# Trying to make sense of the time in spacetime

• WarrickF
In summary, the concept of spacetime was not new with Einstein's theory of relativity, but it became essential in his theory. Spacetime is a graph with position and time as its axes, where each point represents a unique event. This idea can be better understood through the book "General Relativity from A to B" by Robert Geroch.
WarrickF
trying to make sense of the "time" in spacetime

Hi All,

I'm trying to make sense of the "time" in spacetime. I understand that Einstein chaned the way of thinking to object following a path in space time, and that matter bends space time but I really don't unserstand where the time part in space time comes from. Can someone please help me out here?

Thanks
Warrick

WarrickF,

The notion of spacetime was not new with Einstein's theory of relativity. It is perfectly consistent with the classical relativity postulated by Galileo, incoroporated by Newton into his laws of motion, and generally believed until 1905. But in classical relativity, it's optional; in Einstein's relativity it's essential; at high relative speedsyou can't consider location and time independently.

That said, however, the idea of spacetime isn't at all complicated. Imagine (or draw) a graph with position along the horizontal axis and time along the vertical axis. Every point on this graph is associated with a unique time and a unique location, right? These points represent events, which are occurences (like a flash of light or a snap of your fingers) at some place and at some time. This graph represents spacetime. Everything that's ever happened, is happening, or ever will happen is somewhere on this graph.

There's a great little book that develops the theory of relativity with almost no math by using the notion of events in spacetime. It's by Robert Geroch, and I believe the title is "General Relativity from A to B" or something like that. It's a great read, and you'll definitely come away understanding spacetime.

## 1. What is the concept of spacetime?

Spacetime is a mathematical model that combines the three dimensions of space and the dimension of time into a single four-dimensional continuum. It is used to describe the physical universe and the relationship between space and time.

## 2. How does spacetime affect the passage of time?

According to the theory of relativity, spacetime is not static and can be influenced by gravity and velocity. This, in turn, affects the passage of time. Objects in a strong gravitational field or moving at high speeds experience time differently than objects in a weaker gravitational field or at rest.

## 3. Can we travel through spacetime?

While we cannot physically travel through spacetime as a whole, we can travel through different points in spacetime. This is the basis of time travel theories, where one can potentially travel back or forward in time by manipulating their position in spacetime.

## 4. How do we measure time in spacetime?

In spacetime, time is measured in units called "spacetime intervals". These intervals take into account both space and time and are calculated using the speed of light as a constant. This allows us to measure time in a consistent manner, regardless of an observer's frame of reference.

## 5. What are the implications of understanding spacetime?

Understanding spacetime has had a significant impact on our understanding of the universe and has led to groundbreaking theories such as the theory of relativity and quantum mechanics. It also has practical applications, such as in GPS technology, where precise timing is necessary to accurately determine location.

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