Space like time like light like separations?

• Baggio
In summary, the conversation discusses different types of separations in spacetime, specifically lightlike, timelike, and spacelike. Lightlike separations occur when a light signal reaches a specific location at a specific time. Timelike separations happen when events occur in a specific order for all observers. Spacelike separations occur when events are not causally connected and can have different temporal orders for different observers. The conversation also briefly touches on the concept of quantum electrodynamics and its role in spacelike connectivity.
Baggio
Hi

I tried using the search function but it keeps timing out on me. Anyway I'm trying to find a good description of what is meant by space/time/light like separations, could someone help me out?

Thanks

Consider two locations in spacetime, say (t1,x1) and (t2,x2) where the ts are time coordinates and the x's are space coordinated (you can think of them either as one dimensional numbers or as three-dimensional vectors). Suppose you send a light signal out from (t1,x1). There are three possibilities:
1) The light arrives at space location x2 precisely at time t2. Then the two four-dimensional locations are said to be lightlike separated. An example; if you see a star, then the star and your eye are lightlike separated.
2) The light arrives at x2 before t2. Then (t1,x1) and (t2,x2) are timelike separated, and we say that (t2,x2) is inside the lightcone of (t1,x1). Timelike events can interact, since even a slower-than-light cause can reach x2 from x1 in time (t2-t1).
3) The light arrives at x2 after t2. Then (t1x1) and (t2,x2) are spacelike separated and cannot causally interact, since a causal influence would have to travel faster than ligh (impossible for real causes) to get from x1 to x2 in time (t2-t1).

Thanks that helped!

Just want to thanks selfAdjoint for your simple but great descriptions.

Just thought I would add that timelike separated events always happen in the same order according to any inertial observer (to conserve causality), while different observers with different relative velocities can disagree on the temporal order of spacelike events, but this is not a problem because spacelike events are not causally connected.

yuiop said:
Just thought I would add that timelike separated events always happen in the same order according to any inertial observer (to conserve causality), while different observers with different relative velocities can disagree on the temporal order of spacelike events, but this is not a problem because spacelike events are not causally connected.

Jumping between the quantum physics folders and the relativity folder is like jumping from one multiple personality disorder to another.

In quantum electrodynamics, spacelike connectivity is a requirement.

Space like separations are events always separated in space for every frame.

Time like spearations are events always separated in time for every frame.

1. What is the concept of "Space like time like light like separations"?

"Space like time like light like separations" is a term used in physics to describe the distance between two events in space and time, taking into account the speed of light. It takes into consideration the fact that the speed of light is constant and is the maximum possible speed at which information can travel.

2. How is the concept of "Space like time like light like separations" related to the theory of relativity?

The theory of relativity, proposed by Albert Einstein, states that the laws of physics are the same for all observers in uniform motion. This includes the concept of "Space like time like light like separations" which is used to calculate the distance between two events in space and time, taking into account the constant speed of light.

3. How is "Space like time like light like separations" used in astronomy?

In astronomy, the concept of "Space like time like light like separations" is used to determine the distance between celestial objects. This is done by measuring the time it takes for light to travel from one object to another. By using the speed of light and the time it takes for light to travel, the distance between objects can be calculated.

4. Can "Space like time like light like separations" be used to travel through time?

No, "Space like time like light like separations" does not allow for time travel. It is simply a mathematical concept used to describe the distance between events in space and time. However, the theory of relativity does allow for the possibility of time dilation, where time can appear to pass differently for different observers.

5. How does the concept of "Space like time like light like separations" impact our understanding of the universe?

The concept of "Space like time like light like separations" is crucial in understanding the structure and behavior of the universe. It allows us to accurately measure distances between celestial objects and to understand the effects of gravity and motion on space and time. Without this concept, our understanding of the universe would be limited and incomplete.

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