The time extension refers to the seemingly strange fact that time passes at different rates to different observers depending on their relative motion or position in the gravitational field.

This is how it works. Time is relative. As intuitive as it sounds, it is a consequence of Einstein theory of relativity . In everyday life, we are used to the fact that speed is relative – so a car traveling at 60 mph (97 km / h) relative to a stationary observer, for example, would be considered to be moving at 120 mph (193 km / h) in the opposite direction.

The same phenomenon also affects time. Depending on the relative motion or position of the observer in the gravitational field, that observer would experience time passing at a different speed than the other observation. This effect, known as time extension, is only noticeable under certain conditions, although at a low level we are subject to it all the time. Let’s take a closer look at time extension theory and some of its implications, including GPS errors and the famous double paradox.

Time extension defined
Time dilation is slowing down time as perceived by one observer relative to another, depending on their relative motion or position in the gravitational field. It is the result of Einstein’s theory of relativity, in which time is not as absolute as it may seem; the speed at which it travels is different for observers in a different frame of reference.

According to a late professor of physics at Michigan State University, Einstein’s starting point was the fact that light always has the same measured velocity regardless of the observer’s own motion. Jon Pumplin . This seemingly innocuous assumption inevitably leads to the conclusion that “clocks move slowly.” This phrase is often used as a concise description of the expansion of time, but it is somewhat misleading because it highlights clocks that are only relevant if we use them to measure time. But we should really think of the dilatation of time as “an unexpected truth about space and time, not a feature of the clock,” Pumplin argued.

Time extension and speed of light
The Space Shuttle Discovery rises from the Kennedy Space Center as spectators watch on July 26, 2005 in Titusville, Florida. Shuttle crew members would have experienced an expansion of time and would therefore have seen the journey take less time than the country’s residents. (Image credit: Mario Tama / Getty Images)
There are two parts to the theory of relativity – a special theory of relativity and a general theory of relativity – and time extension features in both. The principle that speed of light is the same for all observers, it plays a key role in a particular theory of proportionality. According to a physicist at Boston University, one of its consequences Andrew Duffy , means that two observers moving at a constant speed measure different times between the same events. But the effect becomes perceptible only at speeds approaching the speed of light that is generally symbolized c .

Imagine a spaceship flying at 95% light speed to a planet 9.5 light-years away. An observer stationary on Earth measures travel time divided by speed, ie 9.5 / 0.95 = 10 years. Spacecraft crew members, on the other hand, experience time dilatation and see the voyage lasting only 3.12 years. (The math is a little more complicated here, but we’ll get back to that later.) In other words, between leaving the country and reaching their destination, crew members age a little over three years, compared to people 10 years ago. The globe.

While truly striking situations like this require tremendous speeds, time expansion occurs more modestly in any relative motion. For example, an ordinary pilot who crosses the Atlantic every week would have experienced about a thousandth of a second less time than a non-passenger after 40 years, says “How to Build a Time Machine | “(St. Martin’s Griffin, 2013). The book also explains how in the real world the speeds needed for more impressive time extensions, at least for short-lived elemental particles called food. These are created when cosmic rays hit the Earth’s upper atmosphere and can travel at almost the speed of light. The moons are so unstable that they shouldn’t take long enough to reach the surface of the Earth, but many of them are. This is because an extension of time can extend their lifespan by a factor of five.

Time dilation and gravity
Ten years after Einstein had assumed a special theory of relativity, he expanded his theory to include gravitational effects. general theory of relativity . But the time extension in this theory does not depend on the speed of travel but on the strength of the local gravitational field. We already live in a moderate gravitational field on the Earth’s surface, so it turns out that we are subject to the dilatation of time without noticing it. In addition, the intensity of the effect varies as we move up and down the Earth’s field.

Gravity is slightly weaker on the top floor of a tall building than at ground level, so the time – extending effect is also weaker at higher levels. Time goes on the farther you are from the surface of the earth. Although the effect is too small to be perceived by the human senses, the time difference between different altitudes can be measured with very accurate clocks, as described by Christopher Baird, a professor of physics at West Texas A&M University. website .

To see a more dramatic example of the expansion of gravitational time, we need to find a place with a much stronger gravity than the Earth, such as a black hole environment. NASA has wondered what would happen if the clock were placed in orbit 6 miles (10 kilometers) a black hole having the same mass as the sun. It turns out that looking through a telescope from a safe distance to display the clock would take about an hour and 10 minutes.

Time dilation equation
(Image credit: Shutterstock)
Einstein’s original time dilation equation is based on a special theory of relativity. As scary as the equation looks at first glance, it’s not that difficult if we have a scientific calculator and work out the formula step by step. Take the speed first v moving object and divide it by c , the speed of light and squares the result. This should give you a number somewhere between 0 and 1. Subtract this from the number 1 and take the square root; then flip the result. You must leave a number greater than 1, which is the ratio of the time interval measured by the stationary observer to the time interval measured by the mobile observer.

If that sounds like too much work, you can use online calculator provided by Georgia State University. Just enter the speed, v , as a fraction c , and the corresponding time ratio is automatically displayed. The same website also has an analog formula related to gravitational time dilation.

Expansion of time in space
Given the expansion of time and gravity, the launch of the Voyager 1 in 1977 turns out to be 1.2 seconds younger than the country’s inhabitants. (Image credit: NASA / JPL)
Time extension has a double significance for spacecraft due to both their high velocities and the changing gravitational fields they experience. In 2020, a group of students at University of Leicester In the United Kingdom, the time-extending effects of NASA’s Voyager 1 spacecraft were calculated over the 43 years following its launch in 1977. Special relativity predicted that Voyager would age 2.2 seconds less than we have on earth. But the general theory of relativity partially balances this. We are experiencing a stronger gravity than a spacecraft, so in that sense, the sonar is about 1 second more obsolete than we are. Combining these two effects, Voyager still turns out to be younger than Earthlings, but only about 1.2 seconds.

Such calculations may seem pointless, but they can be very important in situations where accurate timing is critical. In the case of GPS satellites For example, when used for navigation, timing errors of only a few nanoseconds (parts per billion) can result in a positioning error of hundreds of meters, which is clearly unacceptable if you try to specify a specific address. To achieve the desired accuracy, the GPS system must take into account the time extension, which can be 38 microseconds (parts per million) per day. Richard W. Pogge , Distinguished Professor of Astronomy at Ohio State University. As in the Voyager example, both special and general relativity contribute to this figure, as 45 microseconds comes from the dilatation of gravitational time and minus 7 microseconds from the velocity-related effect.

Double paradox
One of the most shocking consequences of the expansion of time is the so-called double paradox. In this thought experiment, one identical twin lives on earth as their twin travels back and forth to a distant star at speeds approaching the speed of light. When they meet again, the traveling twin is – thanks to the expansion of a special relativistic time – much less elderly than the one who stayed home. The apparent “paradox” stems from the erroneous belief that the situation is symmetrical – in other words, one could also say that the traveling twin is in place relative to the Earth-bound twin, meaning that the Earth’s inhabitant would be less old than the star-traveling twin. . .

But this is not the case because the situation is not symmetrical. When a special theory of relativity speaks of relative motion, it means motion at steady speed in a straight line . That is not the case here. Since the twins are together at the beginning and end of the journey, the passenger must accelerate from a stop to a top speed and then at some point turn around and head back in the opposite direction before finally slowing down to a stop again. These phases of acceleration and deceleration bring out the general theory of relativity because they have similar effects as in the field of gravity, says “Paradox: The nine greatest puzzles in physics “(Crown, 2012). Once mathematics has been developed to account for this acceleration, it turns out that somewhere time travel , the twin moving in space travel is indeed aging more slowly than that bound to Earth.

Resources that extend extra time
Originally published on Live Science .