# Knock-on physics effects of a change in the speed of light?
**URL:** https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738
**Category:** Factual Questions
**Created:** [January 1, 2020, 7:46pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738 "2020-01-01T19:46:24Z")
**Posts on this page:** 17
**Page:** 1
### Author:  [@brossa](https://boards.straightdope.com/u/brossa)
#### Post date: [January 1, 2020, 7:46pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/1 "2020-01-01T19:46:24Z")
So God’s lab coat sleeve snags on a rheostat sitting on the benchtop where he’s running the UniverseAsWeKnowIt, and the speed of light is doubled. I assume we would all drop dead, but what does God observe? The speed of light turns up in a lot of places, so how does reality warp to accommodate the change?. What other ‘constants’ and processes are affected? Give me the highlights. If it’s cooler, you can assume that the speed of light has halved.
I would guess that if c doubles, the vacuum permittivity falls, the force felt between charged particles rises, atoms get bigger, fusion in suns slow down, matter becomes less dense, orbits become unstable, that sort of thing.
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### Author:  [@Keeve](https://boards.straightdope.com/u/Keeve)
#### Post date: [January 2, 2020, 3:57pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/2 "2020-01-02T15:57:19Z")
You should check out _Fantastic Voyage II: Destination Brain_ by Isaac Asimov. He was very upset by the scientific inaccuracies that were in the original movie and novelization, so he wrote this NOT as a sequel, but as a rewrite that would be a less-horrible violation of physics. In this version, the scientists in this version accomplished miniaturization by changing Planck’s Constant, and the novel explains the effects that would result from such a change.
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### Author:  [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)
#### Post date: [January 2, 2020, 4:20pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/3 "2020-01-02T16:20:47Z")
The stars would suddenly become a lot bigger/hotter/brighter due to E = mc2 yielding 4x as much energy as it used to.
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### Author:  [@Riemann](https://boards.straightdope.com/u/Riemann)
#### Post date: [January 2, 2020, 4:39pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/4 "2020-01-02T16:39:44Z")
> [@brossa](#):
>
> I would guess that if c doubles, the vacuum permittivity falls, the force felt between charged particles rises, atoms get bigger, fusion in suns slow down, matter becomes less dense, orbits become unstable, that sort of thing.
Well, here you’re getting closer to what’s important. The speed of light “changing” doesn’t really mean anything, since it’s described in arbitrary units. It’s somewhat analogous to asking - what if all the lengths in the universe doubled? Well, how would we know, since all the rulers would be twice as long, too?
Recent thread talking about this.
[http://boards.straightdope.com/sdmb/showthread.php?t=884052](http://boards.straightdope.com/sdmb/showthread.php?t=884052)
The constants that determine the properties of the universe are all dimensionless.
> **[Dimensionless physical constant](https://en.wikipedia.org/wiki/Dimensionless_physical_constant)**
>
> In physics, a dimensionless physical constant is a physical constant that is dimensionless, i.e. a pure number having no units attached and having a numerical value that is independent of whatever system of units may be used.
> The concept should not be confused with dimensionless numbers, that are not universally constant, and remain constant only for a particular phenomenon. In aerodynamics for example, if one considers one particular airfoil, the Reynolds number value of the laminar–turbulent t...
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### Author:  [@TriPolar](https://boards.straightdope.com/u/TriPolar)
#### Post date: [January 2, 2020, 4:46pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/5 "2020-01-02T16:46:02Z")
Doesn’t changing the MPH measurement of the speed of light just change the measurement of a mile or an hour? This is not a stupid question meant to resemble humor, we went over this in some other thread, the speed of light is a constant, wouldn’t it always be 1 SOL?
I know what the OP means, but does it make any sense?
ETA: Well I guess **Riemann** just answered that.
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### Author:  [@brossa](https://boards.straightdope.com/u/brossa)
#### Post date: [January 2, 2020, 5:08pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/6 "2020-01-02T17:08:18Z")
Thanks, **Riemann** , I hadn’t seen that thread for some reason.
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### Author:  [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)
#### Post date: [January 2, 2020, 5:16pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/7 "2020-01-02T17:16:08Z")
John E. Stith’s _Redshift Rendezvous_ (1990) is a murder mystery set on a spaceship where the speed of light is 10 meters per second. It rigorously works out the relativistic effects because they now affect people on an everyday basis, not just in situations humans never normally encounter. One of the best super-hard science fiction idea novels.
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### Author:  [@brossa](https://boards.straightdope.com/u/brossa)
#### Post date: [January 2, 2020, 5:17pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/8 "2020-01-02T17:17:33Z")
So would the question be answerable in a different way if it was posed as God changing some dimensionless physical constant like the fine structure constant or the mass ratio of electron to proton? Presumably we can conceive of a universe unlike our own in which an electron is 1/50 the mass of a proton instead of 1/4.18546 × 10^23?
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### Author:  [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)
#### Post date: [January 2, 2020, 5:19pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/9 "2020-01-02T17:19:12Z")
> [@Riemann](#):
>
> The speed of light “changing” doesn’t really mean anything, since it’s described in arbitrary units. It’s somewhat analogous to asking - what if all the lengths in the universe doubled? Well, how would we know, since all the rulers would be twice as long, too?
So let’s say c was doubled last night by God, and today it is 599584916 m/s. Are you saying our measurements would still indicate c is 299792458 m/s since the meter and second would both double at the same time? And if _that’s_ true, how do we know c is really fixed? What if it’s changing all the time, but we don’t know it?
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### Author:  [@Buck\_Godot](https://boards.straightdope.com/u/Buck_Godot)
#### Post date: [January 2, 2020, 5:26pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/10 "2020-01-02T17:26:43Z")
> [@Riemann](#):
>
> Well, here you’re getting closer to what’s important. The speed of light “changing” doesn’t really mean anything, since it’s described in arbitrary units. It’s somewhat analogous to asking - what if all the lengths in the universe doubled? Well, how would we know, since all the rulers would be twice as long, too?
I think the problem is that, unless you also change the physical location of all particles in the universe when you change c, all of the rulers wouldn’t be twice as long, at least at first. If the physics definition of length suddenly doubled, then your yardstick would, from a physics point of view, be suddenly compressed to 1.5 feet. At that point the forces involved would probably cause it to explode. This would happen to everything simultaneously. It would not be good. Please don’t do this.
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### Author:  [@Keeve](https://boards.straightdope.com/u/Keeve)
#### Post date: [January 2, 2020, 5:31pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/11 "2020-01-02T17:31:52Z")
> [@Exapno\_Mapcase](#):
>
> John E. Stith’s _Redshift Rendezvous_ (1990) is a murder mystery set on a spaceship where the speed of light is 10 meters per second. It rigorously works out the relativistic effects because they now affect people on an everyday basis, not just in situations humans never normally encounter. One of the best super-hard science fiction idea novels.
Just ordered it from Amazon. Thanks!
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### Author:  [@Ludovic](https://boards.straightdope.com/u/Ludovic)
#### Post date: [January 2, 2020, 5:50pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/12 "2020-01-02T17:50:22Z")
> [@TriPolar](#):
>
> Doesn’t changing the MPH measurement of the speed of light just change the measurement of a mile or an hour? This is not a stupid question meant to resemble humor, we went over this in some other thread, the speed of light is a constant, wouldn’t it always be 1 SOL?
> [@Buck\_Godot](#):
>
> If the physics definition of length suddenly doubled, then your yardstick would, from a physics point of view, be suddenly compressed to 1.5 feet. At that point the forces involved would probably cause it to explode. This would happen to everything simultaneously. It would not be good. Please don’t do this.
So, the speed of light would still be SOL, and so would everything else.
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### Author:  [@Riemann](https://boards.straightdope.com/u/Riemann)
#### Post date: [January 2, 2020, 6:43pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/13 "2020-01-02T18:43:19Z")
nm
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### Author:  [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)
#### Post date: [January 2, 2020, 7:21pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/14 "2020-01-02T19:21:51Z")
> [@Exapno\_Mapcase](#):
>
> John E. Stith’s _Redshift Rendezvous_ (1990) is a murder mystery set on a spaceship where the speed of light is 10 meters per second. It rigorously works out the relativistic effects because they now affect people on an everyday basis, not just in situations humans never normally encounter. One of the best super-hard science fiction idea novels.
For everyday effects of a slower speed of light, check out a game created by folks at MIT called…
[A Slower Speed Of Light.](https://www.youtube.com/watch?v=hyj1ZZiseDE)
Once you get past the depressing premise of the game, it gets interesting. The player moves around a village, collecting tokens that gradually lower the speed of light until it gets pretty close to the speed at which the player is moving around. The game models the relativistic visual effects: redshift/blueshift, the distortion of perceived depth, and so on. Quite interesting.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [January 2, 2020, 9:17pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/15 "2020-01-02T21:17:01Z")
> [@](#):
>
> Quoth **brossa** :
>
> So would the question be answerable in a different way if it was posed as God changing some dimensionless physical constant like the fine structure constant or the mass ratio of electron to proton? Presumably we can conceive of a universe unlike our own in which an electron is 1/50 the mass of a proton instead of 1/4.18546 × 10^23?
That is a sensible question, and in fact there’s been some work which seems to suggest that the Fine Structure Constant has in fact changed over the lifespan of the Universe. One could certainly envision that happening, and (in principle) calculate and predict what the results would be.
Mind you, it would be an incredibly _difficult_ question, but that’s what makes it fun.
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### Author:  [@Senegoid](https://boards.straightdope.com/u/Senegoid)
#### Post date: [January 2, 2020, 9:42pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/16 "2020-01-02T21:42:39Z")
According to some discussions I have read, if some of those underlying constant parameters of the universe were different, even by a little bit, then the whole universe would be a very uninteresting place. I’ve seen this stated in terms something like “Life could not exist in such a universe.” Upon closer reading, what they are really saying is that quarks could not even coalesce to form protons or neutrons, so no matter at all would exist.
I imagine a universe consisting entirely of complex probability wave functions, never coalescing to form so much as a particle. What a waste of a universe.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [January 2, 2020, 10:34pm UTC](https://boards.straightdope.com/t/knock-on-physics-effects-of-a-change-in-the-speed-of-light/845738/17 "2020-01-02T22:34:36Z")
You start getting into the Puddle Argument, though. Sure, Life as We Know It depends on quarks and so on, but who’s to say there might not be something else life-ish (or intelligent, or whatever other criterion you’re using for “interesting”) in one of those other universes?