Light Speed: Fixed... or Relative? Exploring Einstein's Relativity

GargIndia
I need to give you a two part answer.

Part 1 - Accuracy of measurements
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How do you say a measurement is accurate to a certain degree (or your measurement has a certain precision)?

The answer is - taking the same measurement several times in exactly the same circumstances (external factors) and then finding standard deviation of your measurements. The standard deviation is your precision for that method of measurement.

The problem with time is that you cannot catch time - it elapses. You cannot measure it again.

So when you say that your clock "can keep time to within one second in roughly 3.7 billion years", the question is how did you calculate this.

Part 2 - Is this an "optical" clock?
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From whatever I can understand from the article, the clock is based on atomic vibration (in this case Al ion). How is this an "optical" clock?

Both parts of your reply raise reasonable points. I think one way you can answer both parts and more is by reviewing this paper:

Frequency Comparison of Two High-Accuracy Al+ Optical Clocks

The question about how we know it's accurate to within a second in 3.7 billion years is a reasonable one. Obviously nobody has run tests for 3.7 billion years to determine this, it's just a a scale of analogy to put accuracy in the perspective of common human perceptions since we can perceive seconds and try to conceive of billions of years, but most people don't cope so well with expressions like 1.7E-16 seconds unless they are engineers or scientists.

On the bottom of the last page in the paper, they give the time interval they used for determining statistical uncertainty of 164967 seconds, which is about 45.82 hours, which is obviously much easier to do on human time scales. The frequency is so high on optical clocks that they can get enough cycles in 45 hours to make predictions on much larger time scales, but in truth we don't know what will happen in 3.7 billion years. The point you should understand is you keep the ratio of 1 second over 3.7 billion years, change the denominator from 3.7 billion years to 45.82 hours, and the numerator will be the fraction of a second which keeps the two ratios the same (after converting everything to seconds or some common unit).

The paper has supporting details like a list of the errors considered in Table 1, and it is by determining the sources of error that the accuracy of the clock is determined.

For the relativity experiment, I'd also add that even if you want to argue that their estimate of the errors could be off, this wouldn't explain a repeatable phenomenon where you can compare 2 clocks at slightly different altitudes then reverse their positions, and the effect is reversed. This is clearly some effect being measured which is independent from the accuracy of the clocks and would still be hard to explain even if you argue the real accuracy may only be 2 seconds in 3.7 billion years instead of 1 second. I don't think you can explain those on the basis of the clocks being inaccurate, because you'd have to explain why the inaccuracy always manifested itself such that the more elevated clock always ran faster, even when you reverse the two clocks.

The beginning of the paper answers part 2 of your question better than I could, so I suggest you read that. As Phage said the frequencies used are much higher than with cesium atomic clocks (over 100,000 times greater), which gives us a lot more cycles to work with, thus improving the potential accuracy dramatically.

dragonridr
Well as usual im going to muddy the waters actually light can travel faster weve done it has to do with its wave function. Here ill let you read the article.

abcnews.go.com...

This is a topic where I do NOT trust science writers based on past experience. I trust the scientists themselves more, and tried to search for the actual paper on arXiv but I haven't found it yet.

Wikipedia has a nice writeup on all the known things that can travel faster than light and I understand most of them, but I don't understand what's in that link you posted, yet. Here's the wiki writeup on the topic, which covers the laser pointer, etc (see section 1.2 Light spots and shadows):

Faster-than-light

reply to post by GargIndia

You don't need three planets. You just need trigonometry and logic.

www.newscientist.com...

www.physicsforums.com...

physics.stackexchange.com...

reply to post by Arbitrageur


We discussed this in class i figure another likely candidate was quantum tunneling to explain the results of there experiment. Here is an experiment explaind by Raymond Chiao from i believe it was UC berkley. But he got light to move faster as well by using quantum tunneling. In fact he was the first to measure its speed he first got a 50 percent increase in the speed of light then pushed for more. Its getting harder and harder to keep up especially in quantum mechanics its mind boggling at times.

www.dhushara.com...

reply to post by Arbitrageur

This is a topic where I do NOT trust science writers based on past experience. I trust the scientists themselves more, and tried to search for the actual paper on arXiv but I haven't found it yet.

It's the group/phase velocity thing. Science writers have a hard time getting it right.

You can see the difference between group and phase velocity when you drop a pebble into a pond. The pebble creates a ring which moves outwards, slower than the actual ripples which make up the ring. The group velocity is the speed at which the ring expands, whereas the phase velocity is the velocity of the invidual ripples making up the ring.

plus.maths.org...

dragonridr
reply to post by Arbitrageur

 

We discussed this in class i figure another likely candidate was quantum tunneling to explain the results of there experiment.
www.dhushara.com...

If it is a quantum tunneling effect, it's the first time I've seen it described in that manner, but it's not clear to me that's what it is. I'm not sure if I'll understand the actual research paper or not when I find it, but it has to be more informative than that article on abcnews.

Phage
It's the group/phase velocity thing. Science writers have a hard time getting it right.

Those are mentioned in sections 1.7 and 1.8 of the wiki link I posted, and I wouldn't be surprised if it's something like that. But aside from the inference that both those and the NEC experiment are discussed on the same page under different headings, does Helen Joyce actually say that's what it is? I'm not saying it isn't and it very well could be, but if she drew a direct correlation between the two, I missed it. The article at abcnews.go.com... definitely doesn't say anything about phase or group velocity.

I definitely agree that science writers struggle with the phase/group velocity topic as well as other FTL topics, and sometimes post inaccurate or misleading articles (or maybe it's you who was agreeing with me).

I have found an nice animation that explains visually what phase / group velocity is

reply to post by dragonridr


I was disagreeing about the shadow and the laser light on planets scenario. Agreeing that maybe light could be passed through the cesium vapor faster then light in a vacuum.

The beginning of this video offers a reason why your light on planet example is not accurate perhaps, but maybe he is wrong?

If I had a car that was going the speed of light and I turned on the headlights would they do anything???

reply to post by RocksFromSpace

You haven't being paying any attention to the discussion, have you?

reply to post by Phage


Yes I have.. it was a joke post..notice the funny face at the end... but thanks for your reply.

RocksFromSpace
If I had a car that was going the speed of light and I turned on the headlights would they do anything???

Depends on the car many might fall apart at that speed.

reply to post by ImaFungi


I said the same thing the dot moves faster than light but no information is transferred. So he actually contradicts himself slightly but yes the dot moves faster than light. He makes another mistake with his tether as well he argued that the force carrying particles move at the speed of light and if the tether was moving at the speed of light it would break apart. Well thats not true he doesnt understand relativity at all. To the force carrying particles they won't know they're moving at the speed of light and behave normally. According to him a spaceship travelling at the speed of light would just break apart thats not true at all.

ImaFungi
reply to post by dragonridr

 

I was disagreeing about the shadow and the laser light on planets scenario. Agreeing that maybe light could be passed through the cesium vapor faster then light in a vacuum.

The beginning of this video offers a reason why your light on planet example is not accurate perhaps, but maybe he is wrong?

His explanation about the light pointer is accurate except for one small quibble.

"The moon illusion" where the moon appears larger on the horizon is an illusion. The moon is not any larger, and you can't measure any size increase with any instruments.

That video refers to the apparent speed of light of a laser pointer going across the moons' surface as an illusion. Unlike the "moon illusion", you can measure the speed at which the dot moves across the moon's surface, and it really IS moving faster than light, so I can't agree with calling it an illusion, at least not in the same way the "moon illusion" is an illusion. I think the wiki link I posted earlier explains it better without calling it an illusion:

If a laser is swept across a distant object, the spot of laser light can easily be made to move across the object at a speed greater than c. Similarly, a shadow projected onto a distant object can be made to move across the object faster than c. In neither case does the light travel from the source to the object faster than c, nor does any information travel faster than light.

Ok i found the NEC press release on the experiment but still no paper. But ill say CBS just read the labs press release so they got the idea generally i guess.

In the experiment, NEC scientists measured the time taken by a pulse of light to pass through a 6cm-long specially prepared chamber containing cesium gas*2. The 3-microsecond long pulse of light would normally take only 0.2 nanoseconds to pass through the chamber in a vacuum. But when passed through the specially prepared chamber, light emerged 62 nanoseconds earlier than it would have had it passed through the chamber in a vacuum. This unusual phenomenon is the result of "anomalous dispersion", an effect not seen in nature in transparent materials and is created by the non-natural thermal state of the cesium gas used in the chamber.

"Our experiment shows that the generally held misconception that nothing can move faster than the speed of light, is wrong. Einstein's Theory of Relativity still stands, however, because it is still correct to say that information cannot be transmitted faster than the vacuum speed of light," said Dr. Lijun Wang. "We will continue to study the nature of light and hopefully it will provide us with a better insight about the natural world and further stimulate new thinking towards peaceful applications that will benefit all humanity."

www.nec.co.jp...

dragonridr
Ok i found the NEC press release on the experiment but still no paper. But ill say CBS just read the labs press release so they got the idea generally i guess.
www.nec.co.jp...

The 3-microsecond long pulse of light would normally take only 0.2 nanoseconds to pass through the chamber in a vacuum. But when passed through the specially prepared chamber, light emerged 62 nanoseconds earlier than it would have had it passed through the chamber in a vacuum.

So, subtract 62 nanoseconds from 0.2 nanoseconds and you get...wait, what? Does that even make any sense?

For example, if it said: "light emerged 0.1 nanoseconds earlier than it would have had it passed through the chamber in a vacuum", then we can calculate it was traveling at 200% the speed of light, which would at least make some sense, sort of. But trying to do the same calculation with the numbers cited yields a negative time interval, something like backwards time travel. Either there's a typo or I'm missing something.

Arbitrageur

dragonridr
Ok i found the NEC press release on the experiment but still no paper. But ill say CBS just read the labs press release so they got the idea generally i guess.
www.nec.co.jp...

The 3-microsecond long pulse of light would normally take only 0.2 nanoseconds to pass through the chamber in a vacuum. But when passed through the specially prepared chamber, light emerged 62 nanoseconds earlier than it would have had it passed through the chamber in a vacuum.

So, subtract 62 nanoseconds from 0.2 nanoseconds and you get...wait, what? Does that even make any sense?

For example, if it said: "light emerged 0.1 nanoseconds earlier than it would have had it passed through the chamber in a vacuum", then we can calculate it was traveling at 200% the speed of light, which would at least make some sense, sort of. But trying to do the same calculation with the numbers cited yields a negative time interval, something like backwards time travel. Either there's a typo or I'm missing something.

Thats funny same things my students did thats why we started speculating on time travel like i said earlier. Id really love to see that paper.This was sent to me in an attempt to show Einstein was wrong you know everyone when they first tackle physics question relativity.And we correct them by describing information transfer. Thank god i only have to do class once a week id much rather stay in research.

dragonridr
reply to post by ImaFungi

 

I said the same thing the dot moves faster than light but no information is transferred. So he actually contradicts himself slightly but yes the dot moves faster than light. He makes another mistake with his tether as well he argued that the force carrying particles move at the speed of light and if the tether was moving at the speed of light it would break apart. Well thats not true he doesnt understand relativity at all. To the force carrying particles they won't know they're moving at the speed of light and behave normally. According to him a spaceship travelling at the speed of light would just break apart thats not true at all.

No the 'dot' would not be moving faster then light, because there is no dot! this 'dot' you are referring to are quintrillionbilliongagillion photons traveling the speed of light emanating from the source, see there is no dot, or object moving, it is always individual particles/waves that are moving lightspeed, no object or thing or light is moving faster then light.

perhaps he is not saying it would break if it went light speed, but if it acceded light speed, because if the interactions that work at the speed of light that keeps all atoms and molecules together cannot interact as fast as the material is going, how would the material stay together, is perhaps what he was proposing?

reply to post by swanne


Definitely not fixed.
We know those photons do what they feel.
Don Draper a**ed particles that they are.

reply to post by Arbitrageur


Im having a hard time understanding what is going on with the light on the moon scenario, how it can be going faster then light. In the video it shows the arcing motion, so is this just expressing photons traveling at light speed emanating from a common source, when the source is turned, the collective photons from moment still thru moment turned, cover more space in less time, then an unmoved source? (you know I love analogies but I admit this may be a crap one, but maybe not) the difference between a single shot gun shell, and a buck shot? Or an automatic machine gun stationary firing unlimited, and one firing unlimited but moving side to side. The one moving side to side, after the bullets leave the source, cover are greater distance because of their direction. This is a real confusing one, because I think I know, yet its said from one source of light, the light is traveling faster then the speed of light, I dont know how that can be, even with what weve been saying.

The shadow thing I am also skeptical of, because the information of there being a shadow cant be known until all the light from beyond the source causing the shadow, must be sent through to us at light speed, and hit our eye, and the shadow exists when the last of it has hit our eye, so it still depends on the speed of light. If anything the situation of shadow exists prior then we are aware of it, because we wait to receive the last light that was let through, this does not mean shadows occur faster then the speed of light, this just means the default setting of our eyes and brains is to detect pure black when there is no light, so if there is no light to detect...but now I realize I may be thinking of this wrong.

So say we are in a dark room completely dark standing in the exact middle of a huge room (guess it doesnt matter), And I have a flashlight in my right hand, and I turn it on facing my left hand, you are saying my brain or any detector would detect the shadow of my hand on the wall before any light is detect there or around it? or my eye/brain detects the shadow hand before the light around it?

Arbitrageur

dragonridr
Ok i found the NEC press release on the experiment but still no paper. But ill say CBS just read the labs press release so they got the idea generally i guess.
www.nec.co.jp...

The 3-microsecond long pulse of light would normally take only 0.2 nanoseconds to pass through the chamber in a vacuum. But when passed through the specially prepared chamber, light emerged 62 nanoseconds earlier than it would have had it passed through the chamber in a vacuum.

So, subtract 62 nanoseconds from 0.2 nanoseconds and you get...wait, what? Does that even make any sense?

For example, if it said: "light emerged 0.1 nanoseconds earlier than it would have had it passed through the chamber in a vacuum", then we can calculate it was traveling at 200% the speed of light, which would at least make some sense, sort of. But trying to do the same calculation with the numbers cited yields a negative time interval, something like backwards time travel. Either there's a typo or I'm missing something.

Maybe they forgot the . and its .62 if that would make any sense, but such an important topic you dont think they would make such an error. Or I think it may make sense as is, I think it may be saying 62 nanosecond times earlier maybe. It normally takes .2 nanoseconds, which can be seen for that distance of vacuum the normal average constant, so I believe its saying 62 nanoseconds earlier then that? So maybe it would be .2 divided by 62 which would be 0.00322580645 nanoseconds?