The Universe's Curvature, Age & Fate

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  • 0:01 What Is Fate?
  • 0:57 The Age and Curvature…
  • 3:24 Constant Dark Energy
  • 5:29 Dynamic Dark Energy
  • 7:47 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

What is the age of our universe? What shape does it take? What determines the fate of our universe and what is this fate? This lesson will tell you all of this and more!

What is Fate?

One of the greatest essayists, Ralph Waldo Emerson, once opined that 'fate is nothing but the deeds committed in a prior state of existence.' Emerson was likely talking about a sort of karma or future circumstance that happens upon a person as a result of his or her past actions. But this quote can be applied to the fate of our universe, for its fate is indeed a reflection of what it once did and what it once caused to occur. The universe's fate is nothing more than a reflection of its past and present properties.

The problem is, just like you do not know your fate and neither do I mine, we do not truly know the fate of our universe. However, this lesson will present for you some possibilities and which one is most likely to be the correct one based on modern evidence.

The Age and Curvature of the Universe

The universe is estimated to have an age of approximately 13.7 billion years, give or take a little bit. How much longer do we have until it's all over? We don't know for sure. What astronomers are more certain of is the curvature of the universe. More specifically, the lack of any real curvature. The structure of our universe is deemed to be flat instead of spherical or saddle-shaped. The way this was figured out was covered in multiple lessons on the models of our universe, inflation, and acceleration of the universe which I urge you to look over.

Nevertheless, at one point, the universe was extremely small - smaller than the nucleus of an atom. But it underwent inflation, a period of time where it expanded to a great size. This inflation helps, in part, explain why our universe is flat.

Let me explain why in an example. If you stand on the surface of an inflated basketball, you'll be able to clearly tell that the basketball is curved. That's obvious. Now, let's say that basketball all of a sudden inflated to the size of planet Earth, and it actually became Earth itself. Now you're standing on planet Earth's surface. Not knowing any better, like our ancestors, you'll look out and think that the Earth is flat. That's because the radius of the Earth is so huge, its curvature at any given observable point on its surface is too small to distinguish, so things appear flat.

Similarly, the universe may have been curved originally, but during the era of inflation, the observable universe became flat. This flat universe is consistent with one whose density equals critical density, as we believe our universe does. We believe it equals critical density namely because of dark energy, a force that accelerates the expansion of our universe. The form that dark energy actually takes will determine the fate of our universe. Therefore, the way the universe has evolved, its past deeds and current condition, will determine its fate, as Emerson so succinctly put it.

Constant Dark Energy

Dark energy itself may be constant or it might not be. Meaning, dark energy might be a property of space that exerts a constant pressure and causes space to expand. Another possibility is that dark energy is a force that could change the acceleration of our universe with time.

Let's explore what I mean. If the cosmological constant governs dark energy, then the force of acceleration is constant - it doesn't change with time. This means our universe will expand forever. The cosmological constant, by the way, is an anti-gravity property of space proposed by Einstein. As the universe expands forever, the galaxies will get farther apart. As they move farther apart, they will eventually use up all of the gas and dust that helps to form stars. The stars will die and each galaxy will simply burn out all alone somewhere out in space. The galaxies will fade away and the universe will darken.

If you watched the lesson on cosmic recycling, you might be thinking: why don't the stars just recycle the usable fuel forever and always remain alight? But recall that as a star lives, usable fuel is converted to other things. Therefore, as a dying star releases its contents into space for new stars to use as they are born, only so much of it can be used as fuel to set a new star alight. With every generation of stars, the usable fuel and raw ingredients for stellar formation will get smaller and smaller.

If you've ever reused something like a plastic sandwich bag over and over, you've surely noticed that it became more brittle with time and maybe even developed holes. You can only reuse the material so much before it's no longer usable. This also happens in the cycle of star formation and death.

Dynamic Dark Energy

At any rate, if the dark energy is not constant, however, then two other scenarios are possible.

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