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Relativity


Dave McReynolds

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Dave McReynolds

I've always been interested in relativity, at least when it's dumbed down to the extent a retired CPA can make some sense of it. I understand that the passage of time is relative to the relative speed of objects to each other. In other words, if an object is traveling very fast relative to us, an hour there may be equivalent to a year here, as all of us who have watched the movie Interstellar know. Gravity plays a role in this also, but let's not overcomplicate things.

 

What I've never heard addressed is whether there is such a thing as an instant of time, which is the same wherever you are in the universe, whatever speed you're going. Does that same instant exist throughout the universe? So when I pressed the first key of this post, did someone in a galaxy 8 billion light years away from us that is receding from us at 10% of the speed of light also experience that same instant at the same time I did, even though 5 minutes later in our time, only 1 minute might have elapsed there? Or, expressed maybe more scientifically, if, when I pressed the first key of this post, the universe was exactly 13 billion, 800 million, 4 hours and 3 seconds old here, did that same instant occur everywhere in the universe at the same time it did here, so the universe was exactly the same age at all points in the universe at that exact moment? So at that moment, regardless of the rate time might be passing relative to any other place in the universe, we were all the same point relative to what was past and what was future?

 

It seems that if that is true, time might be a little less relative than I thought it was.

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Does that same instant exist throughout the universe? So when I pressed the first key of this post, did someone in a galaxy 8 billion light years away from us that is receding from us at 10% of the speed of light also experience that same instant at the same time I did, even though 5 minutes later in our time, only 1 minute might have elapsed there?

 

I am not a physicist, but I believe the answer is no. I think you're asking if there's an equivalent of Greenwich Mean Time for the universe.

 

Check out this reference:

https://en.wikipedia.org/wiki/Relativity_of_simultaneity

 

From that page, "According to the special theory of relativity, it is impossible to say in an absolute sense that two distinct events occur at the same time if those events are separated in space."

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Dave McReynolds

Does that same instant exist throughout the universe? So when I pressed the first key of this post, did someone in a galaxy 8 billion light years away from us that is receding from us at 10% of the speed of light also experience that same instant at the same time I did, even though 5 minutes later in our time, only 1 minute might have elapsed there?

 

I am not a physicist, but I believe the answer is no. I think you're asking if there's an equivalent of Greenwich Mean Time for the universe.

 

Check out this reference:

https://en.wikipedia.org/wiki/Relativity_of_simultaneity

 

From that page, "According to the special theory of relativity, it is impossible to say in an absolute sense that two distinct events occur at the same time if those events are separated in space."

 

That's interesting. I wasn't really suggesting that there was such a thing as GMT for the universe, because GMT would only be constant for things going at the same velocity as the earth. What I was suggesting was that if I define an instant here on earth, that instant would exist throughout the universe, even if relative times are not the same before and after that instant, because of different relative velocities in different places. What your source suggests is that observers in different locations would conclude that actions in different places occurred at different relative times. That is one observer would conclude that A happened before B, while another observer would conclude that B happened before A. And both would be correct.

 

So I can't conclude that when I pressed the first key of my post, that that coincided with certain things happening at that same time in the rest of the universe. Because there is no such thing as "same time."

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Dave McReynolds

Along the same lines, we are now able to detect light from objects that emitted that light more than 13 billion years ago, or close to the time the universe was formed. However, because of expansion of the universe, it is estimated that the objects that emitted that light are now actually more than 20 billion light years away from us, a seeming impossibility. Evidently not, as I guess the expansion of space itself is not limited to the speed of light, as objects within space are.

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So I can't conclude that when I pressed the first key of my post, that that coincided with certain things happening at that same time in the rest of the universe. Because there is no such thing as "same time."

 

Well said. Maybe I should have said "Star Date" instead of GMT. :grin:

 

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One thing we can say for certain, some of us have more time on their hands than others. :grin:

 

Your questions are interesting. I've been interested in astronomy for many years and have read a lot of articles about space/time.

 

I've still had a hard time wrapping my head around the idea of someone leaving earth, traveling thru space and then returning only to find everyone else has become old or died while they did so at a much slower rate.

 

The only thing I can relate to is that we all have less time to live than we did yesterday.

 

If you put of ridding till tomorrow, that's one less day you will ride in your life time. :wave:

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Joe Frickin' Friday
I understand that the passage of time is relative to the relative speed of objects to each other. In other words, if an object is traveling very fast relative to us, an hour there may be equivalent to a year here, as all of us who have watched the movie Interstellar know. Gravity plays a role in this also, but let's not overcomplicate things.

 

Fun fact: GPS has to be corrected for general and special relativity. Interestingly, the correction for gravitational effects is much larger than, and in the opposite direction of, the correction for motion. Without those corrections, GPS would quickly become useless, accumulating 10 km of error every day.

 

Because an observer on the ground sees the satellites in motion relative to them, Special Relativity predicts that we should see their clocks ticking more slowly (see the Special Relativity lecture). Special Relativity predicts that the on-board atomic clocks on the satellites should fall behind clocks on the ground by about 7 microseconds per day because of the slower ticking rate due to the time dilation effect of their relative motion.

 

Further, the satellites are in orbits high above the Earth, where the curvature of spacetime due to the Earth's mass is less than it is at the Earth's surface. A prediction of General Relativity is that clocks closer to a massive object will seem to tick more slowly than those located further away (see the Black Holes lecture). As such, when viewed from the surface of the Earth, the clocks on the satellites appear to be ticking faster than identical clocks on the ground. A calculation using General Relativity predicts that the clocks in each GPS satellite should get ahead of ground-based clocks by 45 microseconds per day.

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I believe the answer would be something that is happening at one point in time is equal anywhere. That said, this point in time is this point in time, distance only changes the perception thereof. But since it could also be argued that time is a man made concept relevant only to man's understanding of the universe then you could say,,,,

 

hey there's a squirrel ...

Edited by Sonor
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This all reminds me that I am too feeble-minded to even try to comment on such things.

 

The last time I attempted to get into something related to physics, I was in a limo with five other guys, after the Scotch Whisky Extravaganza in Chicago. Somehow, I was inspired by the whisky to try to explain a paper that a friend of mine had written on Bell's Theorem and the question of whether it truly contradicted Eienstein's Special Theory of Relativity.

 

I was doing pretty well, until another gent in the limo piped up and said, "That's almost right . . . " and proceeded to explain how what I was saying was, well, almost completely wrong.

 

It turns out that he was a former professor of physics at Purdue University and the Chief Technology Officer of a major telecom company. He knew just a wee bit more about physics.

 

Carry on, folks.

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"So when I pressed the first key of this post, did someone in a galaxy 8 billion light years away from us that is receding from us at 10% of the speed of light also experience that same instant at the same time I did, even though 5 minutes later in our time, only 1 minute might have elapsed there? "

 

Yes, but only because that someone made you do it.

 

landofgiants.jpg

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I believe that is exactly the point to the theory of relativity: Time is relative to speed. So no, there is no standard time instant. Time cannot be separated from speed.

 

So if you're travelling in your car at the speed of light, and you turn your headlights on, do they do anything?

 

Answer is that it's a trick question. We can't actually go the speed of light.

 

OK then. Suppose that you can go VERY close to the speed of light in your car. Well at a super high rate of speed, time has slowed way, way down for you. So you turn on your headlights and they work just fine.

 

But what the hell do I know? I don't even have a car.

Edited by elkroeger
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A physics professor once explained that relativity/spacetime warp etc etc can only be accurately represented by mathematical equations. Endeavoring to describe these concepts verbally is imprecise at best because our language and observational experience lack a common frame of reference.

 

Compare it to trying to describe the color chartreuse to a person who has been blind from birth, or A fifth of

to one who was born deaf.

 

Accordingly, without a MS in mathematics, the difficulty we experience trying to understand the concepts is unavoidable.

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Dave, if you get suited up, and get your bike ready for a long ride, and leave just as the sun is coming up, perhaps tomorrow morning. If you beat the traffic, and get out of town on some good riding roads, in a few hours, the answers to this, and other mysteries will come to you.

 

Enjoy the ride...

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Dave McReynolds

I suppose you could force the issue, couldn't you? Let's say the age of the universe, measured from earth, was 13 billion, 800 million years, 3 hours, and 35 seconds at the instant I started typing this post. Couldn't you define that instant as occurring at the same time anywhere else in the universe, when the age of the universe measured at that place was that same exact number? Even if it is impossible to measure the age of the universe that precisely, as a concept, it should be possible to define an instant as being the same at any two points in the universe when the age of the universe, as measured at each of the two points, is the same. How would relativity deal with my concept?

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Dave, if you get suited up, and get your bike ready for a long ride, and leave just as the sun is coming up, perhaps tomorrow morning. If you beat the traffic, and get out of town on some good riding roads, in a few hours, the answers to this, and other mysteries will come to you.

 

Enjoy the ride...

 

Corollary #1 to the ride - enlightenment theory is that unlike relativity, the faster you go, the faster enlightenment occurs.

 

And yes, the man in the woods is wrong. The sooner you accept it, the sooner you will achieve peace in your home. 😀

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  • 5 weeks later...

I have long held that time is not a dimension at all, but not having the brainpower to support this beyond the "I say so" stage haven't made any progress beyond that hunch. I'm not alone in this thought, there are many able physicists that suspect the same thing and books have been written about it.

 

So, if time is in fact a series of discrete 'states of the universe' the answer to your question about a 'moment in time' would be yes, the universe was in one state at one 'time'.

 

Today I discovered that my thoughts have actually been published as a scientific paper (though they were thought by much cleverer people than me). It's just a hypothesis, nobody is claiming absolute truth here yet so let's not get into that aspect of it.

 

Interesting article in layman's terms with a link to the paper

 

http://futurism.com/is-time-really-a-crystal-physicists-upend-quantum-mechanics-and-philosophy-with-new-idea/

Edited by Killer
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Dave McReynolds

Interesting. So what is proposed is that time is a series of discrete still images, like a movie. However, in a movie, it is possible to measure the gap between the still images by a concept that we call "time." If time IS the still images, then what is the gap between them?

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Interesting. So what is proposed is that time is a series of discrete still images, like a movie. However, in a movie, it is possible to measure the gap between the still images by a concept that we call "time." If time IS the still images, then what is the gap between them?

 

24 frames/second

 

MB>

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Interesting. So what is proposed is that time is a series of discrete still images, like a movie. However, in a movie, it is possible to measure the gap between the still images by a concept that we call "time." If time IS the still images, then what is the gap between them?

 

Well, that is another mind bending question. This paper proposes that the shortest time possible is considerably longer than previously theorized which was the Planck time (the time light takes to travel the shortest quantized distance). I don't think they were specific about the measurement but I haven't read the whole paper (don't understand it). The current proposed quanta of time is about 10 to the -43 seconds, or pretty short! However, we must understand that seconds are a human invented measurement of time, there really isn't any time in between the states in the time crystal, what we call time is a count of the number of states that have passed between any two or more states we can observe.

 

I no longer trust the kitchen timer...

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I no longer trust the kitchen timer...

 

 

Killer's conclusion is the "bottom line" and something I actually understand after reading this post! :grin:

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  • 2 weeks later...
I suppose you could force the issue, couldn't you? Let's say the age of the universe, measured from earth, was 13 billion, 800 million years, 3 hours, and 35 seconds at the instant I started typing this post. Couldn't you define that instant as occurring at the same time anywhere else in the universe, when the age of the universe measured at that place was that same exact number? Even if it is impossible to measure the age of the universe that precisely, as a concept, it should be possible to define an instant as being the same at any two points in the universe when the age of the universe, as measured at each of the two points, is the same. How would relativity deal with my concept?

No. Because there is no way to measure or even observe that instant. The instant isn't the same at those other place/times.

It's sort of like being in a fun house where the mirrors change shape constantly. Which is the "real" reflection?

The Simultaneity thing is hard to analogize. What Rex R posted about needing to be able to understand the math concepts is right on. It simply isn't accessible to us reg'lar people.

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Dave McReynolds
I suppose you could force the issue, couldn't you? Let's say the age of the universe, measured from earth, was 13 billion, 800 million years, 3 hours, and 35 seconds at the instant I started typing this post. Couldn't you define that instant as occurring at the same time anywhere else in the universe, when the age of the universe measured at that place was that same exact number? Even if it is impossible to measure the age of the universe that precisely, as a concept, it should be possible to define an instant as being the same at any two points in the universe when the age of the universe, as measured at each of the two points, is the same. How would relativity deal with my concept?

No. Because there is no way to measure or even observe that instant. The instant isn't the same at those other place/times.

It's sort of like being in a fun house where the mirrors change shape constantly. Which is the "real" reflection?

The Simultaneity thing is hard to analogize. What Rex R posted about needing to be able to understand the math concepts is right on. It simply isn't accessible to us reg'lar people.

 

Aside from the difficulty (or impossibility) of measuring the age of the universe precisely, its age has been estimated to be around 13 billion years. Are you saying that the universe has no definite age at any given point in space? In other words, could two observers standing next to each other measure the age of the universe, and each come up with different answers, and both be correct? If that is so, does the estimate of 13 billion years have any validity?

Edited by Dave McReynolds
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First you would need to define when time began. If time began when the universe began then it has a valid age, if two observers standing next to each other came up with different ages one of those observers would be wrong.

 

Terry

Edited by terryofperry
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