Can the Speed of light change?

I have read in various places that the Speed of Light can change. If so, how do we know the light still shows an old universe? I am also doing a project on the origin of life in biology so this would be helpful to support an old Universe.


The comment about changes in the speed of light almost always refers to how fast light travels THROUGH light-permeable substances (medium in the singular, media in the plural).

At this link there is a Physics page on the subject…


Some physicists like to say the Speed of Light is not really about the properties of light. It’s really about the “Speed of Causation”!

From the Photon’s point of view, it experiences no time, and it is simultaneously at the beginning of its creation, and at the end of it’s trip (in your eye, or hitting a blade of grass).

It’s existence could be said to incorporate a single point in the Tenth Dimension (if you are not including the 4th dimension of time), or all of the Eleventh Dimension (if you are including the 4th dimension of spatial time).

And that as you unpack this highest dimension, that single point starts to stretch out in the eyes and minds of the beings confined to these lower dimensions, where consciousness or awareness experiences the illusion of time one planck moment at a time.

Hi DarkX :slight_smile: ,

This is a great question that has been studied carefully by many physicists. It turns out that the speed of light in vacuum cannot change for a very fundamental reason, namely because light consists of electromagnetic waves. It can be proven from Maxwell’s equations that such waves travel with a constant speed. I’ve written a post on this for BioLogos:

On top of that, we are able to confirm in many independent ways that the speed of light (the value of c) does not change in the universe.

One way to show this is by looking at the famous equation of Einstein: E = mc^2 in the context of stars. Inside stars, hydrogen atoms are being fused to form helium atoms. Based on the mass difference between the ingredients and the final product, Einstein’s theory tells us how much energy is released in this process (see this link for a more elaborate explanation). This energy (E) depends directly on the speed of light (the constant c in Einstein’s equation). If the speed of light would change across space or time, the stars in our universe would not be able to remain stable as they are.

Hope that is helpful for you. Let me know if you have any questions!


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@Casper… aren’t you the clever one!

The problem is that one you move text OUT, it is no longer available for the search tool.

… But you folks call the shots…