We cannot measure the speed of light

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Discussion Overview

The discussion centers around the measurement of the speed of light, particularly in relation to the concept of space and its expansion. Participants explore whether the speed of light can be measured in a vacuum or only in the context of expanding space, and whether this has implications for the constancy of the speed of light over time.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants propose that the speed of light cannot be measured in a vacuum but only in space, suggesting that the expansion of space could imply a variation in the speed of light over time.
  • Others argue that the speed of light is measured locally and that expanding space does not affect this measurement, using analogies such as a snail on a stretching elastic band to illustrate their point.
  • There is a contention regarding the definition of "space" and "vacuum," with some participants questioning how a vacuum can be considered separate from space.
  • One participant asserts that since speed measurements inherently require space, it is unclear if the speed of light is dependent on the nature of space, suggesting a belief that space is not truly a vacuum and may be expanding in a way that affects its density.
  • Another participant challenges this view, stating that the speed of light can be measured in a laboratory setting without needing "outer space," emphasizing that the distance between measuring equipment is sufficient.
  • Some participants note that in cosmology, the speed of light can appear to vary due to the expansion of space, which complicates the understanding of light travel over vast distances.
  • There is a mention of the geometrical nature of space expansion, with a participant suggesting that the current understanding does not support the idea of new space emerging or density changes in space.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the measurement of the speed of light and its relationship with space. There is no consensus on whether the speed of light is dependent on the nature of space or how it should be measured.

Contextual Notes

Some limitations in the discussion include unresolved definitions of "space" and "vacuum," as well as differing interpretations of how the expansion of space affects measurements of light speed. The discussion also reflects varying levels of understanding regarding cosmological principles.

willigee
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we cannot measure the speed of light in a vacuum only in space, and since we are told that space is expanding it could be that the speed light varies through time.
 
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Wait, what?
 
willigee said:
since we are told that space is expanding it could be that the speed light varies through time.

We measure the speed of light locally, so that expanding space doesn't affect the speed of light although it may, while the light is in flight, move around the endpoints of the light's journey.

There's an analogy that you'll see sometimes: Imagine a snail crawling along an elastic band that we're stretching. There's no question about what the speed of the snail is relative to the rubber underneath it, and stretching the rubber doesn't change that speed. However, depending on where the snail started and how quickly we're stretching the rubber, the time it takes the snail to get from point A to point B may not have much to do with the distance between A and B at any particular moment.
 
willigee said:
we cannot measure the speed of light in a vacuum only in space,


Mmmmm... How is a vacuum (aka "empty space") not space? In any case, we measure the speed of light by look at the relationship between the emission and detection of light signals (and there are some important subtleties about the difference between one-way and round-trip measurements).
 
I am saying that since we cannot measure the speed of light without space we do not know if the speed is dependent on it. I believe that space something, not a vacuum in the true sense of the word, and if it is expanding it is either becoming less "dense" or more space is coming from somewhere to maintain the "density".
 
willigee said:
I am saying that since we cannot measure the speed of light without space we do not know if the speed is dependent on it.

:confused: Can you measure any speed at all without space? What does "meters/second" mean?
 
willigee said:
I am saying that since we cannot measure the speed of light without space we do not know if the speed is dependent on it. I believe that space something, not a vacuum in the true sense of the word, and if it is expanding it is either becoming less "dense" or more space is coming from somewhere to maintain the "density".

I think you are referring to space as in outer space ?

this is not correct, as others have been trying to tell you :wink:
You are still holding onto a mistaken belief

just google "how to measure the speed of light"
there's hundreds of references for you to read.

Speed of light can easily be measured in a laboratory with the appropriate equip.
You don't need outer space. The ONLY "space" you need is a distance between the measuring equip.

Dave
 
willigee said:
I am saying that since we cannot measure the speed of light without space we do not know if the speed is dependent on it.

Well, depending on what you mean by "speed", it is dependent on space. In cosmology there are multiple ways to define the speed of something since expansion is moving things away from us. The speed of light "through" space appears to be c at all times, where c is approximately 300,000 km/s. However, the expansion of space can make it appear that light is traveling slower than it really is over very very long distances or time. For example, one might expect light emitted 1 billion light years from us to take 1 billion years to reach us. However, the expansion of space actually causes it to take much longer. (I don't know exactly how much longer)

I believe that space something, not a vacuum in the true sense of the word, and if it is expanding it is either becoming less "dense" or more space is coming from somewhere to maintain the "density".

While you may believe whatever you want, it may help to realize that our best understanding of the expansion of space is that it is geometrical in nature and does not involve "new" space coming from somewhere or that space is becoming less dense. Note that this is built off of real, modern observations and math, and it fits all observations extremely accurately.
 
Closed, pending moderation.

Zz.
 

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