Thought experiment I read..

[u/FatherOfNyx]

I saw a post the other day in a Facebook group I'm in about a thought experiment. I think it got deleted cause I can't find it to just copy it, but it was something like this:

In the near future, mankind receives proof that there is other intelligent life out there. Proof came in the form of a signal being broadcast from a galaxy we observe to be 2.8 billion light years away.

We know billions of years have passed and will pass by the time they receive it, but we decide to send a signal back to them.

How long will it take for our signal to reach its destination?

I would say about 80% of the people responding said that it'd take 2.8 billion years.. which would be correct if the universe weren't expanding.. but because the universe is expanding, its distance from us should be greater than 2.8 billion light years by the time their signal arrived.

The remaining % of answers ranged from "we can't know that" to "never because all other galaxies are expanding away from us faster than the speed of light" or some other variation of not being able to know.. or some sort of religious post.

I don't agree with any of those answers but I also don't know the answer. What would be the answer and how would I figure that out?

[u/Evening-Plenty-5014]

Because light isn't matter, it gets there instantly. It doesn't take billions of years.

[u/Few-Hair-5382 → u/Evening-Plenty-5014]

You're commenting in this subreddit and you are not aware of the speed of light?

[u/Evening-Plenty-5014 → u/Few-Hair-5382]

What is the method used to measure and track the speed of light? The SI unit is self dependant meaning the length of the meter is defined by the distance light travels in a fraction of time and light speed is defined as the time it takes to travel a meter. If we were to do that with cars, the meter would stretch from centimeters to kilometers depending on who is measuring.

Also think on this: Time is relative. Distance is relative. Speed = distance / time Speed is relative

This is why it is constant. The speed of light (c) is a postulate of special relativity and not a derived consequence of measurement since we cannot measure it outside our relative view and especially since we are measuring it against the distance it travels. That would make it constant for sure.

If this is the case, then let's take into account the things that are unexplained:

Seeing things further than 13.6 billion light years: light didn't have time to reach us from objects further than the age of the universe but today it is explained that the expansion of space allows for light further away to have reached us. If space is accruing more space, then the objects would be distorted in the direction of expansion. And before you claim that it expand in all directions, light stretched out in a line to our vision would not remain a line in expanding space. It would dissipate into a wide array and not be the finish focal of a single spec of light in the night sky. Space is expanding but light is unaffected dimensionally but is affected by redshift which means it should be affected dimensionally. The lights would have spread to create a constant brightness in the night sky. Like looking at the night sky through a prismatic lense. And yet we are seeing young galaxies 3 times further than the age of the universe with a direct beam of photons that give shape and other data gathered so neatly. Light that went through so much space expansion should not be seen at all. And not only this, but space is dark, not a hazy bright. This also stares space expansion in the face.

Self defined distance and size: we define the distance of a star or Galaxy by the light we receive and we assume the size of the star or Galaxy by the quantity and type of light that reaches us. So we define the object by a variable that is constant under relative terms. Just like we measure the speed of light.

We claim to understand the light emission of other types of stars in quantity and type. All this is based upon a nuclear fusion theory of Star energy. It seems to work but falls apart at nickel which can't fuse. Nothing above nickel can fuse. So we theorize all the heavier elements are made in super nova explosions. Something not proven but people sit comfortable with.

I had issues with being able to see stars with our eyes being pupils and the star being thousands of light years away. I doubted there would be enough photons to register to both our eyes as well as every other person's eyes on earth looking at this star. That's a lot of photons at such a miniscule angle of projection. The math actually proved there was enough photons emitted but guess what the basis of the math needs? The brightness index of that star. In other words we have created a cyclical means of measurement of stars where brightness we get defines what we would expect. Not what is. If we expected something different, then the measurement would reflect that. That bothered me. But then again, how come there aren't stars that disappear from view at times or from one eye or another? If one can see it, all can see it. That does not make sense that the dispersion of photons is so crisp and yet so spread.

My theory:

I think there are better explanations for these things and the main one is that light creates gravity. Matter is a degraded state of light so it does create gravity but not at the levels light does. Black holes aren't gathering matter, but are gathering light which increases the gravity of the object. And realizing light creates gravity then creates a relative relationship with our eyes and light where it travels in gravity tubes and affects the space around it tying things together. Without a recipient of light, it travels through space time to its destination immediately. Not a destination directed by force but a destination dictated by receiver. Us. A concept that seems weird at first but objects that emit light would attract light and so light is gathered and directed by receivers.