A Slower Speed of Light (2012) | Hacker News Reader

A Slower Speed of Light (2012)

gamelab.mit.edu

223 pointsgurjeet61 comments

https://web.archive.org/web/20240513041141/http://gamelab.mi...

For a good introduction to developing an intuition about special relativity via low speed of light, I really recommend George Gamow’s “Mr Tompkins in Wonderland” (or “in paperback”). These short stories explore things like how the world would look if the speed of light were 10 mph.

Wow thank you I cant believe I've been ignorant of this my whole life. Thank you so much

https://en.m.wikipedia.org/wiki/Mr_Tompkins

    > Four Books in the Series
    > 
    1940: Mr Tompkins in Wonderland  
    1945: Mr Tompkins Explores the Atom
    1953: Mr Tompkins Learns the Facts of Life
    1967: Mr Tompkins Inside Himself

There's a joke there in those last two titles but I'm not going to make it.

Also from Gamow, and something that blew my (then) 12 year old mind: 1-2-3-Infinity

https://en.m.wikipedia.org/wiki/One_Two_Three..._Infinity

But does that make any physical sense? All the other speeds we are familiar with would be proportionally slower, since they are all ultimately determined by fractions of the speed of light, right? For example, if the speed of light were 10mph, the speed of sound would be something like 0.6in/h, days would be much, much longer, chemical reactions would take hours etc. Overall, I don't think it would really make any difference for a human in this world: everything would actually be perfectly identical.

Why would these dependent on the speed of light?

Because the basic understanding of physics is that all particles move at constant speed c in spacetime; the proportion of their speed that is happening in the three spatial dimensions is determined by their mass. So, any particle's speed through space is a fraction of the "speed of light" c; the higher its mass, the lower the fraction.

The other items I mentioned are then caused by the speed of these particles. The speed of sound in a medium is determined by how fast particles collide into other particles in the medium. The speed of the earth around its axis (the length of a day) is determined by the speed of the particles making it up in the warped spacetime of the earth's gravitational field. The speed of chemical reactions is also limited by how fast atoms and electrons move and can interact with each other.

The length of a day, at least, is unrelated. There was a big splash in the news not long ago because it was determined that the length of Earth's day was changing and we might need to change it by a second.

Venus has a much, much slower rotation on its axis, but Mars is almost the same.

I doubt it was a big splash of news given that leap seconds have been a fairly routine thing for quite a while. Lately there’s been talk about a possible negative leap second, as Earth’s rotation speed has been increasing for a few years now. Many things can have a measurable on Earth’s rotation, including dynamics of the molten outer core, earthquakes, ocean currents, and melting of polar ice caused by the climate change.

Even before we invented precise enough clocks that there was any need for leap seconds, we knew that Earth’s rotation is slowing down due to tidal drag – the moon is literally robbing angular momentum from Earth, and getting farther from Earth in the process. Back in the Cambrian, day length was around 21 hours. Shortly after the formation of the moon, 4.5Ga ago, it would have been only around five hours, assuming the giant impact hypothesis is correct.

Leap seconds are just an imperfection in how we measure days. The recent splash was largely because it was being blamed on changes due to global warming.

In any case, it all goes to my point- the Earth's mass has no bearing on its rotational speed.

I am not a physicist:

I've read that C is really the speed of causality, and that electromagnetic radiation is really a disturbance in the EM field that is propagating along a path. A photon is really information about a prior event, that caused the disturbance i.e. emitted the photon, propagating across the EM field at the rate C. Likewise gravity, the strong force, and the weak force are also propagated at the speed of causality. E.g. if the Sun suddenly doubled in mass for some reason, it wouldn't just take eight minutes for us to see the change in EM radiation, it would also take eight minutes for us to feel the gravitational change.

The whole bit about the physical laws being the same follows from that, and the assumption that there isn't any way to transmit forces across spacetime except through transmission of causality.

I don't know whether it makes physical sense. There are other fundamental constants, too. Changing just "c" might lead to stuff like "atoms can't exist" or "the universe as we understand it would not evolve," etc. Or, not.

Changing "c" is different from just changing your units.

Yes, changing c would definitely lead to stuff like "reality does not exist as we know it".

c goes into many other constants and determines most of the laws, especially in e&m. Realistically, atoms would not be able to hold up against the pressure to collapse, pretty much all matter (if it still existed) would condense to very very very cold solids instantly. We'd be shut out of most light from the sun for potentially hundreds of thousands of years.

I'm just starting my big graduate theoretical physics journey so i really can't do all the relativistic quantum math yet, take what i say with a grain of salt!

AAUI the basic laws can be expressed with dimensionless constants, and in modern physics c is a conversion factor for convenience. I don't know if there's a way to adjust all of the "real" physical constants conjointly which would amount to "just like the Standard Model with a different c".

I want to say it's not incoherent to say e.g. "Newtonian mechanics, but relativistic, with a different c", except of course e.g. Newtonian gravity with its action at a distance doesn't fit, and I wonder if really even contact forces fully work if you try to follow through every detail.

I think the actual answer to your question is that the outcome you're hypothesizing would be absolutely useless for teaching the reader about relativistic effects, so there's no reason for someone to write such a book for a lay audience.

Also see Redshift Rendezvous by John E. Stith. It's a novel, not a tutorial, but relativistic effects play a major part at several points.

Related game

Velocity Raptor (2012): https://www.testtubegames.com/velocityraptor.html

Previously discussed:

- "Velocity Raptor – an adventure in 2+1 dimensions" (Mar 2015, 39 comments): https://news.ycombinator.com/item?id=9247460

I am pleasantly surprised to see this still online (ported from Flash to HTML5).

There was once a flash game that integrated principles of relativity into its mechanics for teaching purposes. It was a series of 2D rooms with the goal being to move from point A to B. I remember there being changing distances as well as colors, for example moving a certain way would change the color of a lock so that the key of that color could unlock it. It was good fun, and it was written by a physicist and hosted on a humble personal site. I can't remember where I saw it, but if anyone knows the reference, please share a link.

Was it Velocity Raptor? https://news.ycombinator.com/item?id=40342086

Yes! Thank you! It's a wonderful game!

Cool concept, but this game made me start to feel sick by the 5 minute mark when I finished it.

The next version could be what happens as alpha approaches exactly 1/137.

My understanding (as a layperson) is that if the fine structure constant changes even a little bit, you basically don’t have atoms or molecules as we understand them. So the game would be something like:

a=1/1: Nothingness as far as the eye can see

…

a=1/136: Nothingness as far as the eye can see

a=1/137: BOOM! Life, the universe and everything

Maybe I’m off, and maybe I have the numbers backwards (again, I’m a layperson), but I feel like the speed of light may be an unusual case among universal constants in that you can actually show an interesting gradient of effects as it changes.

That is not how I remember physics (former PhD student here): The speed of light has a dimension, so it in itself does not change physics (thought experiment: everybody switches to feet-per-decade as the unit of choice, nothing really changes). It is the dimensionless constants that determine the real physics.

Have not heard the statement that is alpha was a tiny factor larger/smaller that would make atoms no longer exist. It's this were true, this would actually be a way to actually calculate it from first principles ('at which value of alpha are there solutions to this equation'). Edit: typo

Your memory is playing tricks on you.

The speed of light does change physics, as does any fundamental constant. Expressing a speed in different units does indeed yield different numbers, but that is not equivalent to a change of speed.

Changing alpha means that electromagnetic force get stronger or weaker, thus the atoms still exist but with different orbital levels. Considering how intricate the orbital levels of atoms are, it's not shocking that a tiny change in alpha completely redefines chemistry, but chemistry would still exist.

The point is that all of the speeds we measure are actually measured in units of the speed of light, if you go right down to it (seconds and meters are defined in terms of the speed of light). So, the value of the speed of light doesn't really matter - which is why c=1 is often used in many kinds of physics.

When people talk about changing the speed of light, they’re obviously not talking about that sort of bookkeeping.

The fine structure constant is dimensionless and would be different if c were different. When doing a unit conversion, one also has to alter other constants so as to be consistent with observed reality; whether one alters other constants or not is the difference between talking about a change in units and a change in c.

From Wikipedia https://en.wikipedia.org/wiki/Fine-structure_constant and following further links:

  4*π*ε_0*ħ*c*α = e^2

e is the charge, h is the Planck constant, ε_0 is the electric constant

However, h is heavily related to c with

  E (photon energy) = h*c/λ

where λ is wavelength. And,

  ε_0 = 1 / (μ_0*c^2)

where μ_0 is the magnetic constant, and is determined experimentally as 4π × 1.00000000055(15)×10−7 H⋅m−1.

A Kibble balance (dog food?) has become an instrument for measuring weight from a known current, rather than measuring current from a known weight.*

It looks like this still doesn't cancel out? It's an interesting point as to whether our hypothetical change in c would affect the relationship between photon energy and wavelength, but either way we get a nonzero power of c.

There is the Hoyle state, a peculiar resonance state that is very important for nucleosynthesis. Without it, stars would not produce a lot of carbon. It appears to be finely tuned for complex chemistry and thus life to evolve.

Wikipedia says the the strong force must be within 0.5% of some value and the finestructure constant within 4%: https://en.wikipedia.org/wiki/Fine-tuned_universe#Carbon_and...

Not an expert here, what is alpha ?

It might be a more fundamental constant than the speed of light as it relates the properties of space time and energy.

At some point if you change the speed of light the information exchange inside of atoms would be disrupted and the system collapses.

Another game in this vein of "teaching math/physics through gameplay" is Hyperbolica, where you explore a 3D world with hyperbolic (and later spherical) geometry. It's mind bending.

https://store.steampowered.com/app/1256230/Hyperbolica/

Oh wow! I remember this thing from forever ago!

Very cool concept

This thing was a monster to try to run on computers of the day when it came out.

Heh - 'core 2 duo' .. that's about 2005 vintage isn't it? Should be nice and smooth on modern hardware.

What would happen if say you were traveling 1 m/s and the speed of light was 2m/s?

I imagine there has to be some special properties when youre at exactly half, or some other special ratio of the speed of light

I know I've seen YouTube videos about that

maybe this one?

https://youtu.be/ge_j31Yx_yk

Not really AFAIK, since it's an asymptote regarding your speed vs speed of light, so it's a pretty continuous curve. The point where things become weird is at close to the speed of light so in your example at like 1.9~1.999 m/s, and physics "break" at 2m/s, but there's not a sigle point between 0~1.999 where anything "surprising" happens.

I feel like your field of vision expanding and everything around you freezing might be considered surprising. These don't become noticeable until near the top end.

Yes but I purposefully used "a single point" in my phrase; since this phenomena doesn't happen in discrete steps, but in a continuum.

Things get "weird" non uniformly at all the various fuzzy intervals where the effects of relativity are significant in scale compared to the measurement error, in time and space dimension, of whatever phenomena you are studying or experiencing. There are many of these phenomena at different scales, and which ones you care about is subjective.

Could we create a vacuum tube and accelerate macroscopic objects in this tube close to the speed of light?

Note how big large particle accelerators are, such as the LHC, and that only gets a proton up to 99.9999991% c.

Our best effort so far: https://en.wikipedia.org/wiki/Large_Hadron_Collider

Ratios only matter in vibrations (frequencies) because the vibration is a non-uniformity within a period. Translational speed isn't like that.

The main point of special relativity (Lorenz transform) is that it is a mapping between [0, c] and [0, infinity], so ratios to speed of light are not absolutely definable. Light has infinite speed in its own reference frame.

> Light has infinite speed in its own reference frame

This also means that from the perspective of photon, everything happens instantaneously.

"You took 5 billion years to get here, dinner is cold"

"But I swear I just left!"

> Light has infinite speed in its own reference frame.

Or alternatively, light doesn't have a reference frame.

I've been curious what a version of this based on general relativity would be like and whether that would be interesting.

Playing this game on my 27” iMac was the first time I experienced nausea from motion sickness. I felt ill for two days.

Player beware!

Sir, we have reached alpha centurion, please use the puke bag.

Funny that it doesn't use the MIT license

Its underlying library, OpenRelativity, does.

Native port for Linux :)

Tested to work on a core2duo cpu…

Oh wait... 2012...

Note it comes as a .tgz but is really only a tar file, not gzipped

(2012)

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