The Self-Propagating Wave
The standard account of how light travels, examined. Not disputed — examined.
That description has a familiar shape. Energy passing back and forth between an electric form and a magnetic form is a tuned circuit, and free space has the quantities to be one: a capacitance per metre, an inductance per metre, an impedance of 376.73 ohms, and a wave speed that follows from the first two. Radio engineers calculate with it that way every day. What free space does not have is a resistance — and every tuned circuit ever built rings down and stops.
The reason it has none is that one part of its permittivity is written as zero. Nothing in the theory requires that; it is set to zero because no absorption has ever been observed. The observation and the assumption are the same thing wearing different clothes.
None of this disputes a single prediction. The standard account is arguably the most thoroughly confirmed description human beings possess, and every number in this memo comes out of it correctly. The claim is narrower: where it is asked why — why nothing is absorbed, what the field is a field of, where the energy is while in transit — it does not answer, and says so itself when pressed.
What this memo does and does not do
It examines the standard account of how light travels and shows that three of its features — the losslessness, the absence of a substrate, and the location of energy in transit — are recorded rather than derived.
It disputes no prediction and identifies no error. Nothing here is a refutation, and section 8 says so at length. The alternative account in this series carries the same debt on the first of the three, and a larger one.
Draft. A working draft, published for scrutiny rather than as a settled result.
This memo does not claim the standard account is wrong. It reproduces every measurement ever made, to every precision anyone has reached, and section 8 says so plainly. What is examined here is the difference between describing something and explaining it.
1. What The Account Actually Says
Ask how light crosses empty space and the answer given since 1865 is this. A changing electric field creates a magnetic field. That magnetic field, itself changing, creates an electric field. The two take turns, each making the other, and the pair travels outward at 299,792,458 metres per second.
There is nothing underneath. The fields are not disturbances in anything. They are the thing itself, as basic as matter, and no substance is required or proposed.
Take it seriously before examining it
This is not a fudge or an evasion. It is the most successful description in the history of science. It predicts the colour of a sodium flame, the behaviour of every radio, the working of every lens, and the figures in the memo you are reading — all to as many decimal places as anyone has cared to check.
Nothing in this memo contradicts any of that. The question asked here is narrower: when the account says the fields sustain each other with nothing underneath, what is being claimed, and is it an explanation?
2. That Description Is A Tuned Circuit
Energy passing back and forth between an electric form and a magnetic form is not an unusual arrangement. It is the commonest circuit in electronics, and it has a name.
In a tuned circuit, charge sloshes between a capacitor, which stores energy electrically, and a coil, which stores it magnetically. Each drives the other, and the energy passes back and forth at a rate set by how big they are. Every radio ever built contains one.
Free space has both quantities and they have been measured.
| Property of free space | Value | What it is |
|---|---|---|
| Capacitance per metre | 8.854 × 10−12 F/m | how much electric energy it holds |
| Inductance per metre | 1.257 × 10−6 H/m | how much magnetic energy it holds |
| Impedance | 376.73 ohms | what it presents to a wave |
| Wave speed from those two | 299,792,458 m/s | the speed of light |
| Resistance per metre | zero | assumed, not measured |
Radio engineers treat free space exactly this way, every day, when they design antennas and feedlines. It is not a loose comparison. It is the same calculation.
3. Every Tuned Circuit Ever Built Rings Down
Strike a tuned circuit and it rings, and then it stops. How long it lasts is measured by a number called Q: roughly, how many oscillations before the energy has mostly gone.
| Circuit | Oscillations before it fades |
|---|---|
| A radio tuning circuit | about 50 |
| A quartz watch crystal | 100,000 |
| An atomic clock cavity | 1,000,000,000 |
| The best superconducting cavity ever built | 1011 |
| Light in free space | it never stops |
How far that gap really is
Light from a distant quasar has been oscillating for thirteen billion years. At its frequency that is more than 1032 oscillations, and it arrives at close to the brightness expected.
The finest resonator human beings have ever constructed — a superconducting cavity cooled to near absolute zero — manages 1011. Free space outperforms it by twenty-one orders of magnitude, and there is no upper limit on the figure because no loss has ever been detected at all.
4. Why This One Does Not
The answer is in how the two constants are written.
For any material that absorbs light — tinted glass, seawater, a brick — the permittivity has two parts. One part describes how the material holds the field. The second part describes how much it takes out of the wave, and that second part is the absorption. Every absorbing material has one.
For the vacuum the second part is written as zero.
That is a decision, not a discovery
Nothing in the theory requires the second part to vanish. It is set to zero because no absorption has been observed, and once set to zero the equations say light travels forever without loss. The observation and the assumption are the same thing wearing different clothes.
So the account does not explain why light never fades. It records that it does not, and builds the record into the starting conditions.
This is worth stating carefully, because the alternative account is in the same position. The Aether version needs a medium so nearly frictionless that nothing has ever come within twenty-four orders of it, and it cannot derive that either. Neither side has an answer. One side calls it a definition and the other calls it a requirement.
5. A Field Of What?
The word field is used elsewhere in physics and it always takes an of. The temperature field of a room. The velocity field of a river. The pressure field of the atmosphere. In every case the field is a set of values describing the condition of something, at each point of it.
The electromagnetic field is the one case where the of is dropped. It is not the electromagnetic field of anything. It is simply the field, and that is held to be a complete answer.
This may be the right answer
There is a serious position here, not an evasion. It says the demand for an of is a habit of mind carried over from fluids and ropes, and that at bottom the world may simply be made of fields rather than of stuff. Asking what a field is made of might be like asking what a number is made of.
The difficulty is that it cannot be tested. It is not a prediction that could come out wrong. It is a decision about where to stop asking, and the decision was made because the previous answer — a mechanical medium — ran into trouble in 1887 and was set aside.
6. Where Is The Energy In Between?
Light leaves a quasar. Thirteen billion years later it enters a telescope. Between those two events it was not in the quasar and not in the telescope.
The same question in a sharper form: in 2015 two black holes merged and radiated the equivalent of three Suns as gravitational waves — 5.4 × 1047 joules. That energy left the source 1.3 billion years ago and moved mirrors in Louisiana. For 1.3 billion years it was in transit.
And the theory cannot say where it was
This is the part most people do not know. General relativity has no way to say how much gravitational energy is at a given place. There is no proper quantity for it — only approximations that can be made to vanish entirely by choosing a different set of coordinates.
So the standard account holds that the energy was definitely transported and definitely cannot be located while travelling. That is a strange thing to say about a quantity everyone agrees is conserved, and it has been a recognised difficulty since the 1910s.
7. Four Things The Vacuum Does
A genuinely empty space would do nothing at all. Empty space has been measured doing four things.
| What happens | Since | Why it is odd |
|---|---|---|
| Light scatters off light | 2017 | In classical theory two beams pass through each other with no effect whatever. They do not. |
| Charge changes strength with distance | measured at colliders | Close up an electron’s charge is stronger than far away, because the vacuum around it responds. Nothing cannot respond. |
| Two uncharged plates attract | 1997 | With no charge, no field and no contact, they still pull together. |
| The hydrogen spectrum is shifted | 1947 | The electron’s energy levels are moved by something acting on it in the gap. |
The question this leaves
The standard account accepts all four and describes them as effects of the vacuum having a lowest energy that is not zero. On that view space is not empty at all — it is full of fields in their ground state, seething.
So both accounts agree that something is there. They disagree about what to call it and how far to press the question.
And it leaves a very specific puzzle. The vacuum interacts with light — measurably, four ways — and never takes any energy from it. It responds without absorbing. Nothing else behaves that way, and nobody explains why this does.
8. What The Account Gets Right
All of it.
Every prediction in this memo, every number in the tables, the speed of light, the impedance of free space, the behaviour of every antenna, the colour of every star — all come out of the standard account correctly, to as many decimals as anyone has measured.
Why that has to be said plainly
A memo of this kind can easily be read as claiming physics has made a mistake. It has not. The electromagnetic theory of light is arguably the most thoroughly confirmed thing human beings know.
The claim here is narrower and it is not a criticism of anyone. The account describes what light does with complete accuracy, and where it is asked why — why nothing is absorbed, what the field is a field of, where the energy is while in transit — it does not answer, and it says so itself when pressed. Describing is not the same as explaining, and a theory that does the first superbly may still owe the second.
9. What Would Settle It
- Deriving the losslessness from something — either account — rather than writing it into the starting conditions. Whichever side managed it first would have a real result.
- Finding any absorption at all. A single measurement of light losing energy to the vacuum would change the picture completely. None exists, and the bound is one part in 1026 per metre.
- Locating the energy of a wave in transit. For light this is straightforward; for gravity it is not possible within the present theory, and a method would be a significant advance.
- A demonstration that the vacuum does nothing to light. This would remove the puzzle in section 7 entirely. The measurements run the other way — four of them.
10. The Numbers
In summary, the figures behind the argument:
- Capacitance of free space: 8.854 × 10−12 F/m. Inductance: 1.257 × 10−6 H/m. Resistance: zero, assumed.
- Oscillations before the best cavity ever built fades: 1011.
- Oscillations of light from a distant quasar, still arriving: more than 1032.
- Energy in transit from one black hole merger: 5.4 × 1047 joules, for 1.3 billion years.
- Measured things the vacuum does to light, charge and atoms: four.
- Predictions of the standard account that this memo disputes: none.
Terms Used Here
| Word | What it means |
|---|---|
| Aether | The proposed substance filling all space: one kind of particle which light would travel through and which matter would be built from. Not an established entity — the memos set out what would have to be true for it to exist. |
| Sideways wave | A wave where the material moves across the direction of travel, like a shaken rope. Light is one. |
| Polarisation | The orientation of a sideways wave. Polarised sunglasses block one and pass the other. |
| The Casimir effect | Two uncharged plates in a vacuum attract each other. Measured since 1997, and direct evidence that empty space is not empty. |
| “Empty space” | A misleading but unavoidable phrase. The space between the stars is not empty. What is genuinely empty is the void — the room the Aether occupies, which has no properties at all. |
| Deep space | The Aether far from any matter, at its natural density of about 0.9 kg per cubic metre. |
| Q | How long an oscillation lasts before it fades. A radio circuit manages about fifty; the best laboratory cavity 1011. Light in space has never been observed to fade at all. |
| Light scattering off light | Two beams crossing should pass through each other with no effect. They do not. Measured at the Large Hadron Collider in 2017. |
Every term used across the series is on the terms page.
11. Sources
Reference codes read source.work.passage and resolve on the Master Source Register, which carries every source used across this series.
- Bureau International des Poids et Mesures. The International System of Units (SI), 9th edition (2019). The constants in sections 2 and 10. 72
- J. C. Maxwell. A Dynamical Theory of the Electromagnetic Field, Philosophical Transactions (1865). The account stated in section 1. 79
- ATLAS Collaboration. Evidence for light-by-light scattering in heavy-ion collisions, Nature Physics 13 (2017) 852–858. Carried as reported; not verified against the original.
- W. E. Lamb & R. C. Retherford. Fine Structure of the Hydrogen Atom by a Microwave Method, Physical Review 72 (1947) 241. Carried as reported; not verified.
- S. G. Lamoreaux. Demonstration of the Casimir Force in the 0.6 to 6 µm Range, Physical Review Letters 78 (1997) 5. Carried as reported; not verified.
- B. P. Abbott et al. Observation of Gravitational Waves from a Binary Black Hole Merger, Physical Review Letters 116 (2016) 061102. The energy figure in section 6. Carried as reported; not verified.
- On the absence of a local energy density for the gravitational field: standard in the general relativity literature since the 1910s. Not individually sourced; the point is uncontested.
Verification register: references 3 to 6 are carried as reported from secondary sources and have not been checked against the originals. Reference 3, the light-by-light scattering result, is load-bearing for section 7 and should be read before publication. The Q figures in section 3 are order-of-magnitude values from the resonator literature, not precise measurements of specific devices.
Ledger — memo D.9
- Derived
- That the standard description of a self-sustaining wave is, term for term, the description of a tuned circuit — free space has a capacitance, an inductance and an impedance, and its wave speed follows from the first two
- That the losslessness follows from setting one part of the permittivity to zero, which is an input rather than a result
- Measured
- The permittivity, permeability and impedance of free space
- Light-by-light scattering (2017), the running of charge strength, the Casimir force (1997) and the Lamb shift (1947)
- The energy radiated by GW150914 and its 1.3-billion-year transit
- Q figures for laboratory resonators, and the absence of any detected absorption in space
- Assumed
- That describing and explaining are different things. This is a philosophical position, not a physical result, and a reader may reasonably hold that a complete description is an explanation. If so, this memo has no force.
- That the demand for a substrate is legitimate. Section 5 states the case against, and does not answer it.
- Open
- Why nothing is ever absorbed. Neither account derives it. This is a debt on both sides and the Aether account’s version is the larger one — it needs a medium twenty-four orders less lossy than anything ever built
- Where the energy of a wave in transit is located. Answerable for light, not answerable for gravity within the present theory
- Why the vacuum interacts with light without ever absorbing from it. Four measured interactions, no dissipation. Nobody explains the combination
- Whether the tuned-circuit reading of section 2 is more than an accounting identity. The quantities match exactly; whether that means anything is the question the memo raises and does not close
- Prior art
- Maxwell (1865) — the account examined here, in its original form
- Lamb & Retherford (1947), Lamoreaux (1997), ATLAS (2017) — the four measured effects of section 7, none of them obtained by anyone arguing for a medium
- The transmission-line treatment of free space in section 2 is standard radio engineering and is not original here