# Is proper time Lorentz invariant?

If the appropriate time is Lorentz invariant, then the proper time is also Lorentz invariant. The right time period between the same two occurrences is agreed upon by all observers in all inertial frames. Thus, if one observer measures a shorter time interval than another observer, they are simply observing different events. There is no need for either observer to be correct or incorrect.

In special relativity, there is no such thing as "the" universal time reference. Instead, there are many possible references systems, with different advantages and disadvantages. One system that has been used frequently is called "coordinate time". In coordinate time, the passage of time is inferred from changes in the positions of physical objects. If object A is located at a certain position at some time t0, and at a later time t1 it is found to be located at a new position B, the distance AB is found to be equal to ct1-ct0. Where c is the speed of light in vacuo.

It can be shown that if you follow an event as it passes you will find that the amount of coordinate time elapsed between your observation of that event and any other observation made by someone else is the same for you both. This means that the coordinate time between any two events is always the same for all observers, and thus it is said to be "Lorentz invariant".

## What is the proper time in relativity?

Proper time along a timelike world line is defined in relativity as the time recorded by a clock following that line. Because proper time is only fixed up to an arbitrary additive constant, meaning the setting of the clock at some event along the world line, this interval is the quantity of interest. It is important to note that because proper time is defined relative to some reference frame, it can be measured only within certain limits: either the object being observed is moving with respect to the reference frame or there is some other well-defined standard by which relative times can be established.

In general relativity, where gravity plays a role, there are two different definitions of proper time. The first definition is identical to that given above for non-gravitational theories. It is important to remember that although both definitions give the same result for any single event, they may not give the same result when integrated over time. For example, if we let $\tau$ be proper time as defined by Einstein's equation and $t$ be ordinary time, then the integral $\int d\tau = \int dt$ does not necessarily hold; instead, we have $\Delta\tau = \Delta t(1 - \frac{v^2}{c^2})$, where $v$ is the speed of the particle with respect to the reference frame used to define $\tau$.

## What is the proper time in time dilation?

According to the Lorentz transformation, a clock in a moving frame appears to be running slowly, or "dilated." The time will always be the shortest when measured in its rest frame. The "proper time" is the time measured in the frame in which the clock is at rest. For example, if a clock on a train moved with constant velocity along with the track, it would appear to run more slowly than clocks not on the train and would thus call into question our understanding of time itself.

In reality, there is no such thing as "absolute time." Rather, time is defined by human observers as the flow of time elapses between any two events that can be observed. Thus, depending on how you observe them, objects may appear to flow past one another quickly or slowly relative to each other. A perfect example of this is given by special relativity: If you are on board a moving ship, the people on shore will think that you have gone for many years without aging because they will see you still looking young. You would feel no difference between being on board the moving ship and being at home because you are observing things from an outside perspective; but someone who is born on board the ship and grows up there would seem to go back in time as they get older compared to people on land who would still appear the same age as when they were younger.

This has important implications for those who believe in eternal life after death.

## Is time relative to the observer?

Time isn't related to the observer, no. But what you observe is affected by your location and movement. For example, if you are standing on a hill, then you will notice that people appear to move more quickly when you are walking down the hill toward them.

This effect explains why friends and family who live far away seem to disappear off of our phones without so much as a good-bye email or text. Their time appears to be running out while we're still talking or texting with them!

People also say that time passes faster when you are having a good day and getting a lot done. When you are struggling with life's challenges, time seems to drag on forever.

The passage of time is subjective, depending on how you feel about things. If you are having a bad day, you'll want to rush through it so you can get home to your phone and shut it out again for a few days. But if you are having a good day, you'll want to soak in every minute of it.

Time is just a tool used by humans to keep track of events that happen over time.

## What are continuous time systems?

A continuous-time system is time-invariant if, for every input with a corresponding output y (t) = S x (t), the output corresponding to a shifted input x (t t) equals the original output y (t t) = S [x (t)] (delayed or advanced). In other words, if you plot y (t) against x (t), the graph will be a straight line with a slope of S and an intercept of 0.

Time-variant systems are not continuous time; instead, they're discrete time systems. A discrete-time system is time-variant if, for some inputs x (t), the output does not equal the same value as the output for the same input at a later time point. Otherwise stated, a discrete-time system is time-variant if y (t) does not equal y (t + 1).

In practice, we usually can't build true continuous-time systems. Instead, we use approximation methods to achieve effects that look like continuity. For example, low-pass filters used in audio applications approximate a continuous-time signal by averaging together multiple samples of it taken at different times. This method works well for signals that vary slowly with time, such as music played back from a CD player. It doesn't work so well for signals that change rapidly, such as voice waves. In this case, the filter needs to be designed specifically for the signal it's approximating.

##### Lola Griffin

Lola Griffin is a spiritual healer who has been helping others for over 20 years. She has helped people with things such as anxiety, depression, and PTSD. Lola believes that we are all connected and that we can heal ourselves by healing others.

#### Disclaimer

SpiritualWander.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.