Albert Teen

YOU ARE LEARNING:

What goes on in black holes? and what is the dark matter and energy that makes up 96% of the Universe? Nobody knows!

There are many things in physics that are still a mystery. This lesson will briefly introduce you to some of them.

The Universe is expanding, and it is doing so faster and faster and faster.

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How do we know that the Universe is expanding?

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In 1998, astronomers found that galaxies are actually moving away from us faster and faster. So the expansion of the universe is accelerating. There must be some energy that makes that happen, but scientists don't know what it is. What do you think they call it?

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Scientists can't currently explain what it is that causes the acceleration of the Universe

They believe some form of energy must be the fuel for this acceleration, but it is an unknown form of energy. They have given it the name dark energy.

Scientists also cannot explain why there are some galaxies which are rotating faster than they should be, according to the physics that describes them.

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It's gravity that causes galaxies to rotate. In order to work out exactly how fast a galaxy is spinning, what variable do scientists need?

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So the rotation of an object depends on gravity, which is determined by its mass.

The more mass an object has the faster it spins due to gravity.

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The mystery is that galaxies are spinning faster than they should be able to when we look at the amount of mass they have. So scientists believe that...

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So scientists believe there is an unknown, invisible form of mass that means the galaxies are actually heavy enough to spin as fast as they are spinning. What do you think scientists call this unknown form of mass?

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So scientists believe there is an unknown, invisible form of mass in the universe, which they cannot measure.

They have named it dark matter. We can only detect it by the effect its gravity has on nearby objects. Astronomers have calculated that 27% of the universe must be made of this dark matter! That's a huge part!

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What's this?

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Black holes are the most massive objects in the Universe, so their gravitational field strength is...

A) the strongest in the Universe. B) the weakest in the Universe.

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A black hole is essentially...

A) a sun that shines black. B) a hole someone poked in the universe. C) a dead star.

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Black holes are created when the biggest supernovas implode and gravity pulls all the mass into an extremely dense point, the centre of which is called a singularity.

Scientists have no clue what goes on in a singularity. In fact, we may never know because anything that comes close enough to the edge of a black hole can never escape. It simply gets sucked in!

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So if it isn't actually a hole, what makes a black hole black?

A) Even light can't escape the black hole. B) They are so far away that no light has come through to us yet. C) They are always in shadow, so they are always eclipsed.

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Black holes appear black because we can't see any light reflected or emitted from them

They are essentially invisible to us. We can only see the edge around them where light is still just about able to escape. We call that the event horizon.

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It get's crazier! The gravitational pull of black holes is so strong that it warps time!

Einstein's theory of relativity explains how space and time are actually the same thing, and gravity affects both.

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This adds to the mystery about what happens in a singularity, where there might be an infinite amount of mass in a single point in space

If then there is an infinite amount of gravity, the laws of physics don't make sense anymore, so scientists really don't know whats happens in the centre of a black hole.

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You will probably have learnt mostly about Classical Physics

But there are two other very important parts of physics: Quantum Mechanics and Relativity.

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Quantum Mechanics and Relativity...

are only about 100 years old, but they are fundamental to how we understand the Universe and how we have developed technology.

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The 4 fundamental forces in physics are gravity, electromagnetism, the weak nuclear force, and the strong nuclear force

Relativity explains gravity, but Quantum Mechanics explain the other three.

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Ideally we want a theory which explains gravity in terms of ** quantum mechanics, so that one theory could explain all 4 fundamental forces in physics.

We would call that theory Quantum Gravity.

Summary

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We don't know why the Universe is expanding faster and faster

Scientists believe the fuel for this acceleration must come from an energy form they have named dark energy, but they don't really know what it is.

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Galaxies are spinning faster than they should

Scientists believe this is because there is a form of mass that we can't see and we can't measure. They call it dark matter.

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We have no idea what is going on in a black hole

Maybe we will never know, because everything that comes too near one will get sucked in. They are essentially invisible to us, because light can't even escape its gravitational pull!

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We don't have a single theory that can explain physical phenomena in all conditions

Sometimes Classical Mechanics works, sometimes Quantum Mechanics works. But the two theories don't always work together, so there must be something we don't know.

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In conclusion

There are still some fascinating, fundamental truths about the Universe that physics is yet to discover!