The Science Thread

Light-hearted discussions, forum games and anything that doesn't fit into the other forums.
Tech Corner - Firewalls, AV etc. - Report Bugs - Board Rules
User avatar
Gaidal Cain
Round Table Hero
Round Table Hero
Posts: 6972
Joined: 26 Nov 2005
Location: Solna

Unread postby Gaidal Cain » 06 Nov 2009, 06:25

Kristo wrote:Yes, and we've defined time in terms of the decay rate of a cesium atom. Do we really know enough about the effects of gravity and high angular velocity on cesium atoms to be sure we're really observing time dilation?
Well, there could of course be some other weird effect that gives the same result as relativity, but considering that there are other ways of checking if it is correct or not, it seems very, very unlikely.
You don't want to make enemies in Nuclear Engineering. -- T. Pratchett

User avatar
Banedon
Round Table Knight
Round Table Knight
Posts: 1825
Joined: 06 Jan 2006

Unread postby Banedon » 06 Nov 2009, 09:27

Kristo wrote:Can we even set up an experiment to test whether the speed of light is still c when moving sufficiently fast? I don't know if we can move something fast enough where you couldn't explain away any differences to experimental errors. We're fixed relative to the Earth, but the Earth is moving at 20-30 km/sec around the sun, the sun is moving at 200 km/sec through the galaxy, and the galaxy is moving at who knows how fast across the universe. And I'll bet even that last number isn't large enough relative to c to matter.

I'm comfortable with the laws of physics being the same in all reference frames. I can't wrap my head around "Speed of light = c" being one of those laws. To my Newtonian mind, light is always in the absolute reference frame. I can't comprehend a reason why you can't move relative to it.
I'm positive, but not certain, that we can test that the speed of light is a constant up to the limitation Gaidal Cain wrote about. That's because atomic clocks right now are fantastically precise (many many many orders of magnitude can be measured).

By the way if you accept the principle of relativity, and if you accept that the laws of electromagnetism are valid, then you must also accept that the speed of light is invariant no matter what reference frame you're in. "Speed of light = c" isn't a law, it's a consequence of the laws.
Kristo wrote:Yes, and we've defined time in terms of the decay rate of a cesium atom. Do we really know enough about the effects of gravity and high angular velocity on cesium atoms to be sure we're really observing time dilation?
There are linear accelerators around, so no (or not much) angular velocity - see SLAC: http://www6.slac.stanford.edu/AboutSLAC.aspx

Otherwise I'm not sure what you mean ... are you saying that possibly the caesium atoms are moving fast enough / under sufficient gravitational attraction that our understanding of its behaviour fails?
I'm a hypocrite because I suggested that all life is sacred and should not be wasted without good reason.

User avatar
Kristo
Round Table Knight
Round Table Knight
Posts: 1548
Joined: 23 Nov 2005
Location: Chicago, IL

Unread postby Kristo » 06 Nov 2009, 13:58

I'm just saying that maybe being at a 14,000+ km orbit affects cesium's oscillation rate. You've got extreme cold, lower pull from Earth's gravity, and solar radiation to contend with. We're only talking about 38 microseconds per day here. And once again, I can't argue with the fact that the Special and General Relativity equations give what is apparently the right answer (i.e., GPS works quite well).

I'm not comfortable treating modern science like a religion, meaning that I believe it but don't understand it. But that's where I am right now. It's just plain weird.
Peace. Love. Penguin.

User avatar
Gaidal Cain
Round Table Hero
Round Table Hero
Posts: 6972
Joined: 26 Nov 2005
Location: Solna

Unread postby Gaidal Cain » 06 Nov 2009, 17:07

Well, there's a difference in the fact that science gives predictions which you can check; there's not much of that in religion. You could argue over things like string theory, but from what I know of it, it's still more of a mathematical construct than a proper theory.

And I'd like to point out that there's nothing that says that the Maxwell equations can't be somehow flawed; after all, Newtonian mechanics worked really, really well for about 200 years. It's experiment that verify that equations and theory describe reality, not equations that verify that a theory is correct.
You don't want to make enemies in Nuclear Engineering. -- T. Pratchett

User avatar
Corribus
Round Table Knight
Round Table Knight
Posts: 4994
Joined: 06 Jan 2006
Location: The Duchy of Xicmox IV

Unread postby Corribus » 06 Nov 2009, 21:32

By the way, just in case anyone is interested.

I have reinitiated this thead over at HC, focusing on nanotechnology as the thread was originally supposed to. It can be found here.
"What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?" - Richard P. Feynman

User avatar
Banedon
Round Table Knight
Round Table Knight
Posts: 1825
Joined: 06 Jan 2006

Unread postby Banedon » 17 Nov 2009, 07:40

Random question: is this quote from Wikipedia ridiculous or a mistranslation or ... ?
Wikipedia article on Shapiro delay wrote:Quote by Einstein

"In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity ; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light)." - Albert Einstein (The General Theory of Relativity: Chapter 22 - A Few Inferences from the General Principle of Relativity)
No matter how I look at it, the speed of light is a simple constant that's even built right into relativity (u.u = 0, etc). How on EARTH can Einstein possibly say it isn't??
I'm a hypocrite because I suggested that all life is sacred and should not be wasted without good reason.

User avatar
ThunderTitan
Perpetual Poster
Perpetual Poster
Posts: 23270
Joined: 06 Jan 2006
Location: Now/here
Contact:

Unread postby ThunderTitan » 17 Nov 2009, 08:42

Because like math it all relies on conventions... using the speed of light as a constant is probably required to express the theory mathematically or something.

Also: http://www.bartleby.com/173/22.html



And some perspective on the matter of science: http://www.newscientist.com/blogs/short ... unive.html

Plus some stuff that's just interesting: http://www.newscientist.com/article/mg1 ... ?full=true
Disclaimer: May contain sarcasm!
I have never faked a sarcasm in my entire life. - ???
"With ABC deleting dynamite gags from cartoons, do you find that your children are using explosives less frequently?" — Mark LoPresti

Alt-0128: €

Image

User avatar
Pol
Admin
Admin
Posts: 10056
Joined: 29 Nov 2005
Location: IN SOMNIS VERITAS
Contact:

Unread postby Pol » 17 Nov 2009, 10:57

ThunderTitan wrote:using the speed of light as a constant is probably required to express the theory mathematically or something.
Of course that is, that's why you need constants. You set them and calculate deeper.

[q="fe:"] ..a number representing a quantity assumed to have a fixed value in a specified mathematical context; "the velocity of light is a constant[/q]
as one of many dictionary definitions. ;)
"We made it!"
The Archives | Collection of H3&WoG files | Older albeit still useful | CH Downloads
PC Specs: A10-7850K, FM2A88X+K, 16GB-1600, SSD-MLC-G3, 1TB-HDD-G3, MAYA44, SP10 500W Be Quiet

User avatar
Kristo
Round Table Knight
Round Table Knight
Posts: 1548
Joined: 23 Nov 2005
Location: Chicago, IL

Unread postby Kristo » 17 Nov 2009, 16:23

Banedon wrote:No matter how I look at it, the speed of light is a simple constant that's even built right into relativity (u.u = 0, etc). How on EARTH can Einstein possibly say it isn't??
But isn't the whole point of GR to describe how the presence of mass distorts spacetime? I thought it wasn't that light bends, but spacetime itself. The speed of light is still c but the path it takes isn't straight anymore.
Peace. Love. Penguin.

User avatar
ThunderTitan
Perpetual Poster
Perpetual Poster
Posts: 23270
Joined: 06 Jan 2006
Location: Now/here
Contact:

Unread postby ThunderTitan » 17 Nov 2009, 21:32

I have no idea, but i recall that mass distorting spacetime was Einstein's hypothesis on what gravity is...
Disclaimer: May contain sarcasm!
I have never faked a sarcasm in my entire life. - ???
"With ABC deleting dynamite gags from cartoons, do you find that your children are using explosives less frequently?" — Mark LoPresti

Alt-0128: €

Image

User avatar
Banedon
Round Table Knight
Round Table Knight
Posts: 1825
Joined: 06 Jan 2006

Unread postby Banedon » 22 Nov 2009, 11:22

Kristo wrote:
Banedon wrote:No matter how I look at it, the speed of light is a simple constant that's even built right into relativity (u.u = 0, etc). How on EARTH can Einstein possibly say it isn't??
But isn't the whole point of GR to describe how the presence of mass distorts spacetime? I thought it wasn't that light bends, but spacetime itself. The speed of light is still c but the path it takes isn't straight anymore.
Yes, but if the speed of light is a constant then that quote by Einstein is clearly ... wrong. 8| 8|
I'm a hypocrite because I suggested that all life is sacred and should not be wasted without good reason.

User avatar
ThunderTitan
Perpetual Poster
Perpetual Poster
Posts: 23270
Joined: 06 Jan 2006
Location: Now/here
Contact:

Unread postby ThunderTitan » 22 Nov 2009, 11:55

Remember how how high-school physics where all about systems that where perfectly enclosed with no loses and stuff like that that never actually happens in real life?
Disclaimer: May contain sarcasm!
I have never faked a sarcasm in my entire life. - ???
"With ABC deleting dynamite gags from cartoons, do you find that your children are using explosives less frequently?" — Mark LoPresti

Alt-0128: €

Image

User avatar
Kalah
Retired Admin
Retired Admin
Posts: 20078
Joined: 24 Nov 2005

Unread postby Kalah » 22 Nov 2009, 12:42

Yes. Our teacher always said stuff like: "We'll just imagine that this minute number is actually 0, because otherwise the maths won't fit." :D

User avatar
ThunderTitan
Perpetual Poster
Perpetual Poster
Posts: 23270
Joined: 06 Jan 2006
Location: Now/here
Contact:

Unread postby ThunderTitan » 22 Nov 2009, 19:03

Yeah, for some reason most people seem to forget that... annoys the hell out of me.
Disclaimer: May contain sarcasm!
I have never faked a sarcasm in my entire life. - ???
"With ABC deleting dynamite gags from cartoons, do you find that your children are using explosives less frequently?" — Mark LoPresti

Alt-0128: €

Image


Return to “Campfire”

Who is online

Users browsing this forum: Bing [Bot], Google [Bot] and 35 guests