You can envision any universe you want, but it would be pretty tough to do this honestly... You'd have to break almost everything familiar.
You can rule out universes with light having a propagation speed greater than information for obvious reasons but, for less obvious reasons, you can also mostly rule out a universe with the same physics as ours but a lower light propagation speed. The only way to make that second part not true that I can think of is to give photons a very small but non-zero rest mass. Otherwise, it's hard to reason about it at all.
To proceed, I'd then assume there's still lorentz invariance but with the information speed rather than light speed. Additionally, they'd have to be pretty close in value to produce what we see.
The big sticking point I have though, is what on earth the electromagnetic force would look like in that scenario. I've no idea.
The assumption that the photon has 0 mass is still being tested, so it's not absurd to imagine it, and the universe may not look really differently if it was non-0 but small enough.
According to [0], the most accepted upper limit on a possible mass of a photon is m < 10^-14 eV/(c^2).
First, attempt to imagine information in a complete void. No space, no energy. On what is that information coded?
You have to pick something. Now, it doesn't have to be self-propagating packets of electromagnetic waves, but whatever you pick will be that universe's equivalent of light.
We can be imaginative and declare that the whole universe has "states", and those states are different. The whole universe encodes states - without anything in the universe required to exist. For example, "laws" of universe depend on states.
The universal limit that results from relativity (c) is the speed of massless particles. The photon is believed to be massless; if it is, its speed must be exactly c. All experiments do far have shown the photon to have 0 mass. However, if it turned out it had some very small but non-0 mass, that wouldn't directly contradict any fundamental theory (though it may have more complex indirect implications on the Standard Model etc).
Depending on what you mean by "the speed of light", it's quite easy.
The speed of light in water is 0.75c, but other things sometimes travel faster than that in water -- Cherenkov radiation (the blue glue in reactors) happens when you have eg electrons moving through the water at speeds faster than 0.75c.
If something was faster than photons and could carry similar information, we'd probably evolve to see those instead of photons. So it seems more like a semantic question.
On the other hand things get really weird if we say the fastest way to transmit information has speed in some way a function of that information (e.g. frequency). https://www.gregegan.net/ORTHOGONAL/00/PM.html
The time it takes light to propagate is not a determining factor in whether or not a particular animal reproduces (namely whether or not it survives to reproduce), so what evolutionary advantage could "faster light" confer?
In a more general sense, just because something exists doesn't mean we would evolve the ability to capitalize on it. Think of all of the abilities that would obviously be pretty advantageous which have evolved in species other than ours--that we didn't evolve a hyper-sensitive sense of smell is clearly not because of some deficiency in the universe because dogs and bears and others managed to evolve it..
The latency caused by the speed of light around us is so tiny as to be irrelevant.
Our reaction times are far greater than the time it takes the light to get to us from anything that could affect us quickly (anything we can eat or that could eat us).
If there were another similar-but-faster thing out there, even if it were thousands/millions/infinity of times faster it would give no real advantage. This feels like basically Amdahl's Law applied to fight-or-flight timing.
Human reaction time is ~0.25 seconds. Light from even 100 meters away takes 300 nanoseconds to get to you. Those are ~6 orders of magnitude off.
If light were millions of times slower, this would stop being true (but then physics wouldn't work anything like the same either, so the point is a bit moot).
Which gives me another opportunity to hype “Dragon’s Egg” a novel by Robert Forward.
From the synopsis in Wikipedia: “Dragon's Egg is a 1980 hard science fiction novel by Robert L. Forward. In the story, Dragon's Egg is a neutron star with a surface gravity 67 billion times that of Earth, and inhabited by cheela, intelligent creatures the size of a sesame seed who live, think and develop a million times faster than humans.”
It takes light 33ns to travel from a cheetah to a gazelle 10 meters away. The time it takes the gazelle to process and react to that information takes many orders of magnitude longer, so optimizing or even eliminating that 33ns isn’t going to affect the gazelle’s chances of survival.
> edit: lol ok HN hates thought experiments, got it.
> fuckin nerds
I don't know man, you proposed a thought experiment, we engaged with it. Doesn't sound like HN hates thought experiments, nor that we're particularly nerdier than you (and I've engaged with you enough in the past to know that you're delightfully every bit as nerdy as I am :) ).
> I mean yes in our world, but also no, the bottleneck if the universe is literally the speed of photons.
Not literally, no. The bottleneck is the speed of things with 0 mass, of which the photon is just one example (as far as we know).
I also think it's very likely that, had there been another force that was ubiquitous but carried by a particle that traveled at 200 km/h, that would be easier to detect than photons or happened to have other favorable properties, we could have easily evolved to detect that instead.
Are these fundamentally related, or could we imagine a universe where these are two different numbers?