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originally posted by: zundier
Have you ever measured the Speed of Light? If so, did you measure again?
Forgive me for bad english. Of course we're certain about lot's of things in life. I'm just curious of your opinion as a professional scientist regarding the possibility of an ultimate truth? Surely we're are Zillions from it, from Science. But is it achievable?
Just like to add: I'm no one, not scientist, not even close. Just curious and love science. I don't mean to be aggressive, sorry if english writing may look like it.
Your whole answer is good. Regarding that list of speed of light measurements, there's an unsolved mystery in an experiment not listed.
originally posted by: ErosA433
From here you can see a few measurements that have been made.
We don't know if the universe has an edge or not, it may not. Even if it does have an edge it is almost certainly not expanding at near c. The edge of the observable universe is expanding at about 3 times c, and if there's an edge to the universe it's got to be beyond the observable universe and therefore likely to be expanding at not less than 3c. Think about how the edge of the observable universe could be 46.5 billion light years away. If it was only receding at c and the universe is only 13.8 billion years old, how could it be more than 13.8 billion light years away?
originally posted by: StanFL
a reply to: Arbitrageur
The edge of the universe is expanding at near c, so you would need inordinate amounts of energy to get there, but once there you could sail on out to Universe-2 just by waiting, assuming you aimed correctly.
He can discuss exotic matter (and its applications), but making it is another story. I'll have to see it to believe it.
The methods of producing effective exotic matter (EM) for a traversable wormhole (TW) are discussed. Also, the approaches of less necessity of TWs to EM are considered. The result is, TW and similar structures; i.e., warp drive (WD) and Krasnikov tube are not just theoretical subjects for teaching general relativity (GR) or objects only an advanced civilization would be able to manufacture anymore, but a quite reachable challenge for current technology
originally posted by: Arbitrageur
The edge of the observable universe is expanding at about 3 times c, and if there's an edge to the universe it's got to be beyond the observable universe and therefore likely to be expanding at not less than 3c. Think about how the edge of the observable universe could be 46.5 billion light years away. If it was only receding at c and the universe is only 13.8 billion years old, how could it be more than 13.8 billion light years away?
It sounds like you meant to reply to me instead of Stan. Putting the best vacuum in a pipe he could was the best Michelson could do in 1930, because there was no "vacuum of space" available then. The space age didn't even begin until 1957.
originally posted by: Cauliflower
a reply to: StanFL
Why didn't Michelson choose a metric pipe length for the interferometer, or better than that the vacuum of space?
They had been working on the meter standard pre US civil war.
I think you are missing something. Nothing travels faster than c locally, but what we actually measure in terrestrial labs is cosmological redshift and we now know to a confidence level of 23 sigma that it's not Doppler shift as was thought when the redshifts were first discovered.
originally posted by: delbertlarson
So the claims made above must rely on some theorizing that we can't actually test in our terrestrial labs - which for me puts this more in the realm of speculation than science. I am missing something?
We use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the Universe. To show the abundance of these misconceptions we cite numerous misleading, or easily misinterpreted, statements in the literature. In the context of the new standard Lambda-CDM cosmology we point out confusions regarding the particle horizon, the event horizon, the ``observable universe'' and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests. Attempts to restrict recession velocities to less than the speed of light require a special relativistic interpretation of cosmological redshifts. We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23 sigma.
originally posted by: ErosA433
Typically a measurement made by a lab will do well to get within a few % of the accepted value, going for specialist equipment/methods you might get a few 10ths maybe 100ths of % but two measurements are unlikely to be identical, like, ever. This is the experimental method. You will always get statistical and systematic uncertainties.
The results were not as satisfactory as the San Antonio experiments. Much of it was due to the vacuum, or lack thereof. Michelson originally thought a vacuum of 2″ (50 mm of Mercury) would be adequate for good seeing. However it was found that to get sharp images in the tube, vacuum levels had to be brought down to 1 to 2 mm of Mercury. Given the many pipe joints, method of sealing and power of the pumps, this was almost impossible to achieve.
Beyond the vacuum, there were other problems. Heating of the residual air in the beam by the Sun caused the image to vanish, thus most measurements had to be taken after dark. Best measuring seemed to be when the tube was enveloped in the seasonal thick fog that occurs in the area. And there were strange, unexplained cyclic drifts in the measurements. It was thought for a while it could be a tidal influence, but correlation was weak. Some of it was put down to the clay like soil the tube was anchored to, which shifted due to changes in moisture content. The tube was also placed parallel to a drainage ditch, in which varying flows of water occurred.
Again I think you're missing something, because that quote from Eros doesn't imply that 23 sigma can't be achieved with a not so good measurement system if your measurements are far enough off from the hypothesized values.
originally posted by: delbertlarson
But 23 sigma? C'mon man!
I know the contexts are different. But the point is still - how can you measure anything to 23 sigma?
Granted there are assumptions, and sometimes they turn out to be wrong or not quite right. The "standard candles" astronomers use turned out to not be quite as standard as they thought, so the assumption they were standard was somewhat flawed (though not by a lot). However with further research astronomers determined that by watching how quickly the Type Ia light curve decays in the 15 days after maximum light in the B band, they could account for small differences in luminosity due to mass difference that were previously not considered. It gets quite detailed and complicated so generic hand-waving arguments are not very persuasive though if you have genuine concerns about specifics in the approaches used by astronomers and can point out something they've overlooked that might be helpful, but it seems to me they are looking at things quite carefully, which is how they discovered their "standard candles" weren't completely standard.
And then we have the issue that the light itself travels billions of light years through space, and over billions of years in time, to get to us. What do we assume about how it got here? It just seems like there's a lot of assuming going on to claim 23 sigma.
Originally thought to be standard candles where every SNIa had the same peak brightness, it has been shown that this is close to the truth, but not quite. SNIa exhibit brightnesses at maximum that range from about +1.5 to -1.5 magnitudes around a typical SNIa. It has also been shown that the over or under luminosity of these objects is correlated to how quickly the Type Ia light curve decays in the 15 days after maximum light in the B band. This is known as the luminosity – decline rate relation and is the underlying concept which turns SNIa into one of the best distance indicators available to astronomers.