Did The Past Really Happen?

Source: Did The Past Really Happen?, Vsauce, 11:56, uploaded 2015-02-06, category hint Computer Science / AI, playlist index 1481.

Michael Stevens begins with Terry, the dog who played Toto in The Wizard of Oz. Terry died in 1945 and her owner, Carl Spitz, buried her on his Los Angeles ranch. The Ventura Highway later cut through the grave, disturbing the remains. In 2011, Hollywood Forever Cemetery erected a memorial for Terry, although the dog is not buried there. The memorial is a cenotaph, an empty tomb.

Stevens connects Terry’s cenotaph to the cenotaph of Philopappos on the Hill of the Muses in Athens. A trip to Greece had taken him past the Acropolis, a Lion Gate nearly a thousand years older than the Acropolis, what he calls the earliest known analogue computer, and the cats of Delphi. Ancient sites make the present feel temporary. They also raise a more personal question: how will future archaeologists reconstruct the ruins of our society, and will anything about one person survive their account?

Last Thursdayism and the burden of proof

The question then widens. A person can ask whether the past happened at all, including the photographs, memories, and traces that seem to prove it. Last Thursdayism gives that doubt a name. It proposes that the universe appeared last Thursday with every person, memory, and object already in place. The proposal has no rituals or real community, and no observation can disprove it because every objection can belong to the universe created last Thursday.

That makes Last Thursdayism unfalsifiable. Stevens places it in philosophy because a scientific explanation must allow some possible observation to show it false. Philosophical razors can still compare explanations, even when an experiment cannot settle the question.

Occam’s Razor says to choose the explanation that requires fewer assumptions. A Bronze Age tomb that Stevens visits today needs a long history, yet it asks less of the evidence than a tomb, his memory of the visit, and the footage of him inside it appearing together last Thursday. The razor does not prove that the past happened. It gives ordinary history a better fit with the available evidence.

Stevens then introduces Newton’s Flaming Laser Sword: if an issue cannot be settled by experiment, it is not worthy of debate. The past cannot be placed in a control group or tested with a trial. It simply was what it was. We will also become the past, leaving future archaeologists to make guesses even when we spend our own lives recording what happened.

Future archaeology and selective memory

Future humans will probably know more than people today about medicine, exoplanets, and physics. They cannot know more about the present than the people who live in it. Their knowledge of us will depend on what survives and what seems worth keeping. Stevens asks whether a person’s descendants will know their name, and whether aliens arriving millions of years after human extinction will understand that Animorphs was fiction rather than a historical account of humanity.

Vandals, fire, natural disasters, conquerors, and thieves can destroy evidence. A quieter force does more lasting work: apathy. Ira Glass once asked listeners to name ten people from the fifteenth century. The records contain many names, yet most of them carry no meaning for a present-day listener. In five hundred years, Stevens expects a radio host to make the same joke about people alive now.

He gives the future one reliable record. Energy is conserved. Turning off a light saves the resources that would produce its electricity, yet the total energy in the universe remains the same. Energy also spreads when nothing holds it back. That spreading is the Second Law of Thermodynamics, and it gives every action a physical trace even when history loses the name of the person who acted.

Energy, entropy, and what remains

The Second Law does not say that every local arrangement must become visibly messy. A crystal can form and life can grow whilst the wider system still allows energy to spread. The local concentration works because the process is connected to a larger world and cannot use energy with perfect efficiency. Balloons deflate, hot objects cool, objects fall, and perfume moves across a room because energy eventually disperses.

Entropy measures how widely energy has spread. Stevens separates that measure from ordinary messiness with a deck of cards themed around Greek philosophers. The deck begins ordered by value and suit. Shuffling changes its visible arrangement, yet it does not change the energy inside the cards. The wider world gains entropy because Stevens’s body uses concentrated chemical energy to move the cards. That energy becomes movement, heat from friction, and sound from the rustling paper.

The shuffle supplies Stevens’s account of a lasting legacy. History can forget a person, misread their work, or send their effects in a direction they never intended. The net increase in entropy remains in the universe. No later process can undo it. The claim gives physical permanence to a life that may leave no readable story, although “legacy” here describes an irreversible change in a physical system rather than a human meaning that survives.

Heat death and the cost of motion

Many scientists, Stevens says, expect the universe to move towards thermodynamic equilibrium. Heat would spread evenly until no region had the difference needed for anything to happen. The video calls this the heat death of the universe and gives an estimate of roughly eight googol years. Change requires energy to spread, so a universe with energy spread as evenly as possible would have no remaining movement to support change.

That conclusion gives the video its small joke about laziness. A person who lies around and does very little contributes less to the dispersal of energy than a person who stays active. Sloth may count as a vice in human life, Stevens says, while resting postpones the heat death by an amount so small that it is almost indistinguishable from zero. The amount remains theoretically real. His closing thanks go to the viewer for taking it easy.

Limits

This note follows Stevens’s argument and examples rather than independently checking every scientific or historical claim. The video presents the account of Terry, the future-archaeology examples, the Ira Glass question, and the estimate of eight googol years without a bibliography in the spoken material. Its explanation of entropy is a teaching model, and its language of a person’s “legacy” turns an irreversible physical effect into a human question about remembrance. The thermodynamic claim does not preserve a person’s identity or intentions. It says that action changes the state of the wider universe.

Further reading / references

• David Macaulay, Motel of Mysteries
• John Baez, Occam’s Razor
• Newton’s Flaming Laser Sword, the philosophical razor Stevens names.
• Ira Glass, Memo to the People of the Future, This American Life, episode 167.
• The 15th century, the Wikipedia page Stevens mentions in the discussion of historical memory.
• Conservation of energy, Encyclopaedia Britannica.
• The Second Law of Thermodynamics, HyperPhysics.
• Heat Death of the Universe, PhysLink.