xyzt

I agree, there was no need for the heavy handed intervention by ydoaPs.. I would expect an admission of not understanding the subject matter and an apology.

It is exactly the behavior he criticized me for that he exhibited (to a much greater extent) , especially in the context of his being wrong.

You said "you can measure it with an accelerometer SO you know exactly who is accelerating and who's not". That word "so" there is used in such a way to imply that the second clause is somehow causally dependent upon the first clause.

 

 

 

 

 

 

 

Look,

You still don't get it and you are behaving in a manner that is unfitting for a moderator. Let me try to explain one more time (not for your benefit, since you won't admit to error).

In the twins paradox (which was the context of the discussion) , with the help of an accelerometer, the twins can tell the accelerating twin from the inertial one.

It is precisely because we can measure acceleration with an accelerometer that we know who is and isn't moving. Yet, that's not actually true, since the reading could quite possibly be from a stationary observer in a gravitational field.

Nice try but this was not the context being discussed. Bill and Bob are the twins, one is accelerating away, the other one is not. There is no "gravitational field". If the twins are stationary, then there is no separation and there is no paradox.

That's what your initial post said. Do you understand it yet?

I understand that you do not understand, yet you are acting in a manner that is unbecoming for a moderator. Especially since you are wrong. One more thing: don't talk down to me and don't threaten.

 

So what I quoted from you wasn't quite correct.

Err , I am under the impression that you do not even understand my initial post. It has absolutely nothing to do with being able to tell the difference between the effects of a gravitational field and of acceleration.

When I said that acceleration is "absolute" (as opposed to velocity), that means that you can ALWAYS tell, with the help of an accelerometer, if you ARE accelerating or NOT. By contrast, you cannot tell if you are in uniform motion. I made it quite clear:

You can measure it with an accelerometer, so you know exactly who's accelerating and who's not.

Perhaps I should berate you now. That's how we play here? We berate people trying to learn over inaccuracies until they want to leave?

Not very becoming for a moderator. Especially in the context of clearly having misunderstood the post you are attempting to criticize.

How can you tell the reading on your accelerometer from proper acceleration from a reading on your accelerometer from being in a gravitational field?

If the gravitational field is uniform and if the proper acceleration is constant, the principle of equivalence teaches us that we cannot tell one from the other.

If the gravitational field is not uniform, then we have an effect called "tidal" , i.e. there is a transverse "squeezing" of the accelerometer, an effect that cannot be mimicked with uniform acceleration.

Thank you for actually asking an interesting , intelligent question that takes this thread out of the cesspool it had descended.

Cut it out xyzt.

 

You being nice to people just seems...weird !?!?

Well, it happens very seldom that I get a honest reply to my criticisms. Normally, I get a crank run-around.

This is, of course, what I meant, but it's good to be specific, so thank you for making that distinction clearer than I did.

This is the best example of a measured, rational, answer. No attempts at diversion, further elaboration, introduction of further complications, etc. You got my +1 for that. Too bad that there aren't more like you in this forum.

 

Special Relativity (1905) was before General Relativity (1915).

He's been told that (and many other things).

What you are trying to do is determine the elapsed time in Bill's frame from Bob's frame. That can only be done once there is an acceleration involved, and both Bill and Bob are back together in the same frame.

Actually both Delta and I have pointed that out. Repeatedly.

This applies to translational ( moving ) frames and gravitational frames.

Correct.

You would do well to take some of xyzt's advice, and pick up an introductory textbook on special relativity. The math is not very complex, and it should answer most of your questions.

Thank you. Apparently the moderators found my well-intentioned and appropriate suggestion insulting. This forum has turned into a battle between mainstream people and cranks, with a very heavy dose of threads that are fringe. I will be hard pressed to name a thread that was not started by a fringe set of claims.

If you are at the bottom of a very strong gravity well, you can tell that you are and that you are the one that time is dilating for.

 

Everything else that you posted is correct, except the above. You cannot tell that you are in a gravity well. Your clock ticks at the same rate, of 1 second per second. Clocks do NOT 'slow down" in gravity wells, this is an unfortunate, widespread misconception. Clock ALWAYS tick at their native rate, otherwise they would be worthless as clocks. What happens in reality is that when clocks are observed by a remote observer they appear to "slow down" (to an observer "higher" that the clock in the gravity well or to "speed up" , for an observer "lower" that the clock. This is the main reason why the atomic clocks mounted on the GPS satellites need to have their frequency adjusted down at launch: such that their time stamps line up with the time of the Earth bound clocks.

If someone went to the surface of that planet his time perception would be very different from the time perception of someone on earth.

That is false, clocks tick at the same rate all over the universe: 1 second per second. You simply repeat the same misconceptions over and over in a slightly different way.

Let's say that Matthew Mcconaughey's character had set up a lab while he was there, with a nice telescope and all the staff and instruments necessary to measure the age of the universe, would he have discovered that it was 13.82 billion years old?

Yes, all observers agree on the age of the universe. This is the second time you are being told that. You seem to have a hard time accepting it.

xyzt, It's called a hypothetical situation, and it's used in something called a thought experiment. Yes it's like pretending.

It is called GiGo (Garbage In , Garbage Out)

You're a complete asshole.

You must be talking to your mirror again.

And what are you even doing on this forum?

Keep crank posts to a minimum.

I clearly did not assert that it were possible to teleport instantaneously.

"Assuming that we could teleport instantaneously....". This just only one of the fringe things you posted.

I clearly did not ask if it were possibly to teleport instantaneously.

You didn't ask, you asserted. Amongst other fringe claims.

A follow up question I have: Here on earth we perceive that the Universe is 13.82 billion years old. Assuming that we find a habitable planet somewhere in the universe, and assuming we were able to teleport there instantaneously,

You cannot teleport "instantaneously". You cannot even travel at the speed of light.

once we arrived on that planet, could we measure the age of the universe and find that it is much older or much younger for that planet?

Neither, if you understood what was explained to you, you would have understood that the the age is still 13.82, speed has no effect.

Might there possibly be planets in this universe that are presently existing only 1 billion years after the big bang? Might there be planets that are presently existing 200 billion years after the Big Bang?

No.

Your hunch is wrong. If you had bothered to follow any of the discussion in this and related threads, you would see why.

 

———————————————

 

I had a conversation at work the other day. A colleague had been trying to figure out why two devices were giving the same signal, when there was an effect that should make them different. I realized there was a second difference between the two, and the effects should cancel. He paused, and said, "Oh yeah. I hadn't thought about that." He was happy. He learned something. (many times the roles have been reversed in this kind of conversation). He went and told someone else why it's OK the signals were the same.

 

It was refreshing.

 

Because he didn't ignore my correct observation. He didn't double down on his insistence that the signals should be different. He didn't posit a hunch that all of the science was wrong. He didn't ignore the math. He didn't try and come up with a more convoluted scenario, or redefine the terminology, to try and sneak some way he could be considered right into it. He didn't leap ahead into an even more advanced area of science, without having understood more basic phenomena.

 

It was refreshing, but not surprising, because it was science and not crackpottery. Such discussions are one of many reasons I've enjoyed working in science, both in research and teaching.

 

[/morality play]

It does happen (in real life, with real scientifically minded people). Not very often in this forum where trolling and time wasting is "du rigueur". Where is the fun in accepting a rational, scientific, rigorous explanation when you could stretch the thread on 10 more pages?

 

Don't mind xyzt, he is like that with everyone. But he does know his stuff....

 

 

So, if we ignore acceleration (and therefore never bring the spaceship back to Earth) then Bill will see Bob age more slowly that him, and Bob will see Bill age more slowly.

 

This is not quite right. Bob measures an em ray sent by Bill as redshifted (Doppler). Bill measures an em ray sent by Bob redshifted by the same amount. Nothing to do with total elapsed proper time. Proper elapsed proper time omes into play only when the twins are reunited via some mechanism and they can compare clocks side by side.

Dingle mixed the mutual time dilation with the twins paradox. The two are two DIFFERENT effects of SR.

And if you do bring Bill back to Earth, then he will have experienced less time and will be younger than his "twin" on Earth. This is a bit subtle but the Wikipedia page has quite a good explanation

Correct. I wrote a big chunk on that page.

That was annoyingly arrogant, incredibly rude, and profoundly unhelpful.

 

I simply pointed out that you lack the basics for tackling more advanced issues. <shrug>

If someone is traveling at light speed relative to earth (but not accelerating) does he age slower than someone on earth? If so, why?

No one can travel at light speed.

Even if that person did, by absurd, he or she would NOT "age slower".

Still, i'm confused about time dilation. Einstein FIRST came up with general relativity, which correct me if I'm wrong, only has to do with speed, NOT acceleration. It wasn't until special relativity that he addressed changing speeds. Right?

 

 

Wrong. Have you tried actually studying the subject?

So lets ignore the acceleration part for a minute. Imagine a woman is in labor on a spaceship going 95% light speed. She gives birth to baby Bill right as they pass earth. There is another woman on earth who gives birth to baby Bob right as the spaceship passes overhead. The spaceship continues on at 95% light speed (relative to the earth of course).

 

30 years passes on earth and Bob is now 30 years old. How old is Bill?

 

According to explanations I have seen, Bill would be only a few minutes or hours or perhaps days old, because time would be much slower for him traveling near light speed.

Wrong again. Bill is also 30 years old. Look, you are grappling with the so-called "Twin Paradox". Understanding it requires a fairly good understanding of special relativity. You do not have that.

So when we take into account "there is no speed but relative speed" it seems like Bob would age quickly from Bill's perspective, and Bill would age quickly from Bob's perspective. Which is just silly because that means that When Bob is 30 he thinks Bill is only minutes old, and when Bill is 30 he thinks Bob is only minutes old.

Here you are struggling with mutual time dilation, or the so-called "Dingle paradox". This is not a paradox , it stems from the lack of understanding of basic SR.

But if speed is only relative then I don't understand time dilation.

The twins "paradox" that you are grappling with has NOTHING to do with time dilation. You have way too many misconceptions about relativity, you should consider a class. Start slowly, from the basics, only AFTER that you can tackle the more advanced subjects.

Thank you for your reply!

 

But if there is no absolute speed, only speed relative to another body, wouldn't that mean that acceleration is relative as well? If Bill "accelerated" away from Bob, couldn't it be said that Bob "accelerated" away from Bill?

No, acceleration (proper acceleration , more correctly said) is absolute. You can measure it with an accelerometer, so you know exactly who's accelerating and who's not.

any internet links? what about applying it to earth rotation ?

Here

here

suppose we have disk fixed to its edge a string in which a mass is hung, when the disk rotates the mass will start rotating as well in an opposite direction of the disk, if the disk rotates clockwise the hung mass will rotate counterclockwise and vice versa, i tried this by myself and anyone can try it by holding a string and rotating it around yourself the mass fixed to it will rotate in an opposite direction , if we suppose instead of the disk the earth itself rotates, that will lead in "every object hung in a string will rotate due to earth's rotation around its axis!!" this rotation will be slight and will disappear at the equator .

 

when we rotate the disk the mass will start to rotate after a while the string will store some potential energy due to the rotating of the mass.

 

yes, it is called conservation of angular momentum, sorry to burst your bubble, it isn't a new phenomenon

That you reject them out of hand suggests to me you are not, but simply trolling.

Obviously. His posts are either content free or outright nonsense.

Not since I've started the thread, no. Does it mention about doubling the effect does it? I'll have another look.

Yes, it does. You need to follow the math.

If "the target moves" the gun moves too doesn't it?

They move in OPPOSITE directions. This DOUBLES the effect. Have you watched the video? Did you bother to read the wiki article on the Coriolis effect? Sigh.

 

"the target moves"

Sigh....

 

Didn't xyzt's post answer this in sufficient detail?

Sigh.....