The concept of deep time
Deep Time
Some would argue that the time that had passed since the Big Bang compared to the time that is yet to come is insignificant; such claim is questionable, given the following. Firstly, to claim that 13.7 billion years is insignificant in a comparison implies a much larger quantity, one that might tend to infinity. Secondly, the universe has been expanding ever since, such behaviour must have a limit, unless the universe, given an infinite amount of time, perpetually expands. Perhaps It is an exaggeration to use the infinity concept as it only raises more questions, therefore a numerical assumption will be made regarding deep time. The only question that emerges would be, what would happen to the universe at the end of time?
It could collapse upon itself analogous to a balloon inflated beyond its limit. However, It is probable that the universe will conclude in some fashion, because if it doesn't, and deep time is infinite as hypothesised earlier, then the universe is approaching infinity while violating the concept as it had a beginning. Death is an inherent component of the cycle of life; the universe might not be living, but so are stars. Therefore, in my humble opinion, there shall be a time, not necessarily in the distant future, where the universe will die out, and nothing will be left, just akin to pre Big Bang era.
Contemplating the fate of the universe is based on incomplete circumstantial evidence. There are many guesses, but no one knows.
Well based on the scientific method, one can hypothesise that the universe will end in some fashion, given the observable nature of the content of the universe i.e. everything dies eventually such as stars and with them planets, trees, animals etc.
However, there is one fascinating book that describes the end vividly, it is quite old, but the content is surprisingly millennia ahead of its time. The book is the Quran, specifically chapters The Catastrophe, The Earthquake, The Bursting Open, The Splitting, The Enfolding, The Inevitable and The Smoke. I recommend you read the English translation of these chapters.