Relativity & Cosmology

Light travels with a finite speed. What it means is that whatever we see is information from the past. When we see the Sun or a tree close to us, we are seeing an image of it from the past.
But the speed of light is enormously high. So people were not able to measure it until 1668 to 1676 in spite of many prominent physicists such as Isaac Beeckman in 1629 and astronomers such as Galileo in 1638, attempted to find it out.
It is Danish astronomer Ole Rømer who made the first successful measurement of it and published it. He did it when tracing the orbits of Io and other Galilean satellites of Jupiter. But he did not get the precise numerical value of the speed of light as he did not know the distance of the satellite from the Earth. But his peers , mainly Christiaan Huygens and Edmund Halley were able to find out the exact numerical value of it. Read more...➔

Albert Einstein published the theory of Special Relativity in 1905 in two papers successively and is one of the most influencial theories ever produced in the discipline of physics.
Special Relativity was propounded to deal with how speed affects the time, space , mass and energy. Classical mechanics (laws of motion proposed by Newton) explains very well about the scenarios or events where the speeds that we experience in everyday life are involved. Even we are launching the satellites into the space from Earth using the Newton's mechanics.
But if you have to deal with situations involving speeds closer to the speed of light, you need a new way to describe them. That is where the Special Relativity comes into picture. Read more...➔

Light experiences Doppler Effect when traveling through the space and this results in the red and blue shift of the light frequency. But what is Doppler Effect first of all ?
When the source of the sound moves towards you or else if you move towards the source of the sound , you will hear the sound at a higher frequency (or pitch) , similarly when the source of the sound is moving away from you or else if you are moving away from the source of the sound , you will hear the sound at a lower frequency ( or pitch). This is called Doppler effect.
Let us say the source of the sound is at a standstill and the sound emitted by the source is moving at a speed v , with the fequency of the sound being f_s and the wavelength of the sound being λ_s. You are moving towards the source at a speed v_a. The original frequency of the sound that you hear when you are not moving is f_s. Read more...➔

Blackbody radiation is nothing but the phenomena where the surface absorbs all the electromagnetic radiation (all the light) falling upon it. The fact that light can behave like particles is proved experimentally by examining the radiation spectrum of light emitted by every object. In addition to proving the particle nature of light, the investigation on the blackbody radiation gave rise to the field of Quantum Physics.
Every object above the absolute temperature of zero (0°K) emits radiation in the infrared range. The spectrum of that radiated light was studied by Physicists and they found it to be varying based on the temperature of the object. A perfect blackbody is any object that emits all the light that is incident on it from the environment around it. Read more...➔

Cosmic microwave background radiation (CMBR) is a revealing informative residual from the very earliest time of the universe , almost from the birthing time of the universe. It was first detected in 1964. Its timeless existence is an irrefutable evidence that the universe originated from an extremely hot compressed point-sized origin or beginning. At the outset, Universe must have consisted of extremely hot radiation of plasma, elementary particles, photons (electromagnetic radiation) so as to have produced the CMBR which has almost uniform temperature and wavelengths in the radio region of the electromagnetic spectrum. So There were no galaxies, stars, planets or any other objects in the Universe in the beginning. Read more...➔