The Bending of Light in a Gravitational Field

Let us consider a ray of light that shines through a window in an elevator at rest, as shown in figure. The ray of light follows a straight line path and hits the opposite wall of the elevator at the point P.

Let us now repeat the experiment, but let the elevator accelerate upward very rapidly, as shown in figure. The ray of light enters the window as before, but before it can cross the room to the opposite wall the elevator is displaced upward because of the acceleration. Instead of the ray of light hitting the wall at the point P, it hits at some lower point Q because of the upward acceleration of the elevator.

To an observer in the elevator, the ray of light follows the parabolic path, as shown in figure. Thus, in the accelerated coordinate system of the elevator, light does not travel in a straight line, but instead follows a curved path. But by the principle of equivalence the accelerated elevator can be replaced by a gravitational field. Therefore light should be bent from a straight line path in the presence of a gravitational field.

The gravitational field of the earth is relatively small and the bending cannot be measured on earth. However, the gravitational field of the sun is much larger and Einstein predicted in 1916 that rays of light that pass close to the sun should be bent by the gravitational field of the sun.

Another way of considering this bending of light is to say that light has energy and energy can be equated to mass, thus the light-mass should be attracted to the sun. Finally, we can think of this bending of light in terms of the curvature of spacetime caused by the mass of the sun. Light follows the shortest path, called a geodesic, and is thus bent by the curvature of spacetime.

Regardless of which conceptual picture we pick, Einstein predicted that a ray of light should be deflected by the sun by the angle of 1.75 seconds of arc. In order to observe this deflection it was necessary to measure the angular deviation between two stars when they are far removed from the sun, and then measure the deflection again when they are close to the sun. Of course when they are close to the sun, there is too much light from the sun to be able to see the stars.

Hence, to test out Einstein’s prediction it was necessary to measure the separation during a total eclipse of the sun. Sir Arthur Eddington led an expedition to the west coast of Africa for the solar eclipse of May 29, 1919, and measured the deflection. On November 6, 1919, the confirmation of Einstein’s prediction of the bending of light was announced to the world.

More modern techniques used today measure radio waves from the two quasars, 3c273 and 3c279 in the constellation of Virgo.

A quasar is a quasi-stellar object, a star that emits very large quantities of radio waves. Because the sun is very dim in the emission of radio waves, radio astronomers do not have to wait for an eclipse to measure the angular separation but can measure it at any time.

On October 8, 1972, when the quasars were close to the sun, radio astronomers measured the angular separation between 3c273 and 3c279 in radio waves and found that the change in the angular separation caused by the bending of the radio waves around the sun was 1.73 seconds of arc, in agreement with the general theory of relativity.


TIME TRAVEL & WORMHOLES – myth or truth

At present, we are changing according to the time. Time not change according to us. But what if we change the time. Time travel An imaginary thought.

We don’t know if It will be future or past. It is like changing time’s direction to past or increasing time’s speed to future, but if it will be possible in the future, It may be travel to past.

According to relativity, Nothing can travel faster than light (3 × 10⁸m/sec.). At light speed, mass will be infinite (according to relativistic mass formula) . And the length of object will be zero (according to length contraction formula). But if we travel with the light speed, what can we see? Is there any color? Is there any boundary of anything? Only white light appears on moving with light speed. Everything is white.

At present, black holes are the best source to see the past. Where, light cannot even pass through. The body’s shape , space-time will be changed at light speed . 

Even if we travel with such a high-speed it will take 2000 years in reaching and coming back to Earth from a thousand light years away star(or any Terrestrial body in space). When you travel such a large distance, an atom, the smallest unit of matter also traveled to that distance, and it is amazing to imagine.


According to scientists, a wormhole is a cylindrical path between two heavy bodies in space. It is not from any science fiction movie. It is scientist’s thoughts. 

Wormhole forms by two giant bodies have very high gravity value like black holes. If a path is a thousand light years long, wormholes can make it a few million miles long. So, it may be a possibility to travel faster than light.

In 1835, Albert Einstein and Nathan Rosen called them Einstein-Rosen Bridge. Bridge that connects two, bodies that are light years far away from each others.

Worm holes are like tunnels in space connecting to distant bodies because space and time are flexible (according to Einstein). Through the wormholes we can cover very long distance in a very short period.


According to another theory we can travel with light speed. The theory proposed that, if we are stable and space can move. In this theory, a large heavy body contract the space with fast and alternately a negative mass, behind the large body, can expand that contracted space.

Negative mass is only a hypothetical Idea. It behaves just opposite of positive mass that we have.

Positive mass can contract the space while a negative mass can expand it. Due to this, we remain stable on a position and space can move.

If all this phenomena possible, we can cover large distance with speed of light by stay at a place without any change.

To be continue…

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When things push against one another, they produce pressure.

Pressure may be a live of what proportion force pushes against every purpose on associate object’s surface. Here on Earth, we have a tendency to square measure beneath constant pressure. Air might sound like emptiness, however it still has mass, therefore gravity pulls it down toward the bottom. This makes gas pressure, a force unfold everywhere your body.

Pressure is what happens once a force pushes on a surface. Additional force makes additional pressure. Once identical force presses over a smaller space, the pressure becomes larger. However if the force is meet a bigger space, the pressure reduces. Sometimes, we do not notice pressure till the force is discharged.

Person will simply stand on a bed of nails. Their body has weight, which implies gravity pulls it down with tons of force. however after they stand on many nails, their weight is shared across all. The pressure on every nail is incredibly little, so that they aren’t getting scraped.

Life would be not possible while not pressure. Blood flows around your body as a result of your heart pumps it with enough pressure to succeed in your fingers and toes. Water will flow to your home as a result of it’s hold on high in reservoirs and tanks. Gravity pulls the water down, giving it pressure that produces it spray from the tap. Pressure is additionally wont to create several tools work, from vacuum cleaners to pushpins, and automotive engines to airplanes.

Air on top of pressure is formed by the burden of air you. If you climb a mountain, there’s less air on top of you, and so less gas pressure. It’s more durable for air to induce into your body and more durable for you to breathe. High within the sky, there’s hardly any gas pressure, and respiratory is nearly not possible. Planes have their compartments controlled by pumps therefore individuals within will breathe commonly.

Air pressure changes our weather. Air mass brings storms and rain. a
Air mass suggests that sunshine. We are able to predict the weather employing a measuring device to live gas pressure. Within this one may be a box stuffed with air. Because the gas pressure changes, the box squeezes in and out. This moves the needle round the dial.

The deeper you dive to a lower place the ocean, the additional pressure there’s. That is as a result of there’s additional water over your head pushing down. Water is denser than air identical quantity of it weighs more-so water pressure affects things over gas pressure. That is why ventilator diverse will go down solely a brief distance, and why submarines want hulls manufactured from sturdy metal to face up to the pressure. during a milk carton, the liquid close to very cheap is squeezed by the burden of the liquid on high.

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Radiation is energy within the kind of waves or streams of particles. There area unit several varieties of radiation all around us. Once individuals hear the word radiation, they usually think about nuclear energy, atomic power and radiation, however radiation has several different forms. Sound and visual light weight area unit acquainted types of radiation: different varieties embody ultraviolet light that produces a suntan), actinic ray (a kind of heat energy), and radio and tv signals.

An atom could be a variant of a selected matter. whereas all isotopes of a given component have constant variety of protons, every atom includes a totally different variety of neutrons.

For example, H has 3 isotopes (or variants):

*Hydrogen-1 (contains one nucleon and no neutrons)

*Hydrogen-2, that is termed Hydrogen atom (contains one nucleon and one neutron).

*Hydrogen-3, that is termed Hydrogen (contains one nucleon and 2 neutrons)

Isotopes that don’t seem to be stable and emit radiation area unit referred to as radioisotopes. A isotope is associate in nursing atom of part that undergoes spontaneous decay and emits radiation because it decays. Throughout the decay method, it becomes less radioactive over time, eventually changing into stable.

There area unit 3 main sorts of radioactive decay:
*Alpha decay:
Radioactive decay happens once the atom ejects a particle from the nucleus, that consists of 2 neutrons and 2 protons. Once this happens, the number decreases by a pair of and also the mass decreases by four. Samples of alpha emitters embody atomic number 88, radon, metallic element and atomic number 90.

*Beta decay:
In basic radioactive decay, a nucleon is become a nucleon associate in nursing an negatron is emitted from the nucleus. The number will increase by one, however the mass solely decreases slightly. samples of pure beta emitters embody strontium-90, carbon-14, hydrogen and sulphur-35.

*Gamma decay:
Gamma decay takes place once there’s residual energy within the nucleus following alpha or radioactive decay, or once nucleon capture (a sort of nuclear reaction) in a very reactor. The residual energy is discharged as a gauge boson of nonparticulate radiation. Gamma decay typically doesn’t have an effect on the mass or number of a isotope. samples of gamma emitters embody iodin. cesium-137, cobalt-60, radium-226 and technetium-99m.

Cancer risk assessment:
The ICRP has calculated the likelihood of fatal cancer by relying totally on the assessment of radiation effects by scientific bodies like UNSCEAR and BEIR. It then determined what it calls the “detriment” of radiation exposure. This includes:

*the likelihood of fatal cancer

*the likelihood of non-fatal cancer

*the likelihood of severe hereditary effects

* the length of life lost if the hurt happens


A blue whale have weigh the maximum amount as twenty elephants, however it’s no drawback floating within the ocean. The large ships that ferry product round the world will hold thousands of big containers while not sinking. Things float if they’re less dense than the fabric around them-that is, if an exact volume of the thing weighs but a similar volume of its surroundings.

Gravity pulls things down, even in water. However water pushes upward against things floating in it. If there’s enough water pressure at a lower place one thing to balance its weight, it floats. Wood is a smaller amount dense than water. The load of a block of wood is a smaller amount than the pressure of the water beneath, therefore it floats. Stone is a lot of dense than water, therefore its weight pulls it down in spite of the pressure of the water beneath.

Heavy things will fly if they will produce enough upward force to elevate their weight. Before planes were made-up, individuals took to the skies in balloons. These soar into the sky once hot air is pumped up within the large material dome. A balloon choked with hot air weighs but a similar balloon choked with cold air. It’s less dense than the air around it, therefore it soars into the sky. huge balloons will produce enough force to hold individuals with them.

The world’s biggest load ships carry up to 18,000 immense containers, every as huge as a truck. Ships work by spreading their weight over a large space. Most of a ship is simply empty house, therefore it weighs but a similar volume of water. Though it’s implausibly significant, it still floats.



When waves of energy vibrate within your ears, you would possibly desire singing or dance. We tend to decision this music. It’s a special reasonably sound that we tend to fancy paying attention to as a result of it’s the ability to create us feel happy or unhappy. Music is formed by instruments that shake the air therefore the sound rushes toward us. Most instruments create a spread of sound frequencies, in order that they will play a musical tune.

Musical instruments create sound by moving the air back and forth all around them. The quicker they vibrate, the quicker they shake the air and also the higher the musical notes we tend to hear. Most instruments area unit designed in order that they will vibrate at slightly completely different speeds, creating many various notes. A stringed instrument has six strings, however you’ll press them in numerous places to create dozens of various notes.

Bottel organ
You’ll build associate organ by filling bottles with completely different amounts of water. Once you blow into a bottle, the air within vibrates, creating a musical notation. The fuller bottles create higher notes, whereas those with less water turn out lower notes.

We can produce associate infinite range of melodies by combining sounds from different instruments. Though every instrument makes sound waves, all of them work slightly otherwise. larger instruments tend to create lower and louder notes than little ones. Instruments with a lot of keys, strings, or holes will create a wider vary of notes. taking part in several instruments along in associate orchestra makes even a lot of fascinating effects.

It takes energy to provide sound, thus creating loud sounds for an extended time is difficult work. that is one reason why we’ve electrical instruments. They use electricity to assist us create loud sounds for long periods of your time.

Electric instruments additionally create terribly completely different sounds from ancient acoustic (nonelectric) instruments.


Ordinary acoustic guitars have strings that you just pluck. Once the strings move, they vibrate air within the wood case and this makes the sound. Electrical guitars have metal strings with pickups (wire-wrapped magnets) beneath. Once the strings vibrate, they create electrical currents flow through the pickups. If a stringed instrument is connected to associate electronic equipment and speaker system, these currents area unit boosted in volume to create loud music.



Magnetism could be a force which will attract (pull toward) or repel (push away). Materials that are powerfully interested in magnetism, like iron or nickel, referred to as magnetism materials.

Repel or attract
A magnet has 2 ends, or poles-a north pole and a South Pole. once 2 magnets placed close to one another with like (the same) poles facing, the 2 poles can push one another away. If a pole is facing a South Pole, they’re going to pull toward one another.

Magnetic field
The area around a magnet wherever a magnetism will be detected is named its field. The field is strongest close to the poles. Dropping iron filings around a magnet reveals the form of its field.

The stronger the magnet, the larger its field are going to be.

Magnets in action
We use magnets in many various ways in which the motors within several machines driven by tiny magnets, whereas giant magnets will power giant objects like trains.

Magnetic Earth
Earth could be a big magnet. It’s encircled by a field, that is made by electrical currents deep within the planet’s liquid metal core. A compass works by sensing Earth’s magnetism. It contains alittle magnet, and therefore the South Pole of the needle points toward Earth’s direction pole.


When you see a airplane sweeping through the sky, or watch a automobile whizzing past, powerful engines area unit athletics within them. Most vehicles area unit supercharged by engines- machines that burn fuel to released heat. Even small amounts of fuel unharness vast amounts of energy after they burn. Engine turns this energy into kinetic (movement) energy.

What’s within associate degree engine?
Engines absorb fuel, burn it to unharness heat, and use that to form movement. In a very automobile engine, these items happen in durable “cooking pots” known as cylinders, with pistons at the lowest that pump up and down. Because the fuel burns, every piston pumps successively, driving a rod known as the rotating shaft. The spinning rotating shaft carries the engine’s power to the gears and wheels.


Automobile engines repeat four steps (strokes). First, within the intake stroke, mixed air and fuel area unit sucked in. Second, within the compression stroke, the piston squashes the mixture. Third, within the power stroke, a electrical device makes the fuel burn, expand, and drive the piston. Finally, within the exhaust stroke, the piston pushes waste gases from the cylinder.

The engines on cars, planes, trains, and rockets all add alternative ways. This is often primarily as a result of larger vehicles ought to build far more power than smaller ones. They need a lot of powerful engines, so that they will burn fuel a lot of quickly, build a lot of energy every second, and go quicker.

How will associate degree engine drive a machine?
Jet engines fireplace exhaust gases backward, that makes planes shoot forward. In cars and trains, the facility from the engine is employed to show the wheels. In ships (right) and tiny planes, the engines flip propellers, pushing air or water to power on.

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Twisting, bending, squashing, and stretching of these things happen thanks to forces. Once you squeeze one thing soft and stretchable, like a rubber ball, it changes form. If you stop compression, you’re taking the force away, and also the ball changes back once more. We are saying the ball is elastic, as a result of it goes back to its original form.

If you apply force to one thing stretchable, as an example by processing into gum, it changes form. If you blow double as laborious, it stretches double the maximum amount. Blow too laborious and it snaps. This basic rule of stretching is termed Hooke’s law, when the mortal Hooke.

Elastic things return to their original form, but not each object is like this. several things merely bend or snap once you push them with an excessive amount of force. we are saying they’re plastic, although they are product of metal or another material. Plastic suggests that things bend for good out of form once you push or pull them.

Pull back on a toy and also the force you employ stretches the elastic. This stores energy within it, referred to as mechanical energy. Once you forgoing, the elastic returns to its original form. The hold on energy should go somewhere—so it’s given to the stone, flinging it through the air.

Pinch your skin and forgoing, and it springs right back once more. This can be as a result of young skin is incredibly elastic. Older skin isn’t as elastic, that is why older folks have additional wrinkles. Antiwrinkle creams work by covering skin in sticky chemicals that stretch it tight. This makes wrinkles disappear a minimum of for a moment.

Rubber are often stretched to 3 times its length.

Hydrogels, the world’s stretchiest materials, are often force to twenty times their original length.


Mirror and reflection

Mirrors play throw and catch with light. They catch light from in front of them and throw it back the way it came. Mirrors are made from thin metal sheets inside glass, but many other surfaces reflect light as well. A smooth lake mirrors the sky above it, and you can often see your face in shiny shoes or a polished spoon.

Light rays stream in straight lines, so a flat and smooth (plane) mirror reflects things much as they are. The reflected image looks like the original because the incoming rays bounce back in parallel lines. However, a mirror that curves inward (concave) makes things look bigger, while one that curves outward (convex) can make them look smaller.

Mirrors reflect heat as well as light. Hot objects give off infrared radiation, which is like invisible, hot light. When infrared hits a mirror, it reflects straight back again. You can test this effect for yourself by wrapping some silver foil around your arm. It feels warm because your body heat is being reflected back.

Cats are like walking mirrors. They can see at night because they have special reflecting surfaces (miniature mirrors) behind their eyes. These catch incoming light and bounce it back out through their eyes again. The light passes through their eyes twice, and this gives them double the chance to see dim objects. That’s why a cat’s eyes shine at night or in dim light.

Some telescopes need giant mirrors, but if a mirror becomes too big, it bends and buckles.

To get around this, the biggest and best space telescopes use mirrors split into dozens of honeycomb-like segments. Bolted onto a framework, very close to one another, they work together like a single giant mirror.