Question about aging and near light speed travel

[Sweater of AV]

Einstein proved that moving clocks slow down.

Einstein postulated that motion slowed time in the early 1900s.

Just to point something out that creates a lot of confusion. "Moving clocks slow down" and "motion slows time" aren't the best phrases to use. No inertial frame is "moving" any more than another. They are all moving relative to each other.

Time dilation in its simplest form refers to the fact that if two events occur at the same location in one inertial frame then any frame moving relative to it will measure a longer time between those two events. The clocks are operating perfectly normal in each frame and time isn't slowing down in either frame. They just measure different spatial and temporal values for the events that occur.

 

[Andy Capp]

Just to point something out that creates a lot of confusion. "Moving clocks slow down" and "motion slows time" aren't the best phrases to use. No inertial frame is "moving" any more than another. They are all moving relative to each other.

Time dilation in its simplest form refers to the fact that if two events occur at the same location in one inertial frame then any frame moving relative to it will measure a longer time between those two events. The clocks are operating perfectly normal in each frame and time isn't slowing down in either frame. They just measure different spatial and temporal values for the events that occur.

While imprecise, I feel it conveys the idea well. To wit, to the observer in the moving spacecraft the perception of time is different. Nevertheless, I appreciate the amplification. I'm just a lay observer of the topic after all, and I accept the limits of my knowledge. Cheers

 

[Sweater of AV]

While imprecise, I feel it conveys the idea well. To wit, to the observer in the moving spacecraft the perception of time is different. Nevertheless, I appreciate the amplification. I'm just a lay observer of the topic after all, and I accept the limits of my knowledge. Cheers

Sorry to reply again but that's still problematic because there's no difference in what their perception of time is. They make measurements in the exact same way and everything seems completely normal in their respective frames. The space-time measurement outcomes for events are just different.

No worries though. Those statements can maybe be helpful in getting someone interested in the subject but they have to be abandoned pretty quickly, especially once you start transforming quantities between different reference frames. Anyways, I didn't really want to respond in the first place but I felt like those statements might confuse people like TS. Cheers.

 

[Takes_Two_To_Tango]

Here some great quotes about 'Time'.

"Time is an illusion." - Albert Einstein

"If time travel is possible, where are the tourists from the future?" - Stephen Hawking

"Yesterday’s the past, tomorrow’s the future, but today is a gift. That’s why it’s called the present." - Bil Keane

"Change your 24 hours and you will change your life." - Eric Thomas

"If we take care of the moments, the years will take care of themselves." - Maria Edgeworth

 

[Andy Capp]

Here some great quotes about 'Time'.

"Time is an illusion." - Albert Einstein

"If time travel is possible, where are the tourists from the future?" - Stephen Hawking

"Yesterday’s the past, tomorrow’s the future, but today is a gift. That’s why it’s called the present." - Bil Keane

"Change your 24 hours and you will change your life." - Eric Thomas

"If we take care of the moments, the years will take care of themselves." - Maria Edgeworth

Supplemental:

 

[Andy Capp]

Sorry to reply again but that's still problematic because there's no difference in what their perception of time is. They make measurements in the exact same way and everything seems completely normal in their respective frames. The space-time measurement outcomes for events are just different.

No worries though. Those statements can maybe be helpful in getting someone interested in the subject but they have to be abandoned pretty quickly, especially once you start transforming quantities between different reference frames. Anyways, I didn't really want to respond in the first place but I felt like those statements might confuse people like TS. Cheers.

Time dilation is for sure a complex concept. If you'd care to, please elaborate on "The space-time measurement outcomes for events are just different." and how that is different from what I said.

 

[ralphc1]

Just to point something out that creates a lot of confusion. "Moving clocks slow down" and "motion slows time" aren't the best phrases to use. No inertial frame is "moving" any more than another. They are all moving relative to each other.

Time dilation in its simplest form refers to the fact that if two events occur at the same location in one inertial frame then any frame moving relative to it will measure a longer time between those two events. The clocks are operating perfectly normal in each frame and time isn't slowing down in either frame. They just measure different spatial and temporal values for the events that occur.

Time and motion are intertwined. One doesn't exist without the other. The way to tell if something is moving requires checking it's position at different intervals of time. Time is determined by the motion of something like the sun, stars, a pendulum or the resonance frequency of atoms. All motion is relative as everything i in motion. If nothing moves there would be no time.

When we look at stars we are looking at their positions when the light escaped their gravitational field. They may no longer even exist. The light that came from them could have been diverted from it's path by gravity along the way so it can't be assumed that a star was even in the position that it appeared to be in.

 

[Batjester]

I'm not even close to high enough for this conversation.

 

[Sweater of AV]

Time and motion are intertwined. One doesn't exist without the other. The way to tell if something is moving requires checking it's position at different intervals of time. Time is determined by the motion of something like the sun, stars, a pendulum or the resonance frequency of atoms. All motion is relative as everything i in motion. If nothing moves there would be no time.

When we look at stars we are looking at their positions when the light escaped their gravitational field. They may no longer even exist. The light that came from them could have been diverted from it's path by gravity along the way so it can't be assumed that a star was even in the position that it appeared to be in.

Well yes this is all very straightforward but for some reason you're not addressing the actual point.

Your statement "motion slows time" is not correct. The frames are moving relative to each other. If frame A is moving at +v with respect to frame B then frame B is moving at -v with respect to A. Nothing is "slowed" because of motion. Whatever is being used as a clock in each frame is working perfectly normal.

If you want to actually address your statement of "motion slows time" then go for it. You're not addressing it by anything you've written in that post.

 

[Jack Reacheround]

if we sent that person 5 years to the nearest star, and 5 years back...we would expect 10 years to pass for the person on earth. However, the person traveling we would expect would experience time at a slower rate. When we hear "it would take 5 years to reach the nearest start at 99% SOL, how could we say it would actually take 5 years? Because relative to the person on the ship, it should only take 1 year to reach the star, and 1 year to make it back. 2 years total. Bc remember, the person on the ship would expect would only age 2 years vs the person on each aging 10 by the time they made it back.

To the person traveling, it would be 5 years to and 5 years back.
To anyone who was observing from a relatively motionless position, it would have taken them 50 years for the round trip.

 

[Sweater of AV]

Time dilation is for sure a complex concept. If you'd care to, please elaborate on "The space-time measurement outcomes for events are just different." and how that is different from what I said.

Their measurement outcomes of position and time are different but neither has a skewed perception of time itself. The statement "To wit, to the observer in the moving spacecraft the perception of time is different" makes it seem like the way time itself is actually perceived is fundamentally different in one frame as opposed to the other, which isn't true.

 

[Andy Capp]

Their measurement outcomes of position and time are different but neither has a skewed perception of time itself. The statement "To wit, to the observer in the moving spacecraft the perception of time is different" makes it seem like the way time itself is actually perceived is fundamentally different in one frame as opposed to the other, which isn't true.

Their perception is different because their measured outcomes are different, wouldn't you say? One logically follows automatically from the other, doesn't it?

 

[moreorless87]

The best explanation I'v seen(if i understood it anyway) is that you have to think of time as a dimension you can travel though similar to space, if the X axis is space and the Y axis is time then when your not moving though space you travel directly up the Y axis of time, when your traveling at the speed of light you travel only on the X axis though space and not though time.

So light speed is the speed it is because thats the point at which time stops, were all of your movement is though space rather than time.

 

[Sweater of AV]

Their perception is different because their measured outcomes are different, wouldn't you say? One logically follows automatically from the other, doesn't it?

No, I wouldn't agree with that. I would actually separate "perception" and "scientific measurement" about as far as possible. Human perception is never really based on scientific measurements. Also, "perception of time" sounds like you're referring to how time itself as a physical entity is being perceived. That isn't fundamentally changed in either frame. I really wouldn't use the term "perception of time" here but if you want to then go nuts.

 

[Judoka1532]

Whenever you ask "how long does it take?" you have to specify the reference frame. Trying to pose the question in an absolute sense makes no sense in relativity theory. Using the numbers you've provided for the discussion, in the frame of reference of the person on Earth, it takes five years for the ship to reach the star. In the frame of reference of the person on the ship, it takes one year. That's all that can be said.

Now, if you want to directly compare time passage between clocks in two different reference frames, then you will have to bring them into the same reference frame which requires acceleration and non-inertial reference frames. That's an entirely different discussion than time dilation and inertial reference frames.

So I think if you are right you answered my question. Basically, for the person on the ship, you could travel to the nearest star (4-5 years at the speed of light timed by a person on earth) in approx 1 year?

 

[Judoka1532]

The whole issue here is changing frames of reference. Einstein proved that moving clocks slow down. He also showed that your perception of how time passes depends upon your frame of reference. That means that for the people on the spaceship travelling near the speed of light time passes more slowly than for people living on Earth, and the closer you get to the speed of light, the more slowly time passes. This has been demonstrated experimentally by comparing the difference in age of human twins, one of whom stayed on the ISS for a year or so, travelling at 17,500 mph the entire time, while his brother stayed on Earth. It was shown to be true long before that, though by just putting atomic clocks on airplanes and flying them around at high altitude.

HTH

how did they measure the difference in age between human though? I understand the clock concept though

 

[90 50]

I don’t beleive in time dilation theories.

 

[Judoka1532]

To the person traveling, it would be 5 years to and 5 years back.
To anyone who was observing from a relatively motionless position, it would have taken them 50 years for the round trip.

I don't think you are right based on the answers others have given me.

In the scenario I posed, I think the longest amount of time for any observer is going to be 10 years total. The person traveling will only age let's just say 2 years total (1 there and 1 back). 10 years for the person on earth.

I dont think it can take more than 10 years for the observer on earth. And think of it this way, if there was a big mirror on the star, we could beam a ray of light to it and back in 10 years our time. We would be measuring that. Given the light speed of the ray of light, and the light speed of the person on a ship, there is no difference in their speed. The only difference would be a biological being on that ship would age less.

And this isn't an arrogant answer from me, heck I could still be wrong. Part of why I asked the question.

 

[Andy Capp]

how did they measure the difference in age between human though? I understand the clock concept though

I could easily be wrong but I think it was via some combination of normal body cycles, things like cell death and replacement, circadian rhythms, and/or telomere shortening and the like. I expect a quick google would turn up the correct answer. I forget the guys' names but it shouldn't be too hard to pull up results for twin astronauts and aging.

 

[Sweater of AV]

So I think if you are right you answered my question. Basically, for the person on the ship, you could travel to the nearest star (4-5 years at the speed of light timed by a person on earth) in approx 1 year?

Yes, relative to the person on the ship, it takes one year. Relative to the person on Earth, it takes longer. However be careful to not say "4-5 years at the speed of light timed by a person on earth." That's not the right way of saying it. No one is traveling at the speed of light.

You can pretty easily find out the time measured by the person on Earth. If the person on the ship measures one year and the ship is traveling at 99% of the speed of light then it will take approximately 7.1 years for the ship to the reach the star as measured by the person on Earth.