# Speed of light and universal expansion.

• thewiseman
In summary, the conversation touches upon the evidence for the expansion of the universe through the red-shift/Doppler effect, the constant speed of light, and the maximum speed of an object. The possibility of the red-shift being caused by other factors and the reasoning behind the constant speed of light are discussed, as well as the theoretical concept of exceeding the speed of light and its implications. The conversation ends with the acknowledgement that there may not be a definitive answer for why the speed of light is constant and at its specific value.
thewiseman
The biggest chunk of evidence for expansion of the universe is the whole red-shift/Doppler effect deal, saying that as something that emits light while traveling away from the observer, the wavelength of the light will be "stretched" making it appear red. There is one thing I'm wondering. Could the red shift be caused by something else, like long distances perhaps. Maybe over the course of hundreds of thousands of light years, the wavelength of the light lengthens, due to maybe extremely long distances, or maybe a long term effect of the pull of gravity on the light. Does this sound reasonable, or are there any other ways it could happen?

Also, it is theorized that the speed of light is constant. I'm not doubting this yet, but can anyone tell me what this is based on? If it turned out to be false, I'm sure that many theories of science in general would have to change, and that fact itself might uphold its truth, but what is it based on? Is there any experimental evidence on this?

My last question is: why is the speed of light constant, why is it at that speed, and why is that the maximum speed of an object? Surely, there would be some geometrical way to exceed that speed, even if the methods seem unreasonable. For example, if one were to take a pole, say one light-year long, and swing it around at a speed in which it would complete one radian in one year, then the end of the pole would be traveling at the speed of light, so what if it was swung faster? Theoretically, anyway, I'm hoping not to get responses on how that is impossible, I'm just asking what would happen? What would happen to the end of the pole, where the speed of light is exceeded?

Thank You.

thewiseman said:
The biggest chunk of evidence for expansion of the universe is the whole red-shift/Doppler effect deal, saying that as something that emits light while traveling away from the observer, the wavelength of the light will be "stretched" making it appear red. There is one thing I'm wondering. Could the red shift be caused by something else, like long distances perhaps. Maybe over the course of hundreds of thousands of light years, the wavelength of the light lengthens, due to maybe
extremely long distances, or maybe a long term effect of the pull of gravity on the light. Does this sound reasonable, or are there any other ways it could happen?

Broadly the idea you refer to is 'tired light', the concept that light loses energy by a myriad of proposed mechanisms as it travels. This has shown to be inconsistent with observations, particularly the fact that it does not explain cosmic time dilation.

thewiseman said:
Also, it is theorized that the speed of light is constant. I'm not doubting this yet, but can anyone tell me what this is based on? If it turned out to be false, I'm sure that many theories of science in general would have to change, and that fact itself might uphold its truth, but what is it based on? Is there any experimental evidence on this?

Relativity (both special and general) a founded on the idea that light travels at a constant speed for all observers. This has been verified countless times by many different experiments. If you've ever used a GPS you are relying on correction terms that depend on SR, and hence the constancy of light, to be correct. Why do you doubt that the speed of light is constant?

thewiseman said:
My last question is: why is the speed of light constant, why is it at that speed, and why is that the maximum speed of an object?

The speed of light is determined by the inverse square root of two other constants relating to how electric and magnetic fields propagate through a vaccum. This comes about from Maxwells equations of which light is a wave like solution. Why these constants have their specific values is not known. At present we can determine them by experiment only, but perhaps in the future we may have a theory that predicts they should have the values that they do for some other more fundamental reason. Perhaps they are just those values because that's what they happen to be in our universe.

thewiseman said:
Surely, there would be some geometrical way to exceed that speed, even if the methods seem unreasonable. For example, if one were to take a pole, say one light-year long, and swing it around at a speed in which it would complete one radian in one year, then the end of the pole would be traveling at the speed of light, so what if it was swung faster? Theoretically, anyway, I'm hoping not to get responses on how that is impossible, I'm just asking what would happen? What would happen to the end of the pole, where the speed of light is exceeded?

Thank You.

Unfortunately if your question makes no sense then the answers cannot either Since our current theories do not permit faster than light travel it is impossible to meaningfully say what they predict would happen if you did break that speed... It's like asking how 1+1=3, but not allowing the response that it simply does not!

If you did find a 1 light year long pole and attempted to swing it faster than 1 radian per year you would find that you would need to supply an infinite amount of force in order to do so.

Thanks.

I wasn't doubting that the speed of light is constant, I actually said I don't yet, meaning that if no one had a reason for it then I would.

Otherwise, it was very helpul. Thank you.

Ah yes I misread you post slightly, sorry! I hope you continue not to doubt it (within the healthy level of doubt everyone should have about every idea).

Cheers

## 1. What is the speed of light?

The speed of light is a physical constant that represents the speed at which light travels in a vacuum. It is approximately 299,792,458 meters per second (or about 670,616,629 miles per hour).

## 2. How is the speed of light measured?

The speed of light is typically measured using a variety of methods, including using lasers, interferometers, and astronomical observations. One of the most accurate methods is using a device called a cavity resonator, which measures the time it takes for light to travel back and forth between two mirrors.

## 3. Can anything travel faster than the speed of light?

According to Einstein's theory of relativity, the speed of light is the maximum speed at which any object can travel. This means that nothing can travel faster than the speed of light in a vacuum.

## 4. How does the speed of light relate to universal expansion?

The speed of light plays a crucial role in our understanding of the expansion of the universe. According to the theory of general relativity, the speed of light is a fundamental constant that determines the maximum speed at which information can travel through space-time. This means that the expansion of the universe is limited by the speed of light.

## 5. Can the speed of light change?

Current scientific evidence suggests that the speed of light is a constant and does not change. However, some theories, such as string theory, propose the existence of extra dimensions that could potentially affect the speed of light. These theories are still being studied and have not been proven.

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