Below are five tables that summarize five basic formulas of Special Relativity. If you want to try them out, fill in the data fields and click the "calculate" button.

Those five formulas are intimately bound. If you would take only one of them into consideration then you could easily demonstrate special relativity is a nonsense. But if you are using them altogether then everything becomes fluent and perfectly logical.

The speed of light is represented by the symbol c. That's 299,792,458 m/s (in vacuum).

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	Length contraction:  Let's consider a rocket. For any person motionless compared to the rocket, it has a length of l0. When it will be traveling at speed v compared to you, you will see it now has a shorter length of l. (The diameter of the rocket did not change.) In other words : when the rocket was at rest next you, it had a length of l0. Now it shears at a high speed v past you, you will see or measure it has a length of l. Yet a person onboard the rocket will still claim it has a length of l0
Length of rocket when motionless compared to you:   m  Speed it now travels at:   m/s   length of traveling rocket for you:   m
This fact has no feelable impact on everyday life. But let's imagine a 10 km long train. When it stands still its rear is located at Chasmton and its front is located at Summerville. Now suppose the train speeds at 100,000,000 m/s. Well at the moment the mayor of Chasmton sees the back of the train at Chasmton, the mayor of Summerville will see the front of the train about 500 meters before Summerville. The train is shorter. Reciprocally, people on board the train state that when the back was at Chasmton, the front was already about 500 meters past Summerville. They see the distance between Chasmton and Summerville to be shorter.

	Time dilation:  If an hourglass lasts t0 second when it is in your hand, then onboard a rocket at speed v you will see it last longer: t seconds. (Yet for any person onboard the rocket it still lasts t0 second.)
Time an hourglass lasts when in your hand:   s  Speed of the rocket it now travels inside:   m/s   time you see the hourglass now last:   s
One consequence of that phenomenon is that the clocks on board of a satellite run slower. You must take that into account when you make calculations based on the satellite's clock. For example if the satellites tells you "With my telescope I saw your breakfast took 527.2358801 seconds". That means if you had measured that time yourself you would have come out with a number of 527.2358800 seconds (low orbit satellites travel at 7.000 m/s). Reciprocally, imagine you look with a telescope towards a lamp that lights and dims aboard the satellite. Say you measure the time the light is on and come out with a result of 100.000000027 seconds. You phone the satellite and tell him that. He will respond to you: "Ehr, well no, I measured 100.000000000 seconds. My clock is very accurate you know.". If both of you know of Special Relativity, you'll know all this is normal.

	Time shift:  You put two clocks a distance d apart along a rocket's body. If the rocket now travels at a speed v compared to you and everybody onboard the rocket says the clocks are synchronized, then you will see the clocks are not synchronized: the clock forwards is back of t seconds.
Distance between two clocks along rocket body:   m  Speed the rocket now travels at:   m/s   shift you see clock at front now has:   s
That phenomenon is used inside high precision inertial platforms for airplanes. Several clocks are placed apart from each other and a central circuit compares their signals. If one clock seems to hold up then the circuit can calculate the airplane accelerated in that direction. This is very important to understand Relativity is a logical and fluid system. Before he understood this clock phenomenon Albert Einstein even thought of suicide. Take for example the speeding train between Chasmton and Summerville. How is it on Earth possible that at the very moment the back of the train is at Summerville, people aboard the train tell the front of the train is 500 meters past Chasmton and people of Chasmton tell the train is 500 meters before Chasmton? Nonsense! Well it becomes logical if you take into account the clock in front of the train runs back a little. So, if a voyager at the back of the train says "At 4 pm exactly the back was exactly at Summerville.", the driver in front of the train will respond: "Well at 4 pm exactly we were 500 past Chasmton.". That's quite normal, since the driver's clock runs back a little. Anyway, that's what people of Chasmton and Summerville see when they look through the train's windows and look at the clocks inside the train. But the people aboard the train see their clocks are synchronized, whatever experiment they perform. For example they can light a flash bulb just in the middle of the train, the driver at the front and the voyager at the back press their clocks' button to synchronize just when they see the flash. Or they can both walk towards the middle of the train, meet and synchronize their clocks, then go back to their positions. Or they can use the train's phone system, send each other a top signal and take into account those signals take some time to travel back and forth. People aboard the train tell for sure their clocks are synchronized. Reciprocally, when they look at the people of Chasmtom and Summerville's clocks, they see the clocks of Chasmton run back a little. So they can tell them: "Well, we understand you believe the train's front was 500 meters before Chasmtom. That's because the clocks of Chasmtom run back a little compared to those of Summerville. But when people of Chasmton and Summerville check that out, they will come out with the result their clocks are perfectly synchronized. Nobody has the privilege of absolute synchronicity. That's the world of Special Relativity. If the train stops, then its clocks will no more appear to be synchronized. If the driver and the voyager walk towards the center of the train and compare their clocks, they realize the driver's clock runs back a little. Suppose they synchronize their clocks, go back to their positions and start the train again up to a speed of 100,000,000 m/s. People of Chasmton and Summerville see the clocks aboard the train are synchronized. But if the driver and the voyager meet once again in the middle of the train, they will see now the driver's clock runs forwards a little. The people of Chasmtom and Summerville know why. They saw it happen. Clocks traveling at high speed run slower. When the voyager walked towards the middle of the train his walk speed was added to that of the train. So his clock ran even slower. While the driver's clock ran a little faster since his walk speed was subtracted from the train's speed. When they meet in the middle, the driver will tune his clock back a little, to synchronize with the voyager's clock. Now they see their clocks are synchronized. Even if they go back to their positions and check it by any means. But people of Chasmton and Summerville see the driver's clock runs back a little compare to the clock of the voyager. And so on...

	Speed contraction:  If a rocket travels at a speed v compared to you and a snooker ball is made to roll on the rocket's flour towards the front and the passengers of the rocket say the ball rolls with a speed vm compared to them, then vs is the speed of the ball compared to you.
Speed of the ball measured aboard the rocket:   m/s  Speed the rocket travels at:   m/s   speed of the ball for you:   m/s
This formula is one way to check the fact it is not possible to attain the speed of light. Suppose a canon is build to fire shells at 200,000,000 m/s. A rocket travels at a speed of 200,000,000 m/s compared to you and carries the canon. When it fires a shell forwards, you will see the shell travel at 276,805,111 m/s, which is less than c.

	Mass increase:  If an object has a mass m0 when it is motionless compared to you, then it will have an increased mass m when it moves at a speed v compared to you.
Weight of rocket when motionless for you:   kg  Speed the rocket now travels at:   m/s   weight the rocket now has for you:   kg
That phenomenon explains why you are several tens of kilograms heavy. Indeed, would the quarks you are made of be motionless then you would weight less than a kilogram. But they turn around each other at a speed very close to the speed of light. That makes them become very heavy. Most of your weight is due to that relativistic phenomenon.

Galilean Relativity states the following:

• Whatever steady speed a closed laboratory moves, any experiment you do inside the laboratory will give the same result. So you will never be able to determine at what steady speed that laboratory moves just by doing experiments inside the laboratory.

• Whatever place you put a closed laboratory, any experiment you do inside the laboratory will give the same result. So you will never be able to determine where the laboratory is just by doing experiments inside the laboratory.

• Whatever direction you turn a closed laboratory, any experiment you do inside the laboratory will give the same result. So you will never be able to determine what direction the laboratory door is directed just by doing experiments inside the laboratory.

Special Relativity adds the following:

• Any laboratory, moving at any constant speed towards any constant direction, measuring the speed of some light produced by any other laboratory will always measure that speed to be 299,792,458 m/s.

In order to keep this rule true, the Universe squeezes every objects. And changes the speed of every clock.

General Relativity adds the following:

• A little and closed laboratory cannot know whether it is placed aboard an accelerating rocket, sitting on the surface of a planet or placed on the edge of a huge rotating wheel.

This implies once more objects squeezing and clock speed changes. For example clocks on Earth run a little slower than clocks on the Moon. Even space itself is bend and curved.

General Relativity is shipped with an impressive calculation system. It can compute out just any situation: accelerating or turning laboratories, electromagnetic or gravitational fields, encounters with big masses... Yet it can be quite difficult to handle.

That statement of objects, clocks and space being squeezed by the Universe is just a way to express the reality. There are other ways round to describe the reality; other points of view, that come out with the same physical results. Be open to them.

Maybe you conclude the Universe simply cannot behave like a Tex Avery cartoon and the content of texts like this one must be erroneous. First of all, in a Tex Avery cartoon the characters squeeze and expand at random. While in the Universe it happens a very accurate, mathematic and reproducible way. Second, this all has been tested out thoroughly. From the faintest atomic phenomenon up to stars and galaxies, till now everything seems to obey the formulas of Relativity. Never ever has a single phenomenon been found that would not glue to the formulas of Relativity. Except maybe this one: an ESA funded research measured the gravitational equivalent of a magnetic field. The effect is much larger than expected from General Relativity. Article.