Gravitational time dilation is a physics concept about changes in the passage of time, caused by general relativity. A clock in outer space moves more quickly than a clock on Earth. Heavy things like planets create a gravitational field that slows down time nearby. This means that a clock on a spaceship far away from any planet would move faster than a clock near Earth.
This is different from time dilation explained by special relativity, which says that fast objects move more slowly through time. Close satellites like the International Space Station move very quickly to orbit the Earth, so they are slowed down. Because the ISS is in low Earth orbit (LEO), time dilation due to gravity is not as strong as time dilation due to its speed, so a clock on it is slowed down more than it is sped up. An object in Geostationary orbit moves less quickly and is farther away from Earth, so gravitational time dilation is stronger, and clocks move more quickly than in LEO. This means that engineers need to pick different clocks for different orbits. GPS satellites work because they know about both kinds of time dilation.
Case #1: In special relativity, clocks that are moving run slower, according to a stationary observer's clock. "This effect does not come from workings of the clocks, but from the nature of spacetime".
Case #2: the observers may be in positions with different gravitational masses. In general relativity, clocks that are near a strong gravitational field run slower than clocks in a weaker gravitational field.
Experiments support both aspects of time dilation.
The formula for determining time dilation in special relativity is:
where
It could also be written as:
where
A simple summary is that more time is measured on the clock at rest than the moving clock, therefore, the moving clock is "running slow".
When both clocks are not moving, relative to each other, the two times measured are the same. This can be proven mathematically by
For example:
In a spaceship moving at 99% of the speed of light, a year passes. How much time will pass on earth?
Substituting into :formula_1
So approximately 7.09 years will pass on earth, for each year in the spaceship.
In ordinary life today, time dilation had not been a factor, where people move at speeds much less than the speed of light, the speeds are not great enough to produce any detectable time dilation effects. Such vanishingly small effects can be safely ignored. It is only when an object approaches speeds on the order of (10% the speed of light) that time dilation becomes important.
However, there are practical uses of time dilation. A big example is with keeping the clocks on GPS satellites accurate. Without accounting for time dilation, the GPS result would be useless, because time runs faster on satellites so far from Earth's gravity. GPS devices would calculate the wrong position due to the time difference if the space clocks were not set to run slower on Earth to offset the quicker time in high Earth orbit (geostationary orbit).
Supreme Court of the United States
The Supreme Court of the United States is the highest court in the United States of America. Because of this, the Court leads the Judicial Branch of the United States Federal Government. It is the only U.S. court established by the United States Constitution. Its decisions are supposed to be followed by all other courts in the United States. The Court meets in its own building in Washington, D.C. However, until 1935, the Supreme Court met in the United States Capitol.
There are 9 justices on the court now: one Chief Justice and eight Associate Justices. The most recent justice, Amy Coney Barrett, replaced Ruth Bader Ginsburg after she died. Courts are unofficially named for the Chief Justice; the current Court is called the "Roberts Court" after Chief Justice John Roberts.
The Supreme Court chooses which cases it will decide on. Many people ask the Supreme Court to decide their cases, but the court refuses most of them. For the Supreme Court to decide a case, the case must be about federal law or be about the laws of more than one state. Cases must first be decided by a federal District Court and a federal Court of Appeals or by a state supreme court. Even after that, the Supreme Court can choose not to decide a case for any reason. There are some cases that can start in the Supreme Court and that the Supreme Court must decide, but those are usually rare.
The justices serve for life unless they want to retire earlier or are impeached. If a justice retires, he or she can still be asked to serve as a judge on a federal Court of Appeals. New justices are nominated (picked) by the President of the United States, and then must be approved by the United States Senate.
The current court is named "The Roberts Court" named after Chief Justice John Roberts.
Fall (motion)
A fall is, in everyday language and thought, a movement down that happens due to gravity. An example is when something rolls off a table and falls down to the floor.
Falling is a motion towards a place where an object will have a lower total potential energy or lower potential. Total potential energy being the sum of all potential energies -- those from gravitational fields, electric fields, and magnetic fields.
The idea of falling in natural human language(s) as falling down begs the definition of what down really is. What is down in natural human language(s)? Down may be straight towards your feet, or if you are on a hill, be off at an angle. Often an attempt is made to correct this definition by saying down is towards the center of the Earth. But that definition only works here on Earth. The idea of falling using common everyday language as being in the direction of down does not work in places in the universe other than Earth. In space, somewhere between the Earth and it's moon, an object may fall to the earth or fall to the moon. At other places an object may fall towards the Sun or Jupiter. At other places in the universe an object may even fall to a point in space between stars and planets.
Falling using common everyday language is also true only due to gravity. What about an electrically charged object? A balloon rubbed on your hair and held close to the ceiling will fall up towards the ceiling. Electrically charged objects do not always fall due to the force of gravity, but due to electric forces. (Thank goodness or our electronics would not work and life would not even exist.) As masses fall in gravitational fields, charges or charged objects will fall to a place where they have less total potential energy. Magnetic objects will fall in a magnetic field to a place where they have less total potential energy.
Falling is a very common cause of people's injuries, possibly the most common cause. This is especially the case for elderly people, people with various conditions causing a loss of balance, and for people who do sports and other leisure activities requiring significant motion.
In many cases, elderly people become less steady on their feet and if they fall they are at a greater risk of having serious injuries, such as breaking their hip, because of the more brittle condition of their bones.
During sports and other recreational activities such as bicycling or skateboarding, people are more likely to fall. Some bicyclists and skateboarders wear protective clothing to protect their body in the event of a fall, such as a helmet, elbow pads, and knee pads.
Autumn
Autumn is the season after summer and before winter. In the United States this season is also called fall. In the Northern Hemisphere, it is often said to begin with the autumnal equinox in September and end with the winter solstice in December. In the Southern Hemisphere, it runs from the autumnal equinox in March to the winter solstice in June.