No One Has Measured The Speed Of Light: Let me prove it
I know what you are thinking.
-click bait
No one has measured the speed of light. That feels insane now that we are talking about it. It’s ridiculous. The speed of light is exactly 299,792,458 meters per second. We are so sure of it that since 1983, we’ve actually used the speed of light to define how long a meter is. It’s just the distance light travels in a vacuum in 1/299,792,458th of a second. That definition ensures that the speed of light is exactly this number,
no decimals.
But wait, in this article I will prove to you that light may never actually travel at this speed and I can say that because no one has actually measured it.
We can not measure the speed of light the same we measure the speed of anything else. So let’s talk about measuring the speed of anything and everything.
How can we measure the speed of the baseball fired out of a canon?
To get the speed of the baseball we need to know two things, we need to know
the distance between two points and the time that the baseball takes to travel from one point to another. Then we just divide the distance with time.
But here lies the question, can we measure the speed of light in this way?
SOLUTION NO:1
Imagine you have a laser that can fire a beam through a perfect vacuum for one kilometre. Start a timer the instant you fire the laser beam and then exactly when it hits the end, stop the clock. Except how do you even know when light reaches one kilometre if you and the clock are at the starting point?
SOLUTION NO:2
Okay, so you need two clocks, one at the laser and one at the end, which stops automatically when it detects the laser light. But now, how do you make sure your two clocks are synchronized?
SOLUTION NO:3
Well, you could connect them via a wire and send a pulse from one to the other, but that pulse will travel at the speed of light, so it will arrive with a time delay. You might think you can just subtract that time delay but it is equal to the time it takes for light to travel one kilometre. That’s what we don’t know and are trying to measure.
SOLUTION NO:4
Okay, new plan, start with the clocks together and sync them up first and then send one of the clocks down to the end. Now, what could possibly go wrong? Well, I’ll tell you. The clock at the finish line was moving
with respect to the one at the start and special relativity tells us moving clocks ticks slow relative to stationary observers. So by the time the clock reaches one kilometre, it will no longer be in sync with the clock at the start.
Can I tell you the solution to this problem?
SOLUTION NO:5
Ditch the second clock. Put a mirror at the end to reflect the light back and use a single clock at the start to time the full two-kilometre round trip.
- “But wasn’t this done before?”
My brother commented on this while on the call.
- “Someone was on a mountain and there’s a wagon wheel with a lantern and there’s something like a mirror on the other side of the mountain? I have always wanted to do this!”
So that sounds like how the speed of light was first experimentally measured by Hippolyte Fizeau in 1849. He shone a beam of light between the teeth of a rapidly spinning gear to a mirror up on hill eight kilometres away.
And then by increasing the speed of the gear, he reached that point where the reflected light passed through the next gap on the gear and so it was observed. So he measured the speed of light to be 313,000 kilometres per second, which is within 5% of the presently accepted value.
So someone has measured the speed of light? or have they?
What has been measured is the round trip or two-way speed of light, but no one has measured the one-way speed of light.
One thing I’m gonna throw at you. And I’m just gonna come out and tell you.
It’s like what if the speed of light in A to B direction is different from the speed of light in B to A direction? The question is could you figure it out?
The kind of the crux of this problem is that the only way people have managed to measure the speed of light is for a round trip. No one’s ever managed to measure the speed of light in just one direction.
It’s possible that the speed of light is half of ‘c’ in one direction and the instantaneous on the return journey.
Think about communicating with an astronaut stranded on Mars. Let’s call him…Mark. We send out a signal and get a response 20 minutes later. So we imagine our signal takes 10 minutes to get there and the reply takes
10 minutes to come back. But it’s possible that our message took all 20
minutes to get there and the reply came back instantaneously. There’s no way we could tell the difference between these two scenarios.
But why would the speed of light be different? Well, there may be some preferred direction through spacetime. I mean, our universe has a lot of symmetries, but there is also some asymmetry. For example, why is there so much matter relative to anti-matter? And physicists have worked out internally consistent theories of physics in which the speed of light is different forwards and in reverse. The speed of light could vary by just a few per cent up to at the extreme, going’ over two in one direction
and infinitely fast in the other direction.
Now, you might think it is just simpler that light should travel at the same speed in all directions, but the truth is: that is a convention rather than an experimentally verified fact.
Einstein himself pointed this out in his famous 1905 paper, On the Electrodynamics of Moving Bodies.
He spends the first couple of pages on the problem of synchronizing clocks at different locations A and B. And he says there is no way that we can meaningfully compare the times they measure unless we established by definition that the time required by light to travel from to B equals the time it
requires to travel from B to A. He’s essential defining that the speed of light in opposite directions is the same. And he puts by definition,
in italics to remind us that this is only a convention. It’s known as the Einstein synchronization convention.
So the idea that the speed of light is the same in opposite directions as Einstein would later write is
“neither a supposition nor a hypothesis about the physical nature of light, but a stipulation that I can make of my own free will to arrive at a definition of simultaneity.”
That sounds a lot more subjective than how I think most people would imagine the speed of light is defined. I didn’t think about this before. I always assumed that when we said the speed of light is c, we meant the one-way speed of light. There’s no way to define the one-way speed of light, so the only thing we can really define is the two-way speed of light.
Just look at the way Einstein defined c.
It’s for the round trip from A to B and back. I don’t know if you saw on your physics classes, but whenever there was a light clock it would always bounce the
light up and then back. You would never see a light clock just bounces light one way. And this is why the only thing we can be certain is constant for all inertial observers is the two-way speed of light.
For over 100 years, scientists have tried to find a way around this to measure the one-way speed of light by itself. Here is a paper
published in the American Journal of Physics in 2009 that claims to measure the one-way speed of light. And here is the paper
debunking this study, pointing out that these authors were actually measuring the two-way speed of light.
But I’m imagining you might have some ideas for how to measure the one-way speed of light, so let’s go through some of them.
I mean, can’t we just use a high-speed camera that shoots at a trillion frames seconds owe can actually see light passing through an object?
The problem is you’re not only seeing the light pass through the object, but you’re also seeing it bounce back to the camera, measuring the two-way speed, not one way.
What if you center a synchronizing device between your two clocks and send out simultaneous pulses? Well, if the speed of light is the same in both directions, this perfectly synchronizes your clocks. But if the speed of light is different in each direction,
one of the clocks will be ahead of the other. And it will be ahead by just the right amount so that when you measure the speed of light, you’ll find the value to be c, even though that was not the speed the light was travelling. This is the same reason GPS synchronized clocks won’t work.
The whole GPS system is based on the assumption that the speed of light is the same in all directions. If the speed of light is different in different directions, the light pulses from satellites will travel at different speeds so the clocks won’t properly be synced.
By that, I mean they will always measure c for the one-way speed of light whether it is or isn’t.
How about starting with synchronized clocks in the middle and moving them apart with equal and opposite speeds? That way, the time dilation for each clock will be the same and they’ll still be synchronized when they reached the endpoints. But again, this only works if the speed of light in each direction is the same.
If the speed of light depends on direction, then so does time dilation. You might think you could move the clocks really, really slowly so that time dilation is negligible.
But if the speed of light is different in different directions, you can’t just use the standard formula
to calculate what that time dilation would be. I mean, it could be a lot worse than you think.
So, the reality is we’re stuck. We need synchronized clocks to measure the one-way speed of light, but we need to know the one-way speed of light to synchronize our clocks.
Now, this might sound like just an academic concern, so I want to go through an example to illustrate just how different, the universe speed of light is not the same in all directions.
Let’s say on Mars, Mark is trying to synchronize his clock
with the Earth. At noon, mission control sends out a message that says “This signal was sent at exactly 12 o'clock”. When Mark receives this message, he uses the Einstein synchronization convention to set his clock. He knows the round trip time delay is 20 minutes, so he assumes the signal must have 10 minutes to reach him. He programs his clock to 12:10 PM and sends a return message, “Reply sent at 12:10”. The message is received on Earth at 12:20 PM, so both parties know the synchronization was successful. When the clock reads 12:20 on Earth, it simultaneously reads 12:20 on Mars. But now consider what happens if the speed of light is not the same in both directions.
Let’s say it is ‘c’ over two from Earth to Mars, and then instantaneous from Mars back to Earth.No one knows this, of course, so they continue to use the Einstein convention. The message is sent from Earth, but now it takes a full 20 minutes to reach Mars. But Mark doesn’t know this.
And as before he assumes the signal took 10 minutes to reach him, so he sets his clock to 12:10 PM even though on Earth, it is now 12:20. Mark then sends this reply sent at 12:10 PM, which is instantaneously received on Earth at 12:20 Earth time. The experience for the two communicators is the same. The same messages were received with the same local time delays, but their clocks are out of sync by
10 minutes. What they think is the same moment for the other observer actually isn’t and there is no they can ever recognize or correct this error. Imagine if someone on has immediately responded how long did this message take to reach you? It’s now 12:20.
Well, the message would take 20 minutes to reach Mars, but due to the clocks being out of sync, it would arrive at 12:30 Mars time,so Mark would reply 10 minutes,
a message that would instantaneously reach the Earth at 12:40 Earth time. The space-time diagram shows there is flexibility in what you consider to be the same moment at two different locations and in how you define the one-way speed of light. Einstein chose the convention where the one-way speed of light is always
the same, but from an experimental perspective, any other convention is just as valid, up to and including one where the speed of light is C over two one way and
instantaneous the other way.
And in that case, it’s interesting to think about what each observer is seeing when they look at the other.
Mark would be seeing the Earth has it was 20 minutes ago,
but Earth is seeing Mars in real-time exactly as it is right now.
And this effect wouldn’t stop at Mars, look beyond it and you could see
stars hundreds of light-years away, not as they looked centuries ago, but exactly as they are right this instant. One of the things is you only know about that light when it reaches you and you don’t know anything about what journey it took to get to you. You just see it and it’s there, so like it’s instantaneous.
So an instantaneous interpretation of that light is just as good as one where it takes ‘c’ to reach us. It is kind of unknowable, isn’t it? we’ve all agreed and this is based on something Einstein wrote in 1905, We’ve all agreed to just say it’s ‘c’ in every direction
but the truth is the physics works the same whether it’s ‘c’ or ‘c’ over two and instantaneous or anything in between. As long as the round trip works out to be ‘c’, none of the physics breaks and that’s the crazy thing.
So if we can ever measure the one-way speed of light, and if it makes no difference to any of the laws of physics, then what’s the point in even talking about it?
Well, that is certainly one valid perspective in a debate that has been ongoing since 1905. Some physicists appeal to Occam’s razor.
Isn’t it just simpler if light travels at the same speed in all directions? Most working physicists just accept the convention and move on with their lives, but I think it’s important to point out that it is just a convention, not an empirically verified fact.
Personally, I find it fascinating that this is something about the universe that is hidden from us.
Sure, the round trip speed of light is ‘c’, but does the one-way speed even have a well-defined value? And if it doesn’t, what does that mean for the concept of simultaneity? When is right now on Mars? Does it even make sense to talk about things happening at the same time if they’re separated by distance?
I know maybe this is an odd quirk of the universe and there’s no good reason for it or maybe when physics takes the next paradigmatic leap, our inability to measure the one-way speed of light will be the obvious the clue to the way General Relativity, Quantum Mechanics, space and time are all connected. And we’ll wonder why we didn’t see it before.
I hope I got your attention with this piece. This is a theory can not be debunked as there is no valid fact to neither help it or to disapprove it. If you liked this writing, you can check out some of my favorites..
Kardashev’s Civilization Scale Analysis: The Type of Civilization We Really Are
This Is About The Extraordinary Journey of One of The Greatest Human Creations- The Voyager
or just check out my profile here for more.
