited is our biology for the outer space we were born into? But where do we consider this outer space to be? Outer space is about one hundred thousand meters above your head.
We all believe that the people who are in space are floating around because there is no gravity. But this is a very big misconception as there is plenty of gravity as it is on earth. They are not floating, rather they are just falling due to the orbital speed. An orbital speed is a speed which is so fast that even while falling you don’t, because the earth literally curves away from you as fast as you fall towards it. So we cannot say that there is no gravity in space but we can say that it is a zero g environment where g is acceleration.
So if the gravity is pretty much the same as earth how would a human look like if they were born in space? To understand how humans would look, it would require us to understand first what effect weightlessness has on the human body. Even mere hugging each other in space is difficult but a recent invention called the ‘2-suit’ might make it easier. This invention provides effortless intimacy in a weightless environment.
A baby inside mothers needs the development of the vestibular system. Canals in the inner ear that uses the flow of fluid to determine movement and balance. In a zero g environment i.e. Space the fluid required would just float around and this can lead to motion sickness, visual illusions and disorientation. This was experimented with the help of pregnant rats. Pregnant rats taken to space when gave birth to babies struggled with directions. Vestibular fluid is not the only fluid that would affect the babies born in space, but there are other fluids as well, which would get affected by a zero-g environment. So this zero-g environment gives the babies a puffy face due to the floating fluids and all of those fluid pressure on your face can also affect the vision.
These are not the only side effects of space. Even astronauts who had long flights and returned back to earth were tested. Almost everyone had visual problems. An astronaut can even lose about 22% of their total blood volume while in space. Also the radiation from the sun and the rest of the universe can be dangerous for the human body and we are still not sure how to safeguard ourselves from these radiations.

As for the shape of the human body, full grown astronauts in orbit, no longer pressed down by earth typical gravitational force experience spinal expansion as much as 3 percent before they come back to earth. Even a person as tall as 6 feet can go to space and return as tall as 6 feet 2 inches. In a weightless environment you don’t need much muscle strength to move around, so your muscle strength in space to weaken. All of these reasons sound scary to live in space.
We all understood that these problems affect the adults in space and pretty much the same way it would affect a developing baby in space. So a baby born in space would might look like this because of the active forces required for developing healthy bone structure would just not be there.
Many studies have been done on this topic and some are even planned for the future as we don’t even know that a healthy fetus can develop in space or even conception can even occur in space. So let’s wait and see if all this can happen in future.

Albert Einstein and the Theory of Relativity

Albert Einstein and the Theory of Relaivity

Elbert Einstein gives his Special Theory of Relativity in 1905 and his General Theory of Relativity in 1915. The first showed that Newton's three laws of motion were only Approximately correct,breaking down when velocities approached that of light. The second showed that Newton's Law of Gravitation was also only approximately correct, breaking down in the presence of very strong gravitational fields

                                                                                        Newton vs. Einstein: Albert's Turn to Kick Butt

 Here, I only summarize the differences between Newton's theory of gravitation and the theory of gravitation implied by the General Theory of Relativity. They make essentially identical predictions as long as the strength of the gravitational field is weak, which is our usual experience. However, there are three crucial predictions, where the two theories diverge, and thus can be tested with careful experiments.

Albert Einstein and the Theory of Relaivity
Precession of Perihelion
  1. The orientation of Mercury's orbit is found to precess in space over time, as indicated in the adjacent figure (the magnitude of the effect is greatly exaggerated in this figure). This is commonly called the "precession of the perihelion", because it causes the position of the perihelion to move. Only part of this can be accounted for by perturbations in Newton's theory. There is an extra 43 seconds of arc per century in this precession that is predicted by the Theory of General Relativity and observed to occur (a second of arc is 1/3600 of an angular degree). This effect is extremely small, but the measurements are very precise and can detect such small effects very well.

Albert Einstein and the Theory of Relaivity
2. Einstein's theory predicts that the direction of light propagation should be changed in a gravitational field, contrary to the Newtonian predictions. Precise observations indicate that Einstein is right, both about the effect and its magnitude. A striking consequence is gravitational lensing.

Albert Einstein and the Theory of Relaivity
    3. His General Theory of Relativity predicts that light coming from a strong gravitational field should have its wavelength shifted to larger values (what astronomers call a "red shift"), again contrary to Newton's theory. Once again, detailed observations indicate such a red shift, and that its magnitude is correctly given by Einstein's theory.

    Albert Einstein and the Theory of Relaivity
    4. The electromagnetic field can have wave in it that carry energy and that we call light. Likewise, the gravitational field can have waves that carry energy and are called gravitational waves. These may be thought of as ripples in the curvature of space-time that travel at the speed of light.

    Just as accelerating charges can emit electromagnetic waves, accelerating masses can emit gravitational waves. However, gravitational waves are difficult to detect because they are very weak and no conclusive evidence has yet been reported for their direct observation. They have been observed indirectly in the binary pulsar. Because the arrival time of pulses from the pulsar can be measured very precisely, it can be determined that the period of the binary system is gradually decreasing. It is found that the rate of period change (about 75 millionths of a second each year) is what would be expected for energy being lost to gravitational radiation, as predicted by the Theory of General Relativity.