What if the speed of Light were reduced?

90 Night Elf Druid
1.) What if the speed of light suddenly changed to 24,901.55 miles per second (the exact circumference of the earth)? Would we really notice that much difference? If so, what would be the advantages / disadvantages of such a change?

2.) Let's go to the extreme...what if it were suddenly, universe wide, reduced to 100 miles per hour (yes hour not second).?

I know they're silly questions, but I've always just sort of wondered about those and I don't have a physics professor on my friends' list. ;)

Thanks in advance.
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90 Goblin Warrior
I don't remember where but I've seen a show where people were slowing down light and even making it stop moving.
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90 Undead Priest
I'm not a physicist so I can't really answer, but you might find this article interesting. Basically, the speed of light is only a constant in a vacuum like space and scientists have managed to slow bits of light down.

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90 Tauren Shaman
Yes. You can slow light way down, even "stop" or trap it for short periods of time.
But, op, if you are referring to actually lowering the value of c?
Meaning, what would happen to the universe if c gets lowered?

Well, it would effect most (if not all) the other physical constants, which would in turn affect many results we see.

However, from a math point of view, physicists do this all the time when working with equations. They set c = 1, and also h_bar (Plank's constant). But they convert it back in the end to find the answer in the "correct units."

Then again a lot of that stuff (the physical constants) is more definitions as far as units go, but the phenomena would adjust itself to what ever the value of c is.

Now, to us, this would mean that information could not travel as fast as it currently does, that we would not be able to see out as far as we can into the universe, and that the allowed phenomena would change (like what electromagnetic wave modes can travel through a medium or waveguide).
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85 Dwarf Hunter
thats a curious thought.. the second part would have sound moving faster than light.
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90 Tauren Shaman
07/05/2012 07:07 PMPosted by Kendamd
thats a curious thought.. the second part would have sound moving faster than light.

Well, no. That is because sound is based on the interactions of molecules colliding, which could not move faster than light (and don't in materials anyway from our current real world understanding as we have it right now). Special Relativity postulates that nothing will travel faster than light in that reference frame (or material), so, assuming this still holds true when we slow light down, we still have that sound cannot travel faster than light.

Also, information itself is assumed to not be able to move faster than c (which is why tunneling and entanglement are philosophically weird and interesting phenomena), otherwise causality can be messed with.

Also, we can look at phonons. Phonons are the way physicists think about how vibration moves through materials, and are not considered to exceed c (since there is such a thing as optical phonons, or photons acting as phonons).
Edited by Nachtstier on 7/6/2012 9:13 AM PDT
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90 Night Elf Druid
Thanks Nach...cool and interesting reply :)
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85 Tauren Paladin
I'm no professional, but I'll say what I've learned from school/internet/everyday life. Normally, light travels at "ultimate speed", essentially the fastest we can possibly reach. Light can be slowed down, but not sped up past said speed. Einstein said E=mc2 meaning that to reach light speed (c) an object must have infinite energy (no such thing) also as an object accelerates it gains mass until at c it becomes infinite in mass(probably a bad thing). Other physicists have theorized that we will never be able to reach said speed, but we can get close. And if that were too happen, couldn't you just run in the time machine to add to your current speed? No, Stephen Hawking theorized if we were to get that close to light speed, time inside the time machine would slow down just enough so that would never happen. Essentially, 100 years irl would go by in about 5 years inside the time machine. Meaning theoretically time travel is possible. And actually, objects at rest are traveling through TIME at light speed, so we already are. But what if we were to find a way to travel the speed of light, would we actually be traveling at double the speed? Mind. Blown.
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90 Human Mage
The truth of the matter is a bit more complicated. The speed of light is not technically "ultimate speed". It's more of an unattainable speed. The laws of Relativity say that nothing can reach the speed of light, but there is nothing in them saying that things can't travel faster than light (hence the concept of the tachyon, a theoretical particle that travels faster than light and will, in fact, travel even faster if you take energy away from it). The trick is actually getting from the one state to the other. And physicists have figured out a few cheats to do so, even if they are prohibitively expensive and/or dangerous (such as diving into a spinning black hole, passing through the vortex in its centre, and coming out the other side).

Also, it wasn't Hawking who made that observation. It was one of the necessary assumptions of Relativity by Einstein. The increase in mass, the time dilation, and the length contraction that wasn't mentioned by you are all related to the accelerated object are caused by the exact same effect. By accelerating, the object is being rotated through space-time so that part of its length in the direction of travel actually enters the time dimension, as observed by us, while part of its time dimension is rotated into space, meaning that you can actually see multiple moments of its existence "simultaneously" (as far as simultaneity exists in a relativistic universe). What this means is that you are always moving at the same rate through space-time. At rest, that movement is parallel to the time dimension. When you're travelling, that movement is partially in the time dimension and partially in space. And, the faster you travel, the greater the angle from the time axis you achieve. Light speed is 45 degrees from that axis.

And, to get back to the original discussion from last month, there is actually a story from the first half of the 20th century (sadly, I don't remember what it's called) which addresses that question. In it, the main character is transported into a world where the speed of light is 30 mph. In this world, traffic cops have absolutely nothing to do, since nobody can go past the speed limit. When he decides to ride a bike, he suddenly sees the world distort around him because of length contraction. He stops and finds that a lot more time has passed than what he imagined.

And, if you want to see a more visual representation of it, it might be a good idea to check out Carl Sagan's old documentary, Cosmos, one episode of which visits that universe in order to tell the tale of a boy who takes a ride on his bike while telling his little brother to wait for him. The conclusion in that one is just heartbreaking.
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