Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 02/08/2016 11:23:02
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Björn Bohman asked the Naked Scientists:
Hi
Thanks for a fantastic show!
A few weeks ago an astrophysicist (I think) was interviewed on your show, and he said something that needs to be talked about more if it's true (and given I heard him correctly). Unfortunately I don't recall which episode it was nor what the actual topic was on which he was interviewed.
Anyway, what he said was that time moves at the speed of light. And he just mentioned it in passing when talking about something else.
That's a terrible thing to say and then not explain why that is, isn't it?? That's many hours of good sleep I won't get back! ;)
Jokes aside, is this really true?!
Cincerely,
A sleep-deprived Björn
What do you think?
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A few weeks ago an astrophysicist (I think) was interviewed on your show, and he said something that needs to be talked about more if it's true (and given I heard him correctly). Unfortunately I don't recall which episode it was nor what the actual topic was on which he was interviewed.
Anyway, what he said was that time moves at the speed of light. And he just mentioned it in passing when talking about something else.
That's a terrible thing to say and then not explain why that is, isn't it?? That's many hours of good sleep I won't get back! ;)
Jokes aside, is this really true?!
No! Not at all. In fact it's not even meaningful to speak of the speed of time. People like that are an embarrassment to all physicists. He either doesn't know what he's talking about or was trying to impress someone.
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Actually, yes it does.
I don't know why you would think otherwise.
I mean, the only way you could disagree with that is you don't like the way it is described. In technical terms, time doesn't ''move'' and if you're hating on that because it was described so simply, I guess you would be right.
However, for practical purposes, yes, time in fact moves at the exact speed light moves. That is the reason why time wouldn't pass at all if you were moving at the speed of light, because you would be moving with time.
That is because time IS in a way the movement of light.
If you flashed a beam of light at a theoretical planet which is 1 light year away, you would see the beam after 1 year, the time it would take light to get there. That is because we define something ''happening'' as seeing it happen. So, a 1000 light year-away star exploding would, in relative terms, happen at your location in a thousand years, ie. after the light of the explosion reaches you.
This is just a matter of definition, so for practical purposes, happening (or time) happens at the speed of light.
So that is a simplified explanation.
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Actually, yes it does.
Please prove it. I.e. please post precisely what he meant by Time moves at the speed of light.
Let me ask you something. Are you a physicist? If not then have you studied special relativity, at least the college level (i.e. calculus based textbook?).
I know of no relativist who would ever think or speak in those terms and I personally know the best of them. And I myself am a relativist. In fact just to demonstrate that I'm not the only person who knows this fact I'll e-mail the most well-known relativists that I know and pose the question to them and ask if I can quote them.
I don't know why you would think otherwise.
You're kidding, right? Why would you even ask such a question when in reality no relativist would ever make such a statement because saying that time moves is meaningless. At least not literally and that's how physicists speak in physics when they make statements like that.
Recall the actual definition of speed and then explain to me how your assertion can be true in light of what the term "speed" means.
To be rigorous we'll define the instantaneous speed of light since that will hold in all possible scenarios. The instantaneous speed of a particle/object is defined as the magnitude of the increment of the particle's spatial displacement ds/i] (where ds = |dr|, r = (x, y, z)) traveled by the particle during the (coordinate) time interval dt. The value is then given by v = ds/dt. However time is not something that is not something that can even be thought of as being localized to the point of it having a position and as such there's no meaning to the notion of time having a spatial displacement, i.e. time can't move. For that reason it can't be said that time has a speed.
I mean, the only way you could disagree with that is you don't like the way it is described.
Not at all! First, please take note of the fact that nobody described it! All that was done here was that someone quoted a blanket statement and didn't give any meaning to it.
The OP posted a sentence which I assume was a quote and in that quote specific terms, i.e. time and speed, were used which have a well-defined meaning in physics. No scientist can claim that he's correct in what he says merely because he chose to redefine the terms that he used in order to construct a sentence that he wanted to say or described a situation in which they thought it could have a rigorous meaning.
In technical terms, time doesn't ''move'' and if you're hating on that because it was described so simply, I guess you would be right.
Then what are you complaining about? In any physics forum, class or any physics discussion, people never speak in any other way than in precise physical terms (what you call "technical"). We don't speak in any other terms in fact.
By the way. Please don't put words into my mouth. Especially the word "hate." In my opinion that term has no place in a scientific discussion.
However, for practical purposes, yes, time in fact moves at the exact speed light moves.
Then prove it. What are these "practical purposes" that you're talking about? Why are you saying all of this stuff and making absolutely no attempt whatsoever to provide a proof of your claim?
If you flashed a beam of light at a theoretical planet which is 1 light year away, you would see the beam after 1 year, the time it would take light to get there.
No you wouldn't. It would take two years, i.e. the time it takes for light to travel to the planet, be reflected and then travel back to you.
That is because we define something ''happening'' as seeing it happen.
Incorrect. Physicists define something as "happening" when we "measure it to happen" not to simply see it happening (i.e. record the presence of light leaving or arriving somewhere)
So, a 1000 light year-away star exploding would, in relative terms, happen at your location in a thousand years, ie. after the light of the explosion reaches you.
That's totally incorrect. Now I don't need to know if you're a physicist or not because a physicist would never think like that. All physicists and especially astronomers and astrophysicists, take into account the time it takes for light to arrive from what they're looking at to determine when something happened. Not doing that would lead to horrendous mistakes in cosmology since we use what we see from distant galaxies in order to look "back in time".
This is just a matter of definition, so for practical purposes, happening (or time) happens at the speed of light.
So that is a simplified explanation.
Except for the fact that not one physicist, cosmologist, astronomer, astrophysicist or any other physical scientist would ever speak in those terms. And I know that as a fact. It's an extremely important part of physics to know that fact. In fact its essential in the derivations of such things as time dilation and length contraction in relativity. Proof is on my website here:
http://www.newenglandphysics.org/physics_world/sr/time_dilation.htm
http://www.newenglandphysics.org/physics_world/sr/lorentz_contraction.htm
http://www.newenglandphysics.org/physics_world/sr/lorentz_contraction_2.htm
http://www.newenglandphysics.org/physics_world/sr/lorentz_contraction_3.htm
It's very clear to me from what you've just said that you really don't know what you're talking about. Sorry. I don't mean to come across as being mean. I'm just saying it like it is. That means that I'm not trying to insult you. I'm merely describing your knowledge and skills. You should read more on the philosophy of science before you go around making incorrect assertions like your false definition of "happening". That means that if you can't find a definition in at least a three very good textbooks then you shouldn't make any claims to it being a fact.
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Except for the fact that not one physicist, cosmologist, astronomer, astrophysicist or any other physical scientist would ever speak in those terms. And I know that as a fact.
Except for the one you mentioned in the post just before this one and many others I've heard.
You have to understand that these scientists are catering to the general audience. They are explaining it in a way that a layman (and not even necessarily that bright of a layman) would understand. Your explanation would offer nothing to them.
I am well aware that time isn't something that literally exists. It's just a measurement of how soon something arrives moving at a certain velocity.
However, since movement is the main factor in determining time and speed of light is the maximum velocity of movement, those two are mathematically linked. So, for example, one would experience no passing of time while moving at the speed of light. On the other hand, one would say that more time has passed if they were standing completely still than if they were moving at any rate at all (the faster they did, the less time they would perceive as having passed).
I fully understand why it is this way but I offered a simplified answer to the layman. Now you will argue that this makes no sense as it is not the most scientifically accurate explanation, so me explaining it to him doesn't technically teach him anything because he can't do any physics with what I said.
I beg to differ:
His understanding of time in physics was lesser than what was explained by me. Your full and extensive explanation would require pages and pages of explanation and links to articles and formulas, and would most likely not result in anything. Therefore, even though my explanation wasn't that scientifically accurate, it explained more to him than yours would.
However, I agree that the example with the star exploding was totally bad and incorrect. I only meant to show the link between time and speed to him in an example, but saying that happening means seeing something happen was totally wrong. You would be correct there.
By that logic, a supernova wouldn't be exploding at the moment it does, but only when the light of the explosion would reach us.
Suggesting that I should read the philosophy of physics is completely preposterous, though. I know that I understand the philosophy of physics.
I used the word ''hating'' only because English isn't my first language and I couldn't find a better word in a hurry.
To be concerned by syntactics so much is meaningless.
Anyways, I don't think I was wrong to use that word anyway, since you were visibly triggered by the first post.
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Except for the one you mentioned in the post just before this one and many others I've heard.
Who was it that I mentioned?
You have to understand that these scientists are catering to the general audience.
Hardly. I'm referring to what they know to be the real physics/relativity. And this comment is irrelevant anyway. You can hardly use such an assertion in a physics discussion because it can't be proved.
They are explaining it in a way that a layman (and not even necessarily that bright of a layman) would understand.
I'd never ever ever say something like that to a laymen because it'd be a deception. Once the layman moves on to more rigid textbook physics they become angry at people who've misled or lied to them in that way. I know I do.
I am well aware that time isn't something that literally exists. It's just a measurement of how soon something arrives moving at a certain velocity.
The stop claiming that I'm wrong and that what that guy said was right. You're not only wrong but you're misleading them. In any case you have yet to explain to the OP what that guy meant when he made that assertion. He had to have meant it to be taken literally since claiming time moves at the speed of light requires a calculation and quantitative statements don't.
Are you going to provide the meaning of what such a statement is supposed to convey and a source where it can be found in the physics/relativity literature? If it can't be found in the literature then you've never seen it and don't know what it means.
So, for example, one would experience no passing of time while moving at the speed of light.
A good relativist would never make such a statement because it can't be done since its impossible. And no observer will ever see his watch slowing down or stopping because time dilation is a relative phenomena meaning that its what one observer measures another observers clock to be doing compared to his own. This is meaningless for an observer moving at the speed of light. That's precisely why you'll never see a relativist mention it in a textbook.
Suggesting that I should read the philosophy of physics is completely preposterous, though. I know that I understand the philosophy of physics.
Not from what I've seen you post, you don't.
I await your explanation of what "time moves at the speed of light" means and how the speed is determined to be "c" and not some other value. If you don't then this will be my last post. I can no longer tolerate your constant claims about what physicists mean when the say something. It's all wrong, every word of it. That's what comes from actually being a physicist/relativist rather than reading a book or two on the subject and thinking you know it all. I noticed that you refused/chose not to answer my question about your education in physics and/or relativity. I'm not asking anything unreasonable. I'm merely asking precisely what your sources are. You keep making claims which you refuse to justify and I don't waste my time reading that kind of post so this is probably it for me.
Björn Bohman - The answer to your question is No! It's very very far from being true in any sense.
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There is a rate at which time dilates when moving between unequal potentials in a gravitational field. This is however observer dependent. The ideal observer being at infinity. This gradient does not equal a speed for time as it would be defined as time over potential. These are the wrong units for speed. You cannot fix time at a point in space since you can't stop time
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time moves at the speed of light
Time moves at the rate of 1 second per second.
At least this measure has consistent units... [:)]
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I don't think it's a very useful concept. As I understand it, any object moves through spacetime at the speed of light.
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I don't think it's a very useful concept. As I understand it, any object moves through spacetime at the speed of light.
Whoever gave you that idea misled you. Its based on the flawed concept that there's such thing as actually "moving" through time. Only motion through space has meaning since that's what motion means. What you're referring to is hinged on misnaming the spacetime interval as "distance in spacetime". Distance is only defined according to spatial increments. The phrase "distance in spacetime" is merely an analogy and should not be taken to be more than that or its an abuse of the concept of the spacetime interval.
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The term "speed of time" has no logical meaning. The word "time" refers to the passage of events only and when scrutinizing different events, we record the sequence of those events using the standard second. If as you ask: "Does time move at the speed of light?", what are we to make of the theoretical Tachyon who's speed is always faster than c?
If time only moves at the speed of light, then the theoretical existence of the Tachyon wouldn't have any merit.
Considering that the Tachyon is a theoretically recognized particle, every physicist that considers their possible existence should re-evaluate their reasons for investing in such a theory.
Time has no speed my friend, it is only a reference marker between sequential events.....................
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You know, I am not quite sure I really understand space time. Whats more I sort of doubt anybody does, so it might be a good idea to approach the topic with a little humility. This is my take.
As far as I can figure it everything travels at the speed of light. Photons and probably neutrinos directly and the rest of the fundamental particles as standing waves. As everything else is made of those particles then C is sort of the only speed there is. Lower speeds are a mathematical convenience but add all the vectors together and you should get C every time. That's what time dilation due to velocity is all about- the faster an object travels in space the slower it must travel in through all the ways it does when we think of it as "at rest" and together correspond to aging.
There is some question about what time actually is. It is a dimension. It might be, except from our point of view, no different from the 3 dimensions of space. I tend to think that it is a specific direction locally. That is for this particular position space, space itself has a rest velocity. Difficult to get away from the idea with the big bang theory. Anyway, right here there is a vector in the 4 dimensions of space time that we can call time and corresponds to the direction entropy takes. Go far enough, in accordance with the Hubble constant, the direction will be different.