[runeks]

Admittedly -- and perhaps obviously -- I'm not a physicist. But as far as I can see, once we've defined length and time in terms of the speed of light, the speed of light is constant, by definition. The speed of light can never change after this, because it would be observed as all lengths/units of time changing.

Consciousness can't change either, because a change in consciousness changes everything that is experienced, so how can you know whether everything or consciousness changed? There's no difference.

Some terms can only be defined in terms of themselves. What's a meter? It's term used to describe a length of measurement equivalent to one meter. What's consciousness? It's a term used by certain life forms to describe what life is.

How can we study something that's always there, and when it isn't there we're not there either? Everyone "experiences" the absence of consciousness in deep sleep, and there's simply nothing there.

[Fjolsvith]

I have alluded in other places of the benefits of a meditative practice. One I have experienced is being "awake" in my dreams. Having a continuous stream of consciousness through my nights of sleep.

I am able to control my actions during and the outcomes of the situations I dream about, and fully recall them after waking.

[thriftwy]

You're asking "how can we study" all the time.

But if there was a clear answer to that question, it won't be science.

Science is figuring out how to study things that we could not study previously.

[euyyn]

But we also use the speed of light to define other units after we found out, by experiment, that it was indeed constant.

[DonaldFisk]

It was inevitable that it was measured to be constant. You need to build a measuring apparatus out of physical matter and use its physical properties to measure things. Use of any reasonable measuring apparatus will have the built-in assumption that c and h are constant, and either particle masses or G is constant, allowing you to measure combinations of lengths, times, and masses.

[euyyn]

> Use of any reasonable measuring apparatus will have the built-in assumption that c and h are constant

The speed of light was measured constant by the famous Michelson-Morley experiment, whose apparatus didn't have any built-in assumption about c (nor had anything to do with h).

[DonaldFisk]

The Michelson-Morley Experiment showed that light velocity had the same magnitude in different directions.

One metre is defined to be the length of the path travelled by light in a vacuum in 1/299 792 458 seconds. Therefore, c = 299 792 458 metres per second. The second is defined in terms of the frequency of electromagnetic radiation emitted during a transition between two specific states in a caesium atom. In other words, it's a unit of time as measured on a kind of atomic clock, which by convention is constant.

It's an open question whether a second on a pendulum clock is the same as one measured on an atomic clock for all time, as that depends on G.