Is the Physicist's Eulogy True?

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In 2005, the writer and performer Aaron Freeman recorded a short commentary for NPR's All Things Considered. It opens with a piece of advice: you want a physicist to speak at your funeral. What follows is a few hundred words of thermodynamics, offered as comfort. Your energy, he says, is still here. Not a bit of you is gone.

The piece has travelled a long way since then. It is read aloud at memorials, printed in funeral programmes and passed around whenever someone wants words of comfort that don't depend on religion. It is reprinted on site after site. What almost nobody does is check it. So we did, line by line.

The short answer: mostly yes. The physics at its heart is among the most thoroughly tested in all of science. Where it stretches, the truth turns out to be stranger, and in one place far bigger than Freeman claimed.

Claim 1: Energy Is Never Created or Destroyed

This is the backbone of the eulogy, and it is solid. The conservation of energy, known in thermodynamics as the first law, says that energy can change form (chemical energy into heat, heat into light, motion into sound) but the total never changes. It has been tested in every corner of physics since the 1840s, from chemistry benches to particle colliders.

Physicists trust it so deeply that when energy seemed to go missing in radioactive decay in the 1920s, they refused to give the law up. In 1930, Wolfgang Pauli proposed that an unseen particle must be carrying the missing energy away. Twenty-six years later, that particle, the neutrino, was detected. The law had been right all along.

There is a deeper reason it holds. In 1918, the mathematician Emmy Noether proved that conservation of energy follows from one simple fact: the laws of physics don't change over time. As long as tomorrow's physics is the same as today's, energy is conserved.

One honest footnote: on the scale of the whole expanding universe, energy becomes harder to define, because space itself is stretching. On the scale of a person, a planet or a solar system, the law holds without exception.

Verdict: true.

Claim 2: Your Energy Is Still Here

A human body runs on food, and nearly all of that food energy ends up as heat. An adult eating about 2,000 calories (kilocalories) a day releases energy at roughly 100 watts, about the same as an old incandescent light bulb. Over an 80-year life, allowing for smaller appetites in childhood, that comes to something like 200 billion joules: roughly 60 megawatt-hours, about what a typical American home uses in five or six years.

So where did it go? Into the air around you, the chair you sat on, the people you held. Warm air rises and mixes, and that heat spreads through the atmosphere. In the end, almost all of it leaves the planet. Earth stays at a roughly steady temperature because it sends energy back into space as infrared light, in balance with the sunlight it absorbs. The warmth of a life becomes part of that glow.

Freeman is right that it is still there. What isn't still there is the shape. The energy hasn't stayed together as a recognisable "you". It has spread out into the world, which is exactly where the eulogy ends up.

Verdict: true, with one clarification. Your energy isn't gone, but it isn't kept in one place either. It is dispersed through the air, the ground and, eventually, the sky.

Claim 3: "Hundreds of Trillions" of Photons

One of the eulogy's most moving images is of light: all the photons that bounced off a person's face over a lifetime, their paths changed by a smile. Freeman puts the number at "hundreds of trillions".

This is the one place where the eulogy is wrong, and it is wrong in the most generous possible direction. The real number is vastly larger.

Here is a rough estimate you can check. A well-lit room is about 500 lux, which is very roughly 1.5 to 2 watts of visible light per square metre. Each photon of visible light carries a tiny amount of energy, so that works out to a few billion billion photons per square metre every second. A face presents about 0.04 square metres to the light and reflects a sizeable fraction of it, very roughly a third to a half. Put together, a face in an ordinary room scatters on the order of 10¹⁷ photons every second, a hundred quadrillion.

At that rate, Freeman's "hundreds of trillions" goes by in a few thousandths of a second. Over a lifetime of waking hours, with days spent outdoors in sunlight that is a hundred times brighter, the total runs to something like 10²⁶ photons or more: a hundred million billion billion.

Verdict: true, but understated by a factor of hundreds of billions.

Claim 4: That Light Reached the People Who Loved You

The eulogy imagines those photons landing in the eyes of the people who loved you. This one is literally true, and it is more intimate than it sounds.

When a photon reaches the retina, it is absorbed by a molecule called retinal, held inside light-sensitive proteins such as rhodopsin. The energy of that single photon twists the molecule into a new shape, and that change sets off the chain of signals the brain experiences as sight. The biochemist George Wald shared the 1967 Nobel Prize in Physiology or Medicine for working out how this happens.

So every time someone looked at you, light that had just touched your face was absorbed in their eyes and changed, for an instant, the shape of molecules inside them. That isn't a metaphor. It is how seeing works.

Verdict: true.

Claim 5: "You're Just Less Orderly"

The eulogy closes by saying that not a bit of you is gone, that you're "just less orderly". It is the most precise sentence in the piece.

The second law of thermodynamics says that in any closed system, disorder (entropy) tends to increase. A living body is an astonishing island of order, kept that way by constant work. When that work stops, the energy and the atoms that made it up don't vanish. They spread out and mix with everything else. "Less orderly" is exactly the right physics.

The same is true of matter. A human body contains roughly 7 billion billion billion atoms (7 × 10²⁷). None of them are destroyed by death. Ordinary chemistry, including decomposition and cremation, rearranges atoms but cannot unmake them. Over time they return to the air, the soil and the water and become part of other living things, just as they were part of other things before they were part of you. Most of them were forged in stars long before Earth existed.

What physics cannot tell you is whether memory, personality or a self continue in some other way. That lies outside anything an equation can measure, and the eulogy doesn't need it. Its promise is narrower: that everything you were made of is still here. That promise holds.

Verdict: true, for energy and for matter.

The Verdict, Line by Line

• Energy is never created or destroyed: true. It is the first law of thermodynamics, tested since the 1840s.
• Your energy is still here: true, though spread out rather than kept together. Most of it eventually leaves Earth as infrared light.
• Hundreds of trillions of photons bounced off your face: true, but far too modest. The real lifetime figure is around 10²⁶.
• That light reached the people who loved you: true. It was absorbed in their eyes and changed molecules inside them.
• Not a bit of you is gone, you're just less orderly: true for energy and matter, and the most precise line in the piece.

Reading It at a Service

Freeman's commentary is one of the most popular non-religious readings for funerals and memorials, and it is easy to see why. If you plan to read it, credit Aaron Freeman and NPR, and take the wording from the original NPR transcript, because versions passed around online are often adapted or shortened.

It can sit beautifully beside something personal: a few of the person's own numbers, like how many sunrises they saw or how far the Earth carried them through space. That is why we built Swayanta's memorial mode.

For more readings built on science, including original ones you are free to use, see our science and stardust readings for a non-religious funeral.

Sources

Freeman, A. (2005), NPR, All Things Considered: the commentary beginning "You want a physicist to speak at your funeral." Transcript.

Noether, E. (1918), Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen: "Invariante Variationsprobleme." The theorem linking conservation of energy to the laws of physics being the same at all times.

Cowan, C.L., Reines, F. et al. (1956), Science: "Detection of the Free Neutrino: a Confirmation." The discovery of the particle Pauli proposed in 1930 to keep energy conserved.

NASA Earth Observatory: "Climate and Earth's Energy Budget." How Earth balances the sunlight it absorbs by radiating infrared energy back to space.

Wald, G. (1968), Science: "Molecular Basis of Visual Excitation." Nobel lecture describing how light changes the shape of retinal in the eye.

Freitas, R.A. (1999), Nanomedicine, Volume I: an estimate of about 7 × 10²⁷ atoms in a 70 kg human body.

U.S. Energy Information Administration: average electricity use of a U.S. home, roughly 10,000 to 11,000 kilowatt-hours per year.