In this episode of The Interplanetary Podcast, I'm joined by my new co-host, singer-songwriter Leddra Chapman, as we tackle one of the most mind-bending ideas in all of science: special relativity. From the speed of light and the nature of causality to time dilation, the ether, and Einstein's revolutionary insight into space and time, we follow the story that changed our understanding of reality. And, as always, I can't resist ending with a slightly outrageous thought experiment of my own.

James Clarke Maxwell 

So where do we start.  So Einstein noticed something that even the greatest minds hadn’t only about 120 odd years ago.   And when you spot it it’s pretty trivial and obvious, the reality is only involves freshman maths (year 10 UK ish)

So let’s start with this simple observation, 

Imagine the Sun vanished. Not exploded. Not dimmed. Simply disappeared. Earth would continue orbiting an empty patch of space for eight minutes. 

• Not because gravity is weak.

• Not because Earth hasn't noticed yet.

• But because information about the Sun's disappearance cannot travel faster than light.

The gravitational field cannot update instantaneously.

The reason is one of the deepest truths in physics: information cannot travel instantaneously. The speed of light is not really about light at all. It is the speed of causality, the speed at which the universe itself updates.   If photons didn’t exist there would still be a speed of light!!,  

GW170817 was a gravitational wave (GW) observed by the LIGO and Virgo detectors on 17 August 2017, originating within the galaxy NGC 4993, about 140 million light years away. The wave was produced by the last moments of the in-spiral of a binary pair of neutron stars, ending with their merger. It is the first GW detection to be definitively correlated with any electromagnetic observation.  The aftermath of this merger was seen by 70 observatories on 7 continents and in space, a significant breakthrough for multi-messenger astronomy. The discovery and subsequent observations of GW170817 were given the Breakthrough of the Year award for 2017 by the journal Science

Gamma rays were detected about 1.7 seconds after the gravitational waves. Aha, you say see light and gravity are moving at different speeds, but if gravity and light travelled at noticeably different speeds, after 130 million years of travel you'd expect differences of maybe at least hours surely, That tiny delay is almost certainly due to the astrophysics of the explosion itself rather than propagation through space. 

• Two neutron stars spiral together.

• The merger generates a burst of gravitational waves.

• The stars collide.

• Matter is violently ejected.

• A jet forms.

• The jet punches through surrounding debris.

• Gamma rays are finally emitted

There is your 1.7 seconds ….that is a more violent explosion even than that rather unfortunate Blue Origin explosion this week.

Can you tell if you're moving?

This mega abridged classic Galileo passage comes from Dialogue Concerning the Two Chief World Systems and is often called Galileo's Ship.

Galileo realised something astonishing. Lock yourself below deck on a smoothly sailing ship. Watch flies buzzing, fish swimming in a bowl, or water dripping from a bottle. No matter how carefully you look, you cannot tell whether the ship is stationary or moving at a constant speed. Motion, Galileo concluded, is relative.

Three centuries later, Einstein would take Galileo's insight and apply it not to ships and pendulums, but to light itself.  But we’re jumping ahead of ourselves.

Before Einstein, people thought the speed of light might be a property of light. After relativity, and especially after GW170817, we know light isn't setting the speed limit at all.

Enter Maxwell

Maxwell discovered that electricity and magnetism are locked together in a cosmic dance. A changing electric field creates a magnetic field, and a changing magnetic field creates an electric field. The two chase each other through space, forming a self-sustaining wave. 

A guitar string has a natural wave speed determined by its tension and mass. Maxwell discovered that empty space appears to have its own wave speed too. It's almost as though the universe comes pre-tuned. If a guitar string's note depends on its physical properties, then perhaps the constants of nature are the tuning pegs of the universe. The analogy isn't perfect because spacetime isn't literally a stretched membrane in ordinary 3D space  

When Maxwell calculated the speed of that wave, he found something extraordinary: it was exactly the speed of light. Light wasn't something separate from electricity and magnetism. 

Here’s the big contradiction, Maxwell's equations contained no reference to the observer's motion. Maxwell's equations predicted a fixed wave speed, 

If I throw a tennis ball from a moving car, you simply add the speed of my throw to the speed of the car. That's how velocities normally work. So surely light should behave the same way? If I shine a torch from a moving vehicle, shouldn't the light travel at the speed of light plus the speed of the vehicle?

Maxwell's equations seemed to say no.

So perhaps we're thinking about it the wrong way. What about sound? If I'm sitting in a car and blast the horn, the sound doesn't behave like a tennis ball. The sound wave travels through the air at the speed of sound, regardless of how fast I was moving when I emitted it. In fact, if I drive fast enough, I can almost catch up with my own sound wave. That's what a supersonic aircraft is doing when it creates a sonic boom. But there's a crucial difference. Sound is travelling through a medium: air. The air defines what "at rest" means for the sound wave.

So perhaps light works the same way. Perhaps light is a wave travelling through some invisible medium that fills all of space. A cosmic substance that defines the true state of rest of the universe.

Have we solved the mystery?

Physicists certainly thought so.

They called it... the Ether. 

By the 1880s, physicists believed light travelled through an invisible substance called the ether, much like sound travels through air. If Earth was moving through this ether, then light travelling in the direction of Earth's motion should move at a slightly different speed from light travelling at right angles to it.

This is where Albert A. Michelson and Edward Morley come in.

Side quest: Michelson emigrated from Prussia (now Poland) to the United States as a small child and was raised in rough mining towns during the aftermath of the Gold Rush. Albert grew up surrounded by prospectors, saloons and frontier life rather than universities and laboratories. At 17, Michelson wanted to attend the U.S. Naval Academy. He lost the local competition for a place, travelled all the way to Washington, persuaded people to hear his case, and eventually received a special appointment from President Ulysses S. Grant himself, he effectively talked his way into the Naval Academy. Albert Michleson is the first American to win the nobel prize!!!

In 1887 they built one of the most sensitive scientific instruments ever constructed: an interferometer. They split a beam of light into two perpendicular paths and then recombined them. If Earth was moving through the ether, the two beams should take slightly different times to complete their journeys, creating a measurable shift in the interference pattern.

The result?

Nothing. 

• No ether wind.

• No preferred direction.

• No evidence that Earth was moving through any medium at all.

The experiment didn't merely fail to find the ether. It failed to find any evidence that motion through the universe itself could be detected.

BTW Einstein was still a teenager

Maxwell had an equation that predicted a fixed speed for light and here was an experiment that couldn't find the medium that speed was supposed to be measured against.

For nearly twenty years nobody had a satisfying explanation.

Physicists had reached an uncomfortable position. Galileo seemed right. Maxwell seemed right. Michelson and Morley seemed right. Yet all three couldn't be right at the same time

Then, in 1905, Albert Einstein proposed something radical:

The ether doesn't exist. The speed of light really is the same for everyone, and it is space and time that change to make this possible.

That sounds backwards because our intuition says:

Surely space and time are fixed, and the speed of light should vary.

Einstein realised that nature does the opposite.

Imagine interviewing every driver on Earth. No matter how fast their car was travelling, every single one insists they were travelling at exactly 60 mph. At that point you don't question the speed. You start questioning the clocks and the mile markers   The distance and time must be observer dependent, and that is sooo counter intuitive, that simple idea of treating speed as the constant and the distance and time as the variables is Einstein's true genius. 

speed=distance​ / time

If you really want the true insight here, the speed of light is constant, that Constant, C, is part of the geometry of spacetime itself.  Spacetime has a built-in conversion factor between space and time? 

Let’s re ask a question: How do you know you're moving? 

Imagine being sealed inside a windowless spacecraft.

Imagine a clock unlike any you've seen before. It has no gears, no springs, no batteries. Instead, a pulse of light bounces between two mirrors. Every time the light reaches the top mirror and comes back down, one second has passed. Now imagine you're sitting next to this clock on a spacecraft.

From your point of view, the light simply travels straight up and straight down.

But now imagine I'm watching your spacecraft fly past from Earth. From my point of view, while the light is travelling upward, the spacecraft is moving sideways.

So the light doesn't travel straight up and down. It travels in a zig-zag. In fact, the light has to travel further. And here's the problem. The speed of light is fixed.

Derive time dilation on a napkin

Einstein's entire argument rests on that fact.

• The light is travelling further, but it isn't allowed to travel faster.

Yes, Most physicists weren't ready to throw away the ether. Dutch physicist Hendrik Lorentz, proposed a clever rescue. Perhaps the Earth really was moving through the ether, but objects physically shrank in the direction of motion, hiding the effect. Remarkably, the mathematics worked. Lorentz derived the very equations that describe time dilation and length contraction. Einstein's genius wasn't discovering different equations. It was realising that the equations were telling us the ether didn't exist 

• So there is only one thing left that can change. The journey must take longer.

• And if the light clock takes longer to tick, then every clock on the spacecraft must take longer to tick. Not because the clocks are broken. Not because the machinery is faulty. But because time itself is passing more slowly.

• And the beautiful thing is that nobody on the spacecraft notices.

  • Their heart beats normally.

  • Their watch ticks normally.

  • Their thoughts occur normally.

• Only someone in a different frame of reference sees the difference.

• Now here's the beautiful part. Einstein's result doesn't require advanced mathematics. In fact, it drops out of Pythagoras' theorem.

• Imagine our light clock again. To the astronaut, the light travels straight up and down between two mirrors.

• But from Earth, the spacecraft is moving sideways while the light is travelling.

• That means the light traces out a diagonal path.

• And whenever you see a diagonal, Pythagoras is lurking nearby.

• Think of a right-angled triangle. The vertical side is how far the light travelled up. The horizontal side is how far the spacecraft moved sideways. The diagonal is the actual path the light took as seen from Earth.

• Pythagoras tells us that the square of the diagonal equals the square of the vertical side plus the square of the horizontal side.

• Now remember, light travels at the speed of light in both frames.

• So the length of each side is just light speed multiplied by time in that reference frame.

  • The diagonal becomes c times t.

  • The vertical side becomes c times t₀.

  • The horizontal side becomes v times t.

• That's just Pythagoras.

• Now move the terms around a little, factor out a t squared, and you get the famous result.

  

  
  

• The entire edifice of time dilation emerges from three ideas: First, motion is relative, as Galileo realised. Second, the speed of light is fixed, as Maxwell's equations seemed to imply. And third, a right-angled triangle.

One of the greatest ideas in science involves many great minds through history, Einstein was standing on the shoulders of giants. Galileo, Maxwell, and Pythagoras. - > Eintstein …It’s genuinely beautiful.

The famous light clock wasn't Einstein's original argument. But as a teenager Einstein had an equally strange question. What would happen if you could chase a beam of light? Maxwell's equations seemed to say that was impossible. Nearly twenty years later that simple question would help lead him to special relativity 

When we say clocks, we really do mean all clocks, absolutely everything measuring time.

If all clocks slow down together:

• watches,

• heartbeats,

• neurons,

• computers,

then nobody notices.

There is no experiment inside the spacecraft that reveals your absolute motion.

The actual reality is that information can only travel at the speed of light. Every known way that one thing can influence another appears to respect the same cosmic speed limit., be it a photon for electromagnetism, Gluon for the strong nuclear force, the bosons for the Weak Nuclear Force or the Graviton for gravity. 

As an aside if I have a button on the earth that send a radio message to switch a red light on the moon only knows it’s been pressed 1.3 seconds later?   But if I try to switch that red light on using a very long pole, can’t it be instantaneous?   

No. A perfectly rigid pole cannot exist. The push itself propagates through the atoms of the pole at a finite speed . through that material, a pressure wave propagating down the pole would actually take 18 hours!!!!!

Most people think the shocking thing about relativity is that time slows down.

It isn't. …The really shocking thing is that Einstein got rid of the idea of a universal "now." …I think this is one for another Podcast.

• We have already abandoned absolute motion.

• We have already abandoned absolute time.

• We have already abandoned absolute simultaneity.

But what if consciousness somehow reintroduced an absolute frame?

OK, so I promised you my own slightly crazy insight.

One of the biggest unsolved questions in science is consciousness. Not intelligence, not memory, but consciousness itself. Why is there a subjective experience of being you at all? Philosophers call this the "hard problem" of consciousness, and despite decades of research we still don't have a universally accepted answer.

Some theories, particularly dualism and certain forms of panpsychism, suggest that consciousness may not be entirely explained by the physics we currently understand. Even if that were true, it would still have to interact with the physical brain somehow, otherwise it couldn't create memories, influence decisions, or allow us to talk about our experiences.

So here's the thought experiment.

We know that relativistic motion causes biological and physical processes to slow down relative to an outside observer. Clocks slow down. Chemical reactions slow down. Neurons slow down. Everything slows down together.

But what if consciousness followed a different set of rules?

What if the biological clock dilated, but the conscious clock did not?

What if, at sufficiently high velocities, the coupling between consciousness and the physical brain began to break down in ways that evolution has never had to deal with?

I'm not suggesting this is true. There is currently no evidence that it is. But if it were, the consequences would be extraordinary.

Imagine an astronaut returning from a relativistic journey and reporting:

"I don't know how to explain it, but my subjective experience felt different. It didn't match what the clocks said should have happened.  I don't know how, but my subjective experience feels different above some velocity."

If this effect were reproducible, you've discovered something astonishing.

Not just a new aspect of consciousness, but a new physical observable.

You could build a "consciousness speedometer."

And the moment you can measure absolute velocity, you've identified a preferred frame of reference.

That would be comparable in significance to the discoveries of Isaac Newton, Albert Einstein, and the founders of quantum mechanics.

I'm not claiming this is true. I'm claiming that if it were true, the consequences would be extraordinary.   Of course if I were a deluded narcissist I could go on Joe Rogan and he’d lap it up.

Galileo Galilei:  "Measure what is measurable, and make measurable what is not so."   What if consciousness could measure something we currently think is unmeasurable? 

Most scientists think consciousness emerges from ordinary brain activity. Roger Penrose and others disagree. Penrose argues that consciousness may depend on a deeper layer of physics that we don't yet understand. If he is right, then understanding consciousness may ultimately require new physics in the same way that understanding atoms required quantum mechanics, Together with Stuart Hameroff, he proposed the Orchestrated Objective Reduction (Orch-OR) theory. The idea is that tiny structures inside neurons called microtubules may support quantum states. Penrose suggested that these states undergo a special type of collapse related to gravity itself.

• Relativity says clocks dilate.

• What if consciousness doesn't?

• That would imply consciousness has its own clock.

• A separate clock could identify absolute motion.

• Therefore consciousness could reveal a preferred frame.

If consciousness contains an aspect not governed by relativistic time dilation, then conscious observers could in principle distinguish between states of uniform motion. Such an ability would constitute evidence for a preferred frame of reference and imply that current physical theories are incomplete. 

Oh this is all special relativity because it talks only about going at a constant velocity, if you want i more generalised, then Einstein has you covered …you guessed it with general relativity.

"The speed of light isn't the speed of light. It's the speed at which the universe allows one event to influence another."

Einstein once said, 'No amount of experimentation can ever prove me right; a single experiment can prove me wrong.' If one day consciousness turns out to be a speedometer for the universe, Einstein's theory will need revising. Until then, a button pressed on the Moon doesn't become a fact on Earth for 1.3 seconds