Create a list of the twenty most important questions that remained unanswered by humankind.  

Arrange these questions into a timeline and make some educated predictions as to when they will be answered, and by whom.
Here's a list of twenty important questions that remained unanswered by humankind, arranged into a timeline:

1. What is the origin of the universe, and how did it begin?
2. What is dark matter, and how does it affect the universe?
3. How did life originate on Earth?
4. What is the nature of consciousness, and how does it arise?
5. What is the true nature of reality?
6. Is there extraterrestrial life in the universe, and if so, where and in what form?
7. What is the cure for cancer and other diseases that afflict humankind?
8. What is the ultimate fate of the universe, and will it end in a big crunch, big rip, or heat death?
9. How can we develop a sustainable society that meets the needs of the present without compromising the ability of future generations to meet their own needs?
10. How can we reverse or mitigate the effects of climate change?
11. How can we achieve world peace and eliminate war and conflict?
12. How can we eradicate poverty, hunger, and inequality?
13. How can we ensure the ethical use of advanced technologies, such as AI and genetic engineering?
14. What is the nature of dark energy, and how does it affect the universe?
15. What is the relationship between the mind and the brain?
16. How can we achieve true artificial general intelligence, and what are the risks and benefits of such technology?
17. What is the mechanism behind gravity, and how does it fit into a unified theory of physics?
18. How can we preserve biodiversity and prevent the extinction of species?
19. How can we develop sustainable and scalable energy sources, such as fusion power?
20. How can we extend human lifespan and improve the quality of life in old age?

As for when and by whom these questions will be answered, it is impossible to predict with certainty. However, many of these questions are actively being researched by scientists, engineers, and other experts in various fields, and progress is being made every day. It is likely that some of these questions will be answered within the next few decades, while others may remain mysteries for centuries or even millennia.
Ok. Tell me which ones you think will most likely be solved within the next few decades, and why.
Based on current research and advancements in technology, some of the questions that are most likely to be solved within the next few decades are:

1. What is the nature of dark matter, and how does it affect the universe?
Recent experiments, such as the Large Hadron Collider, have provided new data and insights into the properties of dark matter. With ongoing research and improvements in technology, it is likely that we will have a better understanding of dark matter in the coming decades.
2. How can we reverse or mitigate the effects of climate change?
There is currently a global effort to address climate change, with governments and businesses investing in renewable energy and implementing policies to reduce carbon emissions. Continued research and development of new technologies, such as carbon capture and storage, could also contribute to mitigating the effects of climate change.
3. What is the mechanism behind gravity, and how does it fit into a unified theory of physics?
Theoretical physicists are actively working on developing a unified theory of physics that would encompass gravity and other fundamental forces. Recent developments in string theory and quantum gravity have provided new insights into the nature of gravity, and it is possible that we may have a better understanding of gravity within the next few decades.
4. How can we achieve true artificial general intelligence, and what are the risks and benefits of such technology?
Advancements in artificial intelligence are happening rapidly, and there are ongoing efforts to develop AGI that can perform a wide range of tasks. However, the ethical and societal implications of AGI are still being debated, and it is crucial that we consider the potential risks and benefits of such technology as we continue to develop it.
5. What is the nature of consciousness, and how does it arise?
Recent research in neuroscience and cognitive science has provided new insights into the nature of consciousness and how it may arise from the brain. Continued research in these fields could lead to a better understanding of consciousness within the next few decades.

Overall, it is important to note that scientific progress is often unpredictable and can sometimes occur in unexpected ways. Therefore, while these questions may seem likely to be answered within the next few decades, it is always possible that breakthroughs in other fields could lead to surprising discoveries and advancements in these areas as well.