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It is an exciting start to the second Season of the Information Finding Championship by @ifc and @apolymask! This season, we have abandoned our lovely Castle home and taken to space in a comfy space cruiser... Hopefully, cabin fever won't break out! Anyway, this is my entry for the first round of Season two, with the topic of 'Universe'.

Introduction

Well, the topic of "Universe" is a pretty broad topic by definition... there are so many things that are contained in that little word that you could write about! Definitely, I wanted to write about something that was interesting to me... space, physics... that sort of thing. Eventually, I did hit upon a topic that I had wanted to be showing off to my daughter anyway.

This past year, we've had a couple of well publicised eclipses, the total eclipse of the Sun and more recently, the Lunar eclipse. Now, based on the covereage, you would think that these were pretty rare circumstances... however, they do happen relatively often, just most often in areas that are either hard to get to or not in the United States. This year, the United States happened to be lucky enough collect the prime examples of both eclipses.

So, this got me to thinking about galactic blackouts... and I thought I would write about the coming blackout of the entire Universe! Take that, Americans! You will have to share this one with the rest of us!!!

PS: I am going to keep this to simple physical concepts in plain-ish English.. so you will have to deal with my inprecise translation of the mathematics to words. If it is a topic that is interesting to you, then there are books that also deal with matters of Mathematics and Theoretical Physics in a similar style (but the language is so imperfect to describe with....).

TL:DR? The Universe is disappearing due to a giant rift from which the Hordes of Chaos will spew out... don't believe me, read the actual post!

The setup

To begin with, I need to make clear two fundamental properties of our Universe as we currently understand it. These ideas are incredibly interesting topics in their own right and are full of ideas that are completely mind-blowing in that they highlight how limited (however vast and varied and interesting) our experience of reality is in comparison to what the Universe can offer! However, they are only required as an initial primer (assumed knowledge) for the topic of the post.. but I will provide starting links for those who are interested in further reading!

1. Speed of Light

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One of the two basic assumptions (otherwise known in logic as "postulates") of Einstein's Special Relativity is that the speed of light (c) in a vacuum is constant for all observers, regardless of motion. At the time, it was a big claim to have made (even now, can be a counter-intuitive), as our everyday experience of objects is you have a simple vector addition of velocities. However, to this day, Special Relativity has made predictions based upon this assumption that have been verified by experiment (even when they defy our everyday intuition of what should be!). Ideas such as Simultaneity, Equivalence of Mass and Energy, Time Dilation and Length Contraction. The best known of these outcomes is the Mass-Energy equivalence (E=mc^2) which is the foundational idea behind our Nuclear Theories, whilst the other outcomes have redefined our understanding of time and space.

However, for this post, the outcome that we require is actually the original postulate; that light (Electromagnetic Waves) travels in a vacuum at exactly c=299792458m/s regardless observer or any other properties of the the light (such as wavelength).

2. Universe Expansion and Redshift

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For some reason which is not pinned down yet, the Universe is expanding at an accelerating pace. Everything is expanding, however it is not that space is expanding into anything, it is such that the scaling of space itself is expanding. This has the effect that things closer to us move away slower than things that are far away (the far away objects move away faster). A touch confusing, however, I recently heard a good analogy which helps to explain what is going on.

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Imagine you were in a theatre, and you were seated next to your friend. For some reason the theatre seating expands... as in one extra seat was placed in between each existing seat (thus displacing them all away from each other as well). You would (from your reference frame in which you assume that you are stationary) perceive your friend moving away from you. If this happened at regular intervals, then you would eventually be quite far apart....

Now imagine a row of three of you, with you seated to the end of your two friends. Now, insert the extra seats in between each of the existing seats. Your immediate neighbour has moved away by one seat, whilst your friend on the other end has moved away by two seats. Thus ends the analogy!

A side effect and observable phenomenon of this expansion is the shifting of light (Electromagnetic Waves) emitted by objects (that are moving away from us, due to the universe expanding) into the red direction of the spectrum when they are detected by us. The further away the object, the greater the redshift (remember the chairs!).

So, further objects move away faster than nearby objects due to the expansion of the Universe, and in doing so, the light that they emit is red-shifted when observed by us!... the second of our little pieces of assumed knowledge for the real meat of the post!

For further reading, you can begin here for the Expansion of the Universe and here for the Redshift.

The Darken-ing

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How is that for a clumsy attempt to coin a term, I'm pretty sure that that won't catch on.....

Now, if we combine these two concepts of a constant speed of light and the fact that the Universe is expanding then we come up with a logical outcome that there are objects that are emitting light (note, that this is the only way that we have of interacting or observing objects in the Universe) that we will never see!

Behold my lovely artistic skills (my child has better skills).

In the diagram above, I have tried to visualise this concept for you. Within a certain sphere (represented in the 2D sense of a circle), we have light travelling to us whilst the intervening space is expanding at a rate LESS than the speed of light. This means, it WILL reach our eyes... however, it will be red-shifted according to the distance between us and the emitting object.

However, the further away from our position that we go... the faster the rate of the Universe expansion, and thus, there is a point (sphere) where the expansion of the Universe is EQUAL to the speed of light. Thus, the light WILL never reach us... in fact, just before this critical point, the light is shifted so far to the red direction that is barely detectable.

Beyond this critical point, we see nothing... and will NEVER see anything!

Now... remember that the Universe is expanding at an accelerating rate! This means that the critical sphere (where the expansion rate EQUALS the speed of light) is shrinking inwards. So, this means that the sphere of the observable Universe is also shrinking, as nothing outside this sphere is visible or detectable.

In fact, everything within the sphere is being shifted further and further in the red direction of the spectrum as it gets physically closer to the critical shrinking sphere until...NOTHING!

Wrapping up

So, if you made it this far... the observable Universe is disappearing from our view, in a perfectly normal and physically consistent sort of way, so there was no need to call upon the Rifts of Chaos this time. Needless to say, it is a sobering thought, despite the fact that it lies a very very very long way in our future...

PS: I have had to simplify a lot of concepts here for a general audience, if you have more specific questions, I can try and answer them as best as possible in the comments... or point you to a resource or person that would be better able to. I'm afraid that words, whilst poetic, are not exactly precise... and my Mathematics is a touch rusty after decades of minimal practice...