TLDR;
The video explores the concept of the universe's size and whether it is finite or infinite. It discusses the observable universe, the possibility of a finite but boundless universe (like a hypersphere or hyperdonut), and the implications of an infinite universe, including the potential for identical copies of ourselves. The video concludes by acknowledging that while these concepts are fascinating, they are currently untestable and reside in the realm of science philosophy.
- The observable universe is limited by the speed of light and the age of the universe.
- A finite universe could be shaped like a hypersphere or hyperdonut, which are boundless but finite.
- An infinite universe raises paradoxes, such as how it can expand and the possibility of identical copies of ourselves existing far away.
- These concepts are currently untestable and reside in the realm of science philosophy.
Introduction [0:04]
The video starts by posing fundamental questions about the universe: Is it infinite? Does it have an edge? And what would one see at the edge? It introduces the concept that the universe had a beginning 14 billion years ago and has been expanding ever since, which leads to the question of whether it has an edge.
The Observable Universe [0:24]
Because information can't travel faster than light, we can only observe the portion of the universe whose light has reached us in the last 14 billion years, forming a sphere centered on us known as the observable universe. Due to the universe's expansion, the most distant objects we can see are currently 45 billion light-years away. The observable universe contains approximately 200 billion galaxies, each with hundreds of billions of stars. For us, there is an edge in time, representing the limit of what we can observe in the past, but the real universe is likely much larger than what we can see.
Finite Universe [1:21]
The video presents two possibilities: a large but finite universe or a truly infinite one. A finite universe would contain a finite amount of "ice cream," but it raises the question of what exists beyond its edge. To address this, the video introduces the concept of a universe without borders, such as a hypersphere, where 3D space is curved on itself. In this model, traveling in a straight line would eventually lead back to the starting point, similar to an ant walking around an orange. Gravity bends spacetime, potentially causing the universe to curve back on itself, forming a hypersphere.
Hyperdonut Universe [4:11]
Another possibility is that the universe could be shaped like a hyperdonut, which is also impossible to visualize. In this scenario, traveling in a straight line would also lead back to the starting point, but with complications. The amount of stuff in every direction would not be the same, and light from faraway galaxies would create a cosmic hall-of-mirrors effect. It could allow us to see a star being born on one side of the sky and dying on the opposite side due to the different travel times of light. A hyperdonut universe could potentially be just a few times bigger than the observable universe.
Infinite Universe [5:27]
The video then explores the possibility of a truly infinite universe, which is the model used by most scientists. An infinite universe goes on forever without any borders. Cosmic expansion means that the distance between galaxies is growing with time, even in an infinite space. As one travels in a straight line, they would encounter new galaxies, stars, planets, and potentially even an exact copy of themselves. This is because everything is made of a finite amount of different particles, which can only be combined in a finite number of ways. In an infinite space, repetition is likely to occur by pure chance.
Implications and Conclusion [8:42]
Despite the possibility of identical copies, the likelihood of finding a second identical Earth is incredibly small, requiring travel to a distance that is practically forever away. The video acknowledges that these scenarios are currently untestable and reside in the realm of science philosophy. For us, the universe is finite and has an edge in time, represented by the observable universe. The video concludes by stating that even if this finite universe feels small, it is more than big enough to fulfill all our dreams.
Brilliant.org Sponsorship [9:34]
The video includes a sponsorship message for Brilliant.org, highlighting its interactive lessons in science, math, and technology. It mentions new data courses that use real data to teach analysis techniques and a series of lessons that further explore topics from Kurzgesagt's popular videos. Viewers are offered a free 30-day trial and a discount on an annual membership.