Exploring the Shapiro Delay: Is it Space or Time?

[Zman]

How is the Shapiro Delay interpreted in GR?
Is it that the curvature of space is increased around a massive body causing the path length to increase?
Or is it because time dilates making the speed of light appear to slow?
Or something else?

 

[MeJennifer]

The term delay in "Shapiro delay" is of questionable use. The light travel time simply increases when a massive or energetic source is near the travel path. If you use light travel time as a measure of distance (which I think is a very practical thing to do) you could say that distances increase between two points if a massive or energetic source is in the vicinity of the path between them.

 

[Entropia]

The Shapiro Delay is a phenomenon predicted by Einstein's theory of general relativity (GR) and has been observed in various experiments, such as the deflection of light by the Sun. It refers to the delay in the travel time of light as it passes through a gravitational field, such as that of a massive body like the Sun.

In GR, space and time are intertwined and are affected by the presence of mass and energy. The theory states that massive bodies, like the Sun, warp the fabric of space-time, creating a curvature that affects the path of light. This curvature is what causes the Shapiro Delay.

To understand this further, imagine a flat rubber sheet representing space-time. When a heavy object, like a bowling ball, is placed on the sheet, it creates a dip or curvature in the sheet. Similarly, a massive body like the Sun creates a curvature in space-time, and any object traveling through this curvature, including light, will follow a curved path.

Now, as light travels through this curved space-time, its path is bent or elongated, leading to a longer travel time. This is because the speed of light is constant, and it must travel a longer path due to the curvature of space-time. This explains why the Shapiro Delay is interpreted as a result of the increased curvature of space around a massive body.

It is essential to note that the Shapiro Delay is not due to the slowing down of light itself. In GR, time is also affected by the presence of mass, and it dilates or stretches as it approaches a massive body. This means that time appears to pass slower in a strong gravitational field, causing the perceived delay in the speed of light.

In conclusion, the Shapiro Delay is a result of the curvature of space-time caused by the presence of mass and energy. This curvature affects the path of light, leading to a longer travel time, and is not directly related to the slowing down of light or the dilation of time.