| Davini994
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| 215939. Tue Oct 02, 2007 11:52 am |
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| dr.bob wrote: | | [light]consists of both electromagnetic oscillations coupled with mechanical oscillations of the charged particles that make up the medium. |
Huh? |
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| npower1
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| 215961. Tue Oct 02, 2007 1:27 pm |
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Davini994,
Dr bob has probably gone home now so I'll give this a whirl.
Actually, can I suggest reading the 'Surpassing Light' thread under General Banter. If, or when, you have and you still have 'Huh' I'll be quite happy to try to clear up that 'Huh'. |
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| Davini994
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| 216138. Wed Oct 03, 2007 4:42 am |
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Just so you know npower, I'm a Theoretical Physics graduate.
The surpassing light thread doesn't mention the cause of the 'huh' I'm afraid.
Having thought about it, I think the cause of the confusion is the usual one between dr.Bob and myself: language. Dr Bob being very much the Astronomer and myself Theoretical Physicist;)
Having thought about it, I'm now thinking that he just means the effects that the photon has on the medium it's travelling through, and is calling all of that 'light'. Which makes a lot more sense if I'm right, although I wouldn't phrase it like that. Right Dr Bob?
Flipping semantics. |
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| dr.bob
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| 216205. Wed Oct 03, 2007 7:39 am |
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Yeah, that's pretty much it. When talking about the speed of light in a medium, it's a bit more tricky to measure the actual speed of light itself because of all the interactions with the medium along the way.
That's what I was kinda getting at. |
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| Davini994
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| 216475. Wed Oct 03, 2007 4:25 pm |
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| npower - sorry, didn't mean that to sound as much like a put down as it does. Thanks for being helpful. |
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| npower1
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| 216514. Wed Oct 03, 2007 5:49 pm |
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It was sort of embarrassing. There was me, without a scientific qualification (except for a degree in computer science as defined long ago) being willing to educate you in what turns out is your professional expertise.
This is actually quite strange. It also points out, and draws attention, to the 'difficulty'. This is how does the scientific community ensure that the general population appreciates science and its basic methods. |
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| Davini994
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| 218820. Tue Oct 09, 2007 11:52 am |
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Good question. I suppose 'populist' books like A Brief History Of Time. Lots of physicists have tried to do similar things, and it's a bit of a hot topic. "Each equation halves the sales of the book" is an oft quoted phrase by authors of the genre.
Much as I hesitate to mention it again, but Bill Bryson's book covers a lot of interesting concepts, without getting counnecessarily and confusingly technical at all. I certainly learned a lot from it, and have read it several times.
I shall try to restrict my "huh?" posts in future! |
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| npower1
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| 218889. Tue Oct 09, 2007 3:01 pm |
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I didn't actually think that a Brief History of Time was particularly good. I'm sure most copies have probably not been completely read.
Bill Bryson's book was good except he managed to use some technical words early on (possibly assuming they were well known).
The list and and quality of populist books is growing.
My own experience is of learning most of my science knowledge from this type of book. For anyone picking up such a book the best advice is that when you come across a bit that doesn't make sense to you just carry on reading - you almost certainly won't need this specific piece of knowledge to understand the rest of the book. |
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| Davini994
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| 219158. Wed Oct 10, 2007 8:46 am |
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| npower1 wrote: | | I didn't actually think that a Brief History of Time was particularly good. I'm sure most copies have probably not been completely read. |
I don't think there is much doubt about that! My degree was basically that book, with a big pile of maths on top for added fun. Lee and Herring used to do a sketch about it; "chapters 4 to the end might as well be blank because no one gets past chapter 3".
| npower1 wrote: | | Bill Bryson's book was good except he managed to use some technical words early on (possibly assuming they were well known). |
What were they?
The problem with theoretical physics to the layman is that the concepts and conclusions are so based on mathematics so much. It's therefore difficult to get it into common sense terms, lies to children. It's so damn complicated too, and the further you go the more complicated it gets.
Add to that that half of the disciplines are barely understood by the participants (standard model and high energy particles in particular),and it all gets jolly tricky indeed.
Like I say I spent 4 years working on the subject, but I haven't got a clue about half of it. |
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| Neotenic
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| 219160. Wed Oct 10, 2007 8:55 am |
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I have an ebook copy of A Brief History of Time. I think I've mentioned elsewhere that it is possible to get Acrobat to read pdfs out loud to you.
Seeing as the electronic voice rather closely matches Prof Hawkins magic box, the results are probably more amusing than they really should be. I did actually find the content much easier to follow than I thought I would, though - but I freely admit that I didn't get anywhere near the end. |
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| npower1
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| 219205. Wed Oct 10, 2007 11:04 am |
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Davini994 wrote
I can't remember what the words were, nor do I have a copy of the book. They just struck me as not consistent with the level that Bryson was aiming at (and achieving throughout the rest of the book). Whilst I wasn't put off reading the rest of the book someone who may have been using this book as their first 'self educating in science' foray may have been. |
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| gruff5
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| 221301. Wed Oct 17, 2007 4:01 pm |
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Dr Bob said:
| Quote: | The two are completely separate phenomena. The twins paradox is about time travelling more slowly if you're travelling very fast, as explained in Special Relativity.
The water tower thing is about time travelling more slowly in the presence of gravity, as explained in General Relativity.
But you're right, the watch at the bottom of the tower will run more slowly because it's in a (marginally) stronger gravitational field. |
Are they really completely separate, though Dr Bob? For the twins paradox, you could say "aha, all motion is relative" so that the planet Earth is really travelling very fast away from the spaceship and so it should be the twin who stays at home that ages slower. This metaparadox is resolved when you figure in that the spaceship has to accelerate away from the Earth and decelerate to arrive back.
Now, didn't dear Albert say that acceleration is exactly indistinguishable from a gravitational field? So, somehow the acceleration (which has same effects as gravity) has to be figured into the twins time dilation paradox.
But then the acceleration can't be the whole story since if the spaceship cruised steadily for 5 years the time dilation would be much greater than it would be for 1 day of cruising.
Can anyone shed light (no pun intended) on this?
[/quote] |
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| dr.bob
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| 221356. Thu Oct 18, 2007 3:34 am |
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| gruff5 wrote: | | Now, didn't dear Albert say that acceleration is exactly indistinguishable from a gravitational field? |
Yes he did. However, if you consider the acceleration effects required to return the travelling twin home, there is no paradox.
The whole point of the twins paradox is that all motion is relative. Thus, the twin on the earth sees the travelling twin staying younger, while the travelling twin sees the twin on earth staying younger. If you bring them back together again, they can't both be younger. That's the paradox.
This is solved by the application of the necessary acceleration which is the other effect I referred to. It's impossible to get the travelling twin back home without accelerating him at some point. Acceleration is not relative, thus the two twins do not experience the same effects. |
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| gruff5
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| 221523. Thu Oct 18, 2007 9:02 am |
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Thanks for the reply, Dr Bob, but I'm still somewhat puzzled.
Are you saying that the time dilation only happens during the acceleration/deceleration phases? Would this mean that the spaceship that cruised at (very) high speed for 5 years would have the same amount of time dilation as one that cruised for only 1 day?
Are such acceleration affects behing the lifetime extensions of mesons coming down to earth from cosmic ray collisions, rather than their high speeds as such?
As an aside, I heard that some of the Apollo astronauts put in a (tongue-in-cheek) claim for 1 milliseconds overtime as a result of relativity considerations. I would have thought they should have been 1 millisecond *younger* so that they should have been reimbursing NASA! Or was it the lowered gravitational field effects they were thinking about, rather than high accelerations/speeds? All very confusing! |
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| dr.bob
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| 221558. Thu Oct 18, 2007 10:28 am |
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| gruff5 wrote: | | Are you saying that the time dilation only happens during the acceleration/deceleration phases? |
No.
Time dilation happens when travelling at high speeds.
However, all motion is relative. Thus, if I'm travelling at high speed away from you, I will look at you and see you travelling at high speed away from me. Thus we'll both see each other remaining young while we age.
The acceleration of one or other of us is what decides which one of us actually gets older when we finally meet up again to compare notes. |
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