It’s an established, working theory in Astronomy, that the Universe is approximately 12 billion years old, well, maybe 13. At the same time, Astronomers have been able to observe distant objects in the Universe, far beyond our own galaxy and most others, the light of which has taken 13 billion years or so to reach us. And as the linked article suggests, there is an issue around how Astronomers claim to know this. And so a key phenomenon which takes place, is called The Doppler Effect, which is akin to how the sound of a car on the highway seems higher in pitch when it’s moving towards us, but drops down in pitch as it passes us. This phenomenon also takes place with Light.
If the light of a distant object is in fact red-shifted, then a natural conclusion which Astronomers might come to, is that this must be due, to the Doppler Effect. Alternative hypotheses which have been proposed included ‘Tired Light’, the idea that light just gets tired as it travels through space, and loses photon energy. The Tired Light hypothesis is presently defunct.
But there could be another way to explain why, the light from such a distant object is red-shifted. If the light took 13 billion years to reach us, this might really just mean, that those objects were 2.9 billion light-years away from us, when they emitted the light which we observe today. In the 13 billion years that followed, those objects can easily have moved further away from us. How much further? We really don’t know.
But if the concept is held to be true, that a Universe which is ‘only’ 13 billion years old, may in fact presently be bigger – than to have a size of 13 billion light-years – then this stumbles over very reliable Laws in Physics, which tell us that nothing can travel faster than the speed of light. And so an answer which has been put out there is, that ‘space itself has expanded’. This is a statement that would have profound implications if it should happen to be true, because it would imply that contrarily to common wisdom, space does not just consist of nothing.
But, by how much can (intergalactic) space have expanded? A hint might lie, in the factor by which the light has been red-shifted, and thus also reduced in frequency: slightly more than a factor of 9. If space really had the ability to expand, and did so as it seems, then it would seem natural to me to think that light traveling through space has also expanded (meaning its wavelength).
And so, if the light traveled 13 billion years to reach us, but has arrived at 1/9 its original frequency, it may be that the distance of the source of that light, has also increased by a factor of approximately 9. And so the present distance, of whatever became of that object, that we cannot observe, may be as far as 26 billion light-years.
Unless, 13 billion years ago, galaxies were traveling away from each other at 90% the speed of light.
(As Of 08/22/2018, 10h00 : )
What would not make sense, would be to suggest that the same object was originally 1.4 billion light-years away, but that it took light 13 billion years anyway, to reach us. And the reason for that would be the connected assumption, that originally, light would have started to close a mere 1.4 billion light-year distance. It was only as the light had already traveled, that the distances between such an object and our current position would have increased, for which reason the time it would have taken, was related more-closely, to the Integral of (x). The Integral of (x) , is 1/2 (x2) . ( –> :1 )
(Updated 08/23/2018, 22h50 : )
Another way to say the same thing would be, that if two objects were moving away from each other at relativistic speeds, and presently 13 billion light-years apart, then the light which Object A would be seeing as coming from Object B, would be light from less than 13 billion years ago, and that Object B would have moved since then. But then, just to suggest that the light which Object A is seeing would be 6.5 billion years old, would be a mere approximation, similar to the approximation which I made above, using the notion of an integral. ( :2 )
(As Of 08/22/2018, 10h00 : )
This line of reasoning also affects how we may explain the so-called “Two-Degree Kelvin Noise“, that radio-astronomers can measure as coming uniformly from space, but from apparently-empty regions of space. The official explanation for that is, that it’s ‘Thermal noise from The Big Bang itself, which has cooled down, due to the expansion of the Universe.’