I'm writing a science fiction story set in a future where aliens have made contact with us and established interstellar trade. I'm trying to invent a fairly believable universal standard unit of measure that both humans and aliens could use. I've been thinking about using the speed of light, which is currently inseparable from our local units of length and time. This unit of measure is the plot device which allowed these aliens to communicate with us and build the QM information link, thereby enabling interstellar coordination of shipping.

So I'm not sure how to express it in terms of TIQM information transaction cycles, but I think that’s a believable place to have one for the storyline.

TIQM stands for Transaction Interpretation of Quantum Mechanics. My unit of measure relies on the speed of information transfer - an admittedly weird language for waves traveling through time- , which follows the light cone in both directions (the advance wave and retarded wave), known as a Wheeler–Feynman handshake or transaction; the waves having coincidence at the present moment. So the principle for my fictional unit is basically that TIQM turns out to be the correct interpretation, and these aliens have figured out a way to make a universal measure of distance using the distance a photon of light travels during the time of one “echo” of the wave traveling source to destination. I’ll give it a name “Quanton” distance and most objects would be measured in large multiples of it, such as EtaQuantons.

I’m looking for help articulating the theory with accurate enough language to live in the unknowns while not blatantly contradicting known TIQM principles.

How could my aliens represent a universal measurement with the TIQM Wheeler-Feynman Handshake?

Note: this is the opposite question asked about the ansible here because that question explicitly omits quantum entanglement as the mechanism, I am relying on the TIQM interpretation entanglement to build my ansible.

The story:

Per comments, I thought it would be useful to include the dialogue of my characters. An answer simply fills in the blank in this scene with something not ridiculous.

"I can't believe it," said Dr. Smith, staring at the computer screen in disbelief. "They’ve solved the transaction interpretation of quantum mechanics."

Her colleague, Dr. Jones, came over to look at the screen. "What is it?" he asked.

"It's a universal unit of measure," Dr. Smith said. "A unit of measure that applies to everything in the universe, from the smallest subatomic particles to the largest galaxies."

"That's incredible," Dr. Jones said. "How did they do it?"

"It must have been a long and difficult process," Dr. Smith said. "But it appears the key was indeed to think of quantum mechanics as a transaction of information between two objects. However they proved this, everything soon fell into place."

Dr. Jones shook his head in amazement. "This is going to change everything," he said.

"I know," Dr. Smith said, turning sullen now. "It's the breakthrough that quantum mechanics is waiting for."

Dr. Jones paused with a puzzled look on her face. “What do you mean ‘is waiting for?’ Didn’t they share the solution?”

“We can now measure with the universal constant. They gave us little more than that.”

“Can I see the paper?” Dr. Jones took the paper from Smith’s unenthusiastic hands and began reading.

“Photons exist at the junction of two waves traveling in opposite directions through time, from the source to the destination; and vice versa. All particles do, in fact. However, photons propagate through the space portion of spacetime at an exact velocity, thereby allowing the elimination of the velocity vector from a calculation. But further, the information they sent suggests that the propagation of the waves through the time structure of spacetime is not variable, it is also a constant. Thus, the only variable remaining is distance. It can not vary, and is exact. All that remained to define a constant was ___________. This, they have found.”

  • $\begingroup$ I don't get it, with the "echo" of a QM fluke, is it constant regardless of destination? And yes, instead agree on a time unit small enough to use c*t as a means of standard length. $\endgroup$
    – Vesper
    Aug 21, 2023 at 15:14
  • $\begingroup$ TIQM creates a new “conservation of information” (my own phrase) to solve the unjustifiable spontaneous waveform collapse (WC) of two photons separated by an unlimited distance. WC violates the causal light cone (or appears to) and the Copenhagen interpretation just explains this as magic, no mathematical causal relationship to its own dictums. The (real) TIQM eliminates that and other paradoxes. The aliens improved the TIQM by studying advance and retarded waves, thus discovering a universal length. Yes, my world assumes the TIQM-derived constant completely ignores source and destination. $\endgroup$
    – Vogon Poet
    Aug 21, 2023 at 16:17
  • $\begingroup$ After reading the snippet of the story and the introduction to the TIQM interpretation of Quatum Mecahnics, I am confused about one point. Are you assuming in our world that information travels at a different speed than light does? $\endgroup$
    – Chuu
    Aug 21, 2023 at 19:25
  • $\begingroup$ No, wave-function collapse and the retrocausality paradox in the Copenhagen interpretation lead to TI. The observed simultaneous state changes in discreet particles are explained in TI as a coincidence of two waves: (retarded/advance waves) the first from the past to the future; and the latter from the future to the past. These waves meet in the present, exchanging only state information. Wavefunction collapse never happens, information across the wavefunction is merely conserved, classical violations are avoided. TI relies on observations; not assumptions about our world or the speed of info $\endgroup$
    – Vogon Poet
    Aug 21, 2023 at 22:43
  • 1
    $\begingroup$ Thank you for the compliment, but I really don’t think the acid blood is as stupid and boring as you suggest. Nonsensical, sure. When I write the final draft I’ll keep this in mind… world first however. $\endgroup$
    – Vogon Poet
    Aug 25, 2023 at 21:36

3 Answers 3


Start with Planck Units

  1. c = Speed of light = 1 (property of light, aliens can measure)
  2. G = Gravitational Constant = 1 (property of matter, aliens can measure)
  3. ℏ = Reduced Planck Constant = 1 (relationship of light's energy and frequency, aliens can measure)
  4. k = Boltzmann Constant = 1 (property of matter, specifically gasses, aliens can measure)

If you start out with these, you can define other things like length, time, mass, and temperature. Length, time, and mass can all be derived from c, G, and ℏ. Boltzmann constant is needed to define temperature.

Specifically your question about length would be answered by the Planck length which is defined as $l=\sqrt{\frac{\hbar G} {c^3}}$

What this means is that the speed of light isn't actually inseparable from our local units of length and time, you're just used to seeing it expressed with our local units.

The reason this is the best answer is that the Planck units are not at all human-centric. So unless the aliens come from a place where physics works differently (like gravity being stronger in their part of the universe), it should be relatively simple to establish a basis for communication.

Alternatively (but the same principle)

Just tell them, in our units, what are the speed of light, gravitational constant, and the Planck constant. With that information they can, with some effort, convert it into any other system. It might be easier to fold into the rest of your story that way. It could also work if they told us those things in their units and let us work it out.

  • $\begingroup$ Could you please hilight the portion that they have discovered - the fictional component? My Q was trying to use a TIQM derivation but obviously there’s more than one way to skin a cat. Thanks for the idea. $\endgroup$
    – Vogon Poet
    Aug 21, 2023 at 17:07
  • $\begingroup$ Also, an answer without TIQM puts a big hole in my ansible argument that I will have to rewrite, unless it also can avoid the Copenhagen interpretation. W-F handshake conveniently opens the door to both my problems, made for a simpler story. $\endgroup$
    – Vogon Poet
    Aug 21, 2023 at 17:38
  • $\begingroup$ At the moment, there is really no evidence for or against the W-F handshake. Bell's experiments show that the polarisation of a photon is not predetermined, but decided when the first of two photons meets a polariser. This then needs some really spooky action at a distance and backwards in time to make sure this all happens without any total loss of energy or particles, and with no leftover bits when you absorb a particle. The Copenhagen interpretation still holds: we do not see any actual leftover quantum bits, or net losses or gains in energy. But 'how' is very much up for grabs. $\endgroup$ Aug 22, 2023 at 12:07
  • $\begingroup$ @VogonPoet Wow, the question has changed a lot since yesterday. I made an edit that might help story writing. Keep in mind, when you ask a question with the physics tag, try not to be disappointed when real world physics contradicts what you've imagined. $\endgroup$
    – Mathaddict
    Aug 22, 2023 at 15:58
  • $\begingroup$ I just looked back at my history and the only thing I changed was to add actual storyline dialogue, and disambiguate who was initiating the contact because it seemed to be misleading answers. $\endgroup$
    – Vogon Poet
    Aug 22, 2023 at 16:19

We currently measure time to one part in 1018 using an optical lattice clock. We could describe how to make one of these if we have the bandwidth. If bits are precious, we just need to specify Strontium by its atomic number. The beings at the other end ought to be able to figure out the rest.

Heck, if they have figured out a way of getting information back out of quantum coupling, I have a few questions for them, myself.

  • $\begingroup$ Are you answering how we would initiate communication with them? My Q is about them solving a TIQM formulation which predicted and lead to the discovery of a universal measurement. It was this measurement which enabled them to give us instructions to construct our half of the ansible. So the aliens have already figured it out, and they haven’t necessarily shared it with us, but only gave us their universal measurement derived through the Wheeler-Feynman Handshake, assuming TIQM is correct and they completed it. I’ll put more detail in the Q. $\endgroup$
    – Vogon Poet
    Aug 21, 2023 at 15:35
  • 1
    $\begingroup$ Probably add exact isotope, say 87, as they really differ in use and exact frequency of observed resonance. This couls also work to verify that we are speaking about periodic system, and this is not just a random number. Also adding difference to Cs-133 would help them narrow the means of those numbers even further. Like in: "55 133 1 38 87 46692,61371163061391721557013917" (the number is frequency of Sr-77 divided by frequency of Cs-133). $\endgroup$
    – Vesper
    Aug 21, 2023 at 15:36

Straightforward frame challenge:

the speed of light, which is currently inseparable from our local units of length and time.

This statement is false - we can give them our exact units with no reference to local processes. One second is 9192631770 times the period of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the isotope with 55 protons and 78 neutrons. One meter is one second times the speed of light, divided by 299792458. See: Caesium Standard, International System.

Of course, if there's interstellar trade, we can just Planet Express them a meter stick.

  • $\begingroup$ There isn’t interstellar trade until they sent this standard to us. A universal standard requires MUCH more than simply universality and scalability before it is useful in communication. Your example is HORRIBLE for its reproducibility, intuitiveness, and transmissibility. Their message will begin with only numbers, then a pattern of them. One of Sagan’s rare talents was his ability to remove his own anthropomorphism from the problems he challenged. “Neutron”, “proton,” “ground state,” and almost everything you said would be understood by pure chance unless they were human. We’re still looking $\endgroup$
    – Vogon Poet
    Aug 24, 2023 at 15:34

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