What Actually Are Space And Time?

The Last Civilization

In the distant future, the last of a great civilization hides in the darkness as the universe is dying. They built a new home around a black hole to wait out eternity.

Building a New Home

• Engineers worked entire star systems and dismantled planets and asteroids to construct an immense interstellar empire.

• All of this is long gone now, and they are hiding in the darkness waiting for the end.

• They built a shell around a lost and lonely black hole using demolished worlds as raw material to completely enclose the darkness.

• Within this thin shell, barely withstanding the gravitational grip of their savior, they eked out their meagre lives.

Time Trickles More Slowly

• The black hole at their heart gave them greatest gift of all - time.

• Time trickled more slowly within the immense gravity of the black hole than outside it.

• Whilst many years passed outside, mere moments flashed by within the immense sphere.

• And so, they watched the future play out in front of them but knew that they had only delayed, not averted, their ultimate demise.

Einstein's Theories on Space and Time

Einstein's theories on space and time only begin to answer questions about what space is made of, whether time exists or not, and if hunting for their ultimate nature will lead to sudden clarity or make them more elusive.

Unanswered Questions About Space and Time

• Einstein's theories on space and time only begin to answer questions about what space is made of.

• Does time exist?

• Hunting for their ultimate nature will lead to sudden clarity or make them more elusive?

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The Lonely World Lingers On

The lonely world lingers on as its beating heart warps the very fabric of the universe around it. The civilization had done everything they could to keep going but could only bend reality; they could not break it.

Bending Reality

• The civilization had done everything they could to keep going but could only bend reality.

• They tried their best to put off the inevitable but knew that darkness would inevitably envelop them forever and ever.

• Their beating heart warped the very fabric of the universe around it.

The Birth of Modern Science

In this section, we learn about the earliest philosophers and their ideas on space. We also see how modern science began to take shape in the seventeenth century with the codification of physical laws and the use of mathematics.

Galileo's Sailor

• Galileo muses on a sailor locked below deck in a windowless cabin.

• The sailor experiences calm when tied up in port, but experiences turbulence when at sea.

• Galileo realizes that without a window to reveal the truth, there are no experiments the sailor could do to reveal whether the ship was moving or not.

• He concludes that any uniform motion is simply relative to any other uniform motion, leading to the first theory of relativity.

Isaac Newton and Gottfried Leibniz

• Isaac Newton was born in England in 1642 and is known as one of the greatest thinkers of his age.

• Gottfried Leibniz was born in 1646 in present-day Germany and was a leading thinker of his day.

• Their feud began over the development of calculus, with Newton claiming that Leibniz had stolen his ideas.

Conclusion

• Modern science began to take shape in the seventeenth century with the codification of physical laws and the use of mathematics.

• The birth of modern science can be traced back to early philosophers like Plato and Aristotle who had ideas about space.

Newton vs Leibniz on Space and Time

This section discusses the debate between Newton and Leibniz on the nature of space and time.

Absolute Space vs Relative Locations

• Newton argued that acceleration was relative to an absolute space, which is separate from objects themselves.

• Leibniz claimed that space in an empty universe devoid of matter made no sense. He believed that space only had meaning in the relative locations of objects.

• Newton's ideas about absolute space and time were accepted for nearly two centuries, but Galileo rejected absolute rest as a fixed point.

The Nature of Time

• For Newton and Galileo, everyone's clock across the universe ticked with absolute synchronicity. However, this may not be true.

• Time has a direction - a distinct past and coming future. Scientists can be pragmatic about it, but to understand it fully we must think about horses and steam engines.

• The question of how much work can you get out of a heap of coal led to the birth of thermodynamics.

What is Time?

This section explores different philosophical views on time.

Ancient Views on Time

• Aristotle saw time as simply the steps between before and after, while Hindu philosophers viewed it as cyclical from creation to destruction over four billion years.

The Nature of Time

• Like space, time seems obvious but is a different beast. We cannot freely travel through time, and it has a direction.

• The question of the ultimate efficiency of engines led to the birth of thermodynamics.

The Illusion of Perfect Efficiency

In this section, the concept of entropy is introduced as a measure to account for the increase in decay and disorder. It is explained that energy is always lost as heat flows from one place to another, and that even concentrated energy released from burning coal must be degraded as it flows through an engine.

Entropy and Probability

• Entropy is introduced as a measure to account for the increase in decay and disorder.

• Disorder is statistically far more likely than order due to probability.

• Physicists have revealed an inexorable growth in entropy as the universe marches on - a future universe destined to be more disordered and decayed than today’s.

Kelvin's Proposal

• Lord Kelvin proposed that although mechanical energy is indestructible, there is a universal tendency towards its dissipation which produces exhaustion of potential energy through the material universe.

• This led to questions about whether we are heading towards inevitable heat death with stars going out one by one in a steady march from potential energy to waste leaving the trillion-year-old universe dark and spent.

Maxwell's Demon

In this section, James Clerk Maxwell's views on thermodynamics are discussed. His thought experiment involving a demon who can sense each atom in gas leads to arguments over whether or not it breaks the laws of thermodynamics.

The Demon Experiment

• James Clerk Maxwell wondered what would happen if he introduced a tiny demon who could sense each atom in gas.

• The demon could turn around atoms, directing slow atoms to one side and fast ones to the other, effectively separating the warm gas into two unequal halves, one hot and one cold.

• Arguments over the meaning of Maxwell’s demon have raged for over 150 years. Some have stated that the demon must be expending energy to sort the gas atoms, while others propose that it is not energy but information that is important.

Entropy and Information

• The link between energy, entropy, and information has become stronger over time.

• Processing information generates a lot of waste heat. However, it is not simply the processing of information that leads to waste heat but also forgetting information.

• The Landauer limit provides us with the ultimate limit for forgetting - it is the inevitable release of energy from erasing a single bit.

The Arrow of Time

This section discusses the concept of entropy and how it relates to the arrow of time. It also explores whether the existence of the future is tied to our inability to remember.

Entropy and Forgetting Information

• Entropy increases due to the irreversibility of calculations.

• Forgetting information is essential for defining an arrow of time.

Meaning of Yesterday and Tomorrow

• The existence of yesterday and tomorrow may be tied to our inability to remember.

• Forgetting information is an essential ingredient in defining an arrow of time.

Future without Useful Energy

• In a distant future where all useful energy is used up, would time have any meaning? Fundamental physics does not yet have a definitive answer, but it is an intriguing possibility.

New Order Coming

This section discusses how the foundations of time and space can only get us so far, leading to a revolution that will lead directly to the last days of our lonely black hole world.

Turning Point

• We have reached a turning point where we need to explore new time and new space.

Foundations Only Get Us So Far

• The foundations of time and space are useful but can only get us so far.

Revolution Coming

• A new order is coming that will lead directly to the last days of our lonely black hole world.

Curious Minds Wondering About Universe

This section discusses how within their black hole shell, many civilizations resigned themselves to their fate and dozed their way to the end. However, a few curious minds still wondered about the universe.

Curious Minds

• A few curious minds with their dwindling energy still wondered about the universe.

Great Books

• Great books that had existed for almost eternity told them how space could bend and ripple.

• Central to these books was the story of light.

The Speed of Light

This section discusses how scientists knew that light's speed was immense and had used it to help measure their empire.

Light's Speed

• Scientists knew that light's speed was immense and had used it to help measure their empire.

• They knew that light was a limit they could never break, no matter how hard they tried.

• The speed of light had been the first step in the long journey to understand how the universe really worked.

Measuring Light's Speed

This section discusses how Danish astronomer Ole Romer found out that light must move at more than 211,000 km every second.

Observing Jupiter's Moons

• Romer observed the moons of Jupiter as they circled the giant planet.

• He timed just when they entered the gas giant´s planetary shadow, assuming that their orbits ticked like clockwork so he would be able to predict just when eclipses would begin and end.

Predictions Got Worse

• As he observed moon Io throughout the year, his predictions got steadily worse then better again.

• It became clear that the accuracy of his predictions depended upon our distance to Jupiter, and he would need to include the extra time taken by light having to travel further.

Light's Speed

• Christian Huygens calculated that light must move at more than 211,000 km every second, not far off our modern estimate of about 300,000 km per second.

• Romer’s observations confirmed that light was fast and finite.

James Clerk Maxwell's Demon

This section discusses how James Clerk Maxwell intertwined electricity and magnetism into a single idea - electromagnetism.

Light is Electromagnetic Waves

• Light was nothing more than a self-propagating combination of electricity and magnetism.

• Written into his equations was light’s blistering speed.

Problem with Light's Speed

• Just what was this speed relative to? Maxwell’s equations gave no answers, so physicists began to search for a solution.

Conclusion

This section concludes the video by discussing how Einstein wondered why electricity and magnetism would not obey Galileo’s relativity.

Einstein's Wondering

• Einstein wondered why electricity and magnetism would not obey Galileo’s relativity.

• Why should experiments specifically using electromagnetic waves give different results depending on whether they were moving or stationary?

The Revolution of Space and Time

In this section, the speaker discusses how Einstein's theory of relativity revolutionized our understanding of space and time.

Newtonian Mechanics vs Special Relativity

• Measuring the speed of light in a vacuum was constant, no matter the source.

• According to Einstein, everyone would measure the same speed of light regardless of their own motion.

• With special relativity, it was the speed of light that was absolute - not space and time.

Minkowski Space

• Herman Minkowski came up with an idea to explore the geometry of new equations in reaction to special relativity.

• Minkowski pointed out that it was simpler to mix space and time together into spacetime.

• Combined spacetime is known as "Minkowski Space."

General Theory of Relativity

• Newton's gravitational equations needed the distance between masses which special relativity told us no one could agree on what these distances were.

• Einstein spent a decade thinking about gravity and concluded that gravity as a force simply did not exist; instead, its effects were encoded within the curvature of space and time.

• Within his general theory, Einstein concluded that both space and time were relative and flexible.

Black Holes

• Karl Schwarzschild solved field equations for a spherical mass showing black holes bend both space and time with intense gravitational pulls where even light cannot escape.

• In the vicinity of a black hole, where gravitational fields are immense, time becomes more and more curved as you get closer to the center.

The Malleable Nature of Space and Time

This section discusses how Einstein's theory of general relativity was proven in 1919 through observations of the deflection of starlight. Scientists then turned their attention to measuring the effects of general relativity, leading to experiments such as Joseph Hafele and Richard Keating's in 1971.

Measuring General Relativity

• In 1971, Joseph Hafele and Richard Keating conducted an experiment using accurate caesium clocks and a set of jet plane journeys that completely encircled the Earth.

• The clocks were placed in the same location and synchronized before some were taken on planes heading east or west, moving with or against the Earth's rotation.

• Because they were flying, they were in a different gravitational field than the clocks left behind on the ground.

• After circling the world twice, all clocks were brought together. If Newton's absolute time governed the universe, they should have remained in sync. However, if Einstein was correct about relative motions and spacetime curvature desyncing them, they would differ by a few hundred nanoseconds.

Gravitational Waves

• In developing relativity, Einstein found that stretchy spacetime can wobble and ring like electricity and magnetism can ripple.

• Russell Hulse discovered pulsar PSR B1913+16 while peering at the universe with Edwin Hubble using Arecibo Telescope in 1974.

• With regular beeps from PSR B1913+16 pulsar orbiting another dead star heart neutron star, Taylor & Hulse found out that orbits were shrinking due to energy leaking out into space.

• Taylor & Hulse calculated how orbiting stars form ripples in spacetime, carrying away precisely enough energy to explain the orbital demise.

• In 1993, Taylor and Hulse received the Nobel prize for their discovery of gravitational waves.

• The Laser Interferometer Gravitational Wave Observatory (LIGO) was created to detect gravitational waves with unimagined sensitivity. It has opened a new window on the universe by uncovering merging black holes and collisions between neutron stars.

The Expansion of Space

This section discusses Alexander Friedman's realization in 1922 that the expansion of the universe is the expansion of space, which was later proved by Edwin Hubble.

The Big Bang

• Alexander Friedman realized that the expansion of the universe is actually an expansion of space in 1922.

• Edwin Hubble later proved this theory.

• The universe began expanding from an infinite point known as the Big Bang 13.8 billion years ago.

• Every galaxy is moving further away from us at an average rate of 70 km/s/Mpc except our local group.

• For every 3.26 million light-years distance from us a galaxy is, it moves away from us at an extra 70 km/s/mpc.

The Expanding Universe and the Curvature of Spacetime

In this section, we learn about the complexity of understanding the curvature of spacetime in an expanding universe. We also explore how the decrease in density across the universe is not uniform and how it affects energy conservation.

Understanding Spacetime Curvature in an Expanding Universe

• The expanding universe makes curving and bending spacetime even more complex to understand.

• As equations show that space is infinite, what is happening is that the universe is actually becoming less dense.

• This decrease in density is not completely uniform across the universe.

• Individual galaxies hold themselves together due to their mutual gravity, which is a manifestation of the curvature of space.

• What happens at the boundary between expanding and non-expanding space?

• Energy conservation becomes a problem for physicists as expanding space breaks one of the key properties of the universe - conservation of energy.

Spacetime: Physical or Not?

In this section, we explore whether spacetime has physical properties or not. We also discuss how time was affected by Einstein's theory of relativity.

Is Spacetime Physical?

• Nobel prize winner Steven Weinberg claims that in Einstein’s relativity, spacetime is truly nothing.

• The mathematics look like bending and curving but in reality, relativity tells us space is nothing and has no properties.

How Was Time Affected by Relativity?

• Time meant many things to future civilizations who understood that clocks ticked differently depending on where you are and what you are doing.

• Engineers used the malleable nature of spacetime to shape their civilization, creating great portals of distorted time and space for travel across the empire.

• With the coming of Einstein’s general relativity, physicists were presented with a new headache as there is no such thing as a unique present or a true instant of now.

• Within the equations of relativity, all pasts, presents, and futures are already written.