Why No One Has Measured The Speed Of Light

Summary

In this thought-provoking video, the host challenges the commonly accepted idea that light always travels at a constant speed. Through various experiments and thought experiments, the video explores the difficulties in measuring the one-way speed of light. While the round-trip speed of light is well-defined, no one has ever directly measured its one-way speed. The video discusses potential scenarios where light might travel differently in each direction and explores the implications for time, simultaneity, and relativity. It questions long-held assumptions in physics, suggesting that the nature of light and time might be more mysterious than we realize.

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Q & A

What is the speed of light, and how is it currently defined?

The speed of light is defined as exactly 299,792,458 meters per second. This definition was established in 1983, where the speed of light was used to define the length of a meter in terms of how far light travels in a vacuum in 1/299,792,458ths of a second.

Why can't we measure the speed of light in the same way we measure the speed of other objects?

Measuring the speed of light is different because, unlike other objects, we cannot directly track its motion using traditional methods. For example, using a timer to measure when light reaches a point is complicated by synchronization issues and the speed at which signals travel.

What was the problem with measuring the speed of light using two synchronized clocks?

The issue arises because, when moving, the clocks would no longer be synchronized due to the effects of special relativity, where moving clocks tick slower than stationary ones. This makes it impossible to measure the speed of light with just two synchronized clocks.

How did Hippolyte Fizeau measure the speed of light in 1849?

Fizeau used a spinning gear and a mirror positioned eight kilometers away. By adjusting the speed of the spinning gear, he measured when the reflected light passed through the next gap in the gear. This gave him an approximate value for the speed of light.

What is the difference between measuring the round trip and one-way speed of light?

The round trip speed of light has been measured by scientists, but the one-way speed remains unknown. The round trip is easier to measure because light travels to a point and then returns, whereas measuring the one-way speed is complicated by synchronization and relativity issues.

What is the 'Einstein synchronization convention'?

The Einstein synchronization convention is the idea that the time it takes for light to travel from one point to another is the same in both directions. This is a stipulation, not an experimentally verified fact, and serves as a way to synchronize clocks across different locations.

Why can't the one-way speed of light be measured directly?

The one-way speed of light cannot be directly measured because synchronizing clocks at different locations is inherently problematic. We need to know the one-way speed to synchronize clocks, but we also need synchronized clocks to measure the one-way speed, creating a circular problem.

What are the potential consequences if the speed of light is different in opposite directions?

If the speed of light differs in opposite directions, it could affect our understanding of simultaneity and cause issues with time synchronization across space. This could lead to discrepancies in how events are perceived to occur simultaneously, particularly in communication between distant locations like Earth and Mars.

What is the significance of the GPS system in relation to the speed of light?

The GPS system relies on the assumption that the speed of light is constant in all directions. If the speed of light were different in each direction, it would cause issues with the synchronization of satellite clocks, ultimately affecting the accuracy of the system.

Why is the concept of the one-way speed of light important in the context of general relativity and quantum mechanics?

The inability to measure the one-way speed of light presents a fascinating mystery in physics, which could provide insights into the deeper connections between space, time, general relativity, and quantum mechanics. It challenges the conventional understanding of simultaneity and could reveal new perspectives on the universe.