Theories of Einstein

[AstroTiger]

Hi, all

At the moment i am trying to get my head around the fact that if we travelled to say M31 at 99.99999999 % of the speed of light, we would actually only age 50 odd years even though it will take 2.25 million years to get there?

So if out offpring therefore returned to earth at the same speed, taking another 50 of their years to get there they would be returning to an earth some 6 million years after their parents left.

The offspring too would be the order of 2 million years old?

Is this correct, in terms of how i have interpreted this?

[MikeP]

I think you must be right. There is an identical example on p55 of "Why Does E = mc**2".

Mike

[astro_dt]

Hi AT

By coincidence I posted a form of explanation on another forum this morning, so may as well try it here. The effect is known as time dilation and the mathematics comes from the Lorentz transformation but I want to try and paint a verbal picture.

Think first about a 2 dimensional world where your speed is limited no matter what direction you travel (North, South, East and West). The faster you travel in the N-S direction, the slower you can travel E to W and vice versa. If you drive North at top speed you cannot travel E or W.

Now extend the analogy to the three spacial dimensions we are familiar with, add time as a fourth dimension and set the speed limit to the speed of light. As you travel closer to the speed of light in the spatial dimensions, you have to travel slower in the time dimension. So time slows down as you approach the speed of light. For an observer who is relatively (no pun intended) stationary on Earth time still moves along the time dimension at what we call "normal."

Hope this helps and I don't get riped apart for over-simplifying the problem. This is just one interesting way of looking at it.

Danny

[AstroTiger]

I think the main thing to consider here is, time is relative to space.

Because time ticks at a constant rate, we set calibrate our lives by it.

The only puzzling thing though is what can matter not travel at the speed of light?

I will likely get the answer in the book you described, which coincidentally again, i happen to be reading :-)

[Space Bat]

I think the main thing to consider here is, time is relative to space.

Because time ticks at a constant rate, we set calibrate our lives by it.

The only puzzling thing though is what can matter not travel at the speed of light?

I will likely get the answer in the book you described, which coincidentally again, i happen to be reading :-)

Is light constant?? previously thought so - but now people are becoming more aware that its not....

Is time constant?? Now this is tricky to explain....

But simply you can travel faster than light - you need to travel as fast as time... to some people this is such a daft statement and will go against all their thought processes and training...

One thing is for sure at some point we will have the technology and understanding that E=mc2 will be seen for what it is...a theory.

Chris

[acey]

AstroTiger - you're quite right in your deduction (haven't checked your actual figures but I assume the time dilation is calculated correctly).

It's called the "twin paradox" and was considered by Einstein in his first relativity paper (or one of the first). The "paradox" arises if you then say that the situation ought to be symmetric for both the space traveller and the people on Earth - the latter could regard themselves as a "space ship" while it was the rocket that "stood still", so why doesn't the person in the rocket end up older than those on Earth?

Much, much work has been done on that. The simplest and usual explanation is that the rocket traveller undergoes acceleration which he/she can feel, while the people on Earth don't. And special relativity doesn't apply to cases involving acceleration (you need general relativity for that, where supposedly everything works out nicely). But as I say, huge amounts have been said about the twin paradox, as you'll see if you try googling it.

Bertrand Russell complained there were far too many popular science books about relativity - and that was in about 1921! He went on to write one himself.

[George Jones]

Much, much work has been done on that. The simplest and usual explanation is that the rocket traveller undergoes acceleration which he/she can feel, while the people on Earth don't.

Yes.

And special relativity doesn't apply to cases involving acceleration (you need general relativity for that, where supposedly everything works out nicely).

Actually, this is a myth; special relativity handles accelerations just fine.

But as I say, huge amounts have been said about the twin paradox, as you'll see if you try googling it.

In general relativity, the situation is even stranger. Then, it is possible for two twins to be together, separate, come back together again, and have different elapsed times recorded by their watches and their ages, even when both twins experience no acceleration the entire time. This can't happen with special relativity.

[nbrus]

Please feel free to point out my ignorance if I get things wrong, but based on my limited understanding of relativity I would like to say the following...

1. "Time" is a purely human concept that provides a means for describing when certain events take place. It comes in handy when working with mathematical equations (maths being another human invention).

2. Time travel may well make sense mathematically, but is a total impossibility in reality. Hence no people from the future, or alteration of history by time travellers. No paradox here.

3. The idea of time travel is based on the assumption that the speed of light is finite, and nothing can travel faster than it.

This last statement actually provides answers to explain how time travel is perceived, and without requiring any real "time travel". Imagine that at a subatomic level all matter is in motion, whether it be electrons being exchanged in a chemical reaction, or electrical signals in the brain.

As we move closer to the speed of light, these motions are slowed. If this wasn't the case, then when travelling at the speed of light, anything in motion in the same direction as this travel, would exceed the speed of light, which as we all know is impossible.

If everything slows as we get closer to the speed of light, then ageing (a chemical reaction), perception and awareness (electrical brain activity), and measured time (mechanical watch movement, or electronic watch impulses) must also slow down.

The person that is moving at speed will not notice any change, as everything around them (in their spaceship) will be affected by an equal amount. The outside observer will not be slowed, and so the passage of time relative to the traveller, will appear faster.

The above description implies that we can only ever travel forward through time, albeit at different rates dependant solely on our speed relative to that of light, and never backwards. There are no paradoxes.

This is my simplistic view of relativity ...

[Matthew.Blake]

Please feel free to point out my ignorance if I get things wrong, but based on my limited understanding of relativity I would like to say the following...

1. "Time" is a purely human concept that provides a means for describing when certain events take place. It comes in handy when working with mathematical equations (maths being another human invention).

2. Time travel may well make sense mathematically, but is a total impossibility in reality. Hence no people from the future, or alteration of history by time travellers. No paradox here.

3. The idea of time travel is based on the assumption that the speed of light is finite, and nothing can travel faster than it.

:

1) Time is real, not just a human concept

2) Some better physicists than me disagree with you

3) Since when is time travel based on that assumption?

[acey]

Actually, this is a myth; special relativity handles accelerations just fine.

Sure - I was giving the "simple" version.

[nbrus]

1) Time is real, not just a human concept

2) Some better physicists than me disagree with you

3) Since when is time travel based on that assumption?

1. How so?

2. And Jesus will return one day to save us all...

3. On what premise is time travel based?

[Matthew.Blake]

1. How so?

2. And Jesus will return one day to save us all...

3. On what premise is time travel based?

1) It can be measured

2) Disagree with them all you want, they may well be wrong - thus is the nature of science

3) The fact that space and time aren't really seperate entities

[George Jones]

3. On what premise is time travel based?

In Einstein's general relativity, spacetime is curved. Mathematically, there exist loads of curved spacetimes that contain closed timelike curves, i.e., paths that allow travel from the future to the past. For example, the deep interior of a rotating black hole contains a region that has closed timelike curves.

Are these closed timelike curves physically traversable? I think most physicists would answer "Probably not." No definitive answer to this question has been obtained, so this is currently an area of active research.

Possible views on closed timelike curves:

1. Physics needs to be radically rewritten from the ground up;

2. Permit time travel, but also invoke consistency constraints so that past and future mesh wihout paradoxes;

3. Quantum physics intervenes to prevent time travel;

4. The Boring Physics Conjecture, where we assume (until forced not to) that our particular universe is globally hyperbolic, and thus doesn't have closed timelike curves.

In the past, 4. was often assumed, but, many physicists have moved to 2. and 3. Stephen Hawking likes 3., for example, and has formulated the Chronology Protection Conjecture, "It seems that there is a Chronology Protection Agency which prevents the appearance of closed timelike curves and so makes the universe safe for historians."

The Chronology Protection Conjecture roughly states that near a spacetime region that has closed timelike curves, infinite energy densities are encountered, thus preventing (by wall-of-fire barriers) physical objects from traversing closed timelike curves. There seems to be some theoretical evidence for this conjecture, but other theoretical considerations indicate that a definitive answer to the question requires a quantum theory of gravity.

Matt Visser has written an interesting technical article, "The Quantum Physics of Chronology Protection," on this.

[Space Bat]

1) It can be measured

Only from our perspective - we still can't quanitfy time.

2) Disagree with them all you want, they may well be wrong - thus is the nature of science

It is indeed

3) The fact that space and time aren't really seperate entities

Space can not exist without time to exist in

I would argue that Time is the biggest hole in mans understanding of the universe...If we understood it fully I dare say it can be manipulated....

Some on this forum - will believe in the possibility of UFO's and ET life and that they have visited us (personally on the fence) but if this is the case then these species have an understanding of time and how to manipulate it to travel the universe in a sensible framework to make it interesting and doable..

[Matthew.Blake]

Space cannot exist without time to exist inQUOTE]

Space and time are part of the same thing, one doesn't exist within the other. Saying space cannot exist without time to exist in is like saying the y-axis of my graph cannot exist without the x-axis of my graph to exist in.

[Space Bat]

Space cannot exist without time to exist inQUOTE]

Space and time are part of the same thing, one doesn't exist within the other. Saying space cannot exist without time to exist in is like saying the y-axis of my graph cannot exist without the x-axis of my graph to exist in.

Just a different way of agreeing with you Matthew

[nbrus]

"Space cannot exist without Time"

How about..."Speed cannot exist without distance"...

These are simply mathematical constructs used to describe behaviour, measurements, or physical properties of "real" objects. If I said "2 cm" represents a distance ... this means absolutely nothing. If I said that the diameter of my watch face is "2 cm" ... I have put this measurement in context which now has meaning.

Time and Space (a composite of 3 distances) are simply measurements, or descriptors, and not "real" physical, or even imaginary, objects. They don't exist. "Red" does not exist, it is simply a name/description for a colour.

A short example on time travel...

Imagine an observer on the ground ... his friend leaves in a rocket ship, then returns one hour later. To the observer exactly one hour has passed, but his friend has experience only 59 minutes of elapsed time.

Is this a case of time travel? Consider the following...

Both observer and his friend are currently face to face in the 'present'.

If time had really passed more slowly in the space ship, then relative to his observer, the space traveller would not exist in the same time as the observer, who effectively exists in the future (relative to the traveller), as time moves faster for them.

How then can someone in the present, or future relative to the traveller (observer), meet face to face with someone from the past (traveller)?

Could the answer be that the motion of all things moving at speed (including measurement devices such as clocks) effectively slow down, and that this does not represent time travel. This is a purely physical change that impersonates time travel, but time is a mathematical construct/measurement and is not a "real" thing, so no time travel ever takes place ... except maybe in Hollywood movies.

[Matthew.Blake]

"Space cannot exist without Time"

How about..."Speed cannot exist without distance"...

These are simply mathematical constructs used to describe behaviour, measurements, or physical properties of "real" objects. If I said "2 cm" represents a distance ... this means absolutely nothing. If I said that the diameter of my watch face is "2 cm" ... I have put this measurement in context which now has meaning.

Time and Space (a composite of 3 distances) are simply measurements, or descriptors, and not "real" physical, or even imaginary, objects. They don't exist. "Red" does not exist, it is simply a name/description for a colour.

A short example on time travel...

Imagine an observer on the ground ... his friend leaves in a rocket ship, then returns one hour later. To the observer exactly one hour has passed, but his friend has experience only 59 minutes of elapsed time.

Is this a case of time travel? Consider the following...

Both observer and his friend are currently face to face in the 'present'.

If time had really passed more slowly in the space ship, then relative to his observer, the space traveller would not exist in the same time as the observer, who effectively exists in the future (relative to the traveller), as time moves faster for them.

How then can someone in the present, or future relative to the traveller (observer), meet face to face with someone from the past (traveller)?

Could the answer be that the motion of all things moving at speed (including measurement devices such as clocks) effectively slow down, and that this does not represent time travel. This is a purely physical change that impersonates time travel, but time is a mathematical construct/measurement and is not a "real" thing, so no time travel ever takes place ... except maybe in Hollywood movies.

I believe your conceptual difficulty comes from either not accepting that space and time are part of the same thing (as you know imaginatively called space-time) or you are hanging on to the concept of absolute space and absolute time (i.e. there is some point that could be called the origin). It is entirely natural to do so as this is very consistent with our experience, however, when asking questions like "is time travel possible" and "is time real" our experience is unfortunately holding us back.

[nbrus]

I believe your conceptual difficulty comes from either not accepting that space and time are part of the same thing (as you know imaginatively called space-time) or you are hanging on to the concept of absolute space and absolute time (i.e. there is some point that could be called the origin). It is entirely natural to do so as this is very consistent with our experience, however, when asking questions like "is time travel possible" and "is time real" our experience is unfortunately holding us back.

You used the word 'concept' ... I can agree with that ... I am not a physicist, but I do find physics interesting. Are you able to explain why space-time is real? A tricky subject I know, but makes for interesting discussion.

[Space Bat]

Space and time are one and the same - what people find difficult is their own perceived experience of time in their own format within Spacetime

What I mean by format is how individual brains of species recognise periods of elapsed time hence dog years....etc.

For example if I were a mayfly what seems like such a brief life - could be seen as such a long one to the mayfly in what it has to accomplish for a fulfilling life.

Man as a species was given an allotted time frame to which to accomplish things such as growth, to a period of fertility and the time required to raise offspring - in effect once all possibilities of providing renewed life from our genetic code has been exhausted...and we have developed our young to go off and re-start this process - in effect we serve no purpose and should die.

Now I have put in the above not to raise philosophical debate – but to bring the notion of how species deal with the realities of purpose and how it relates to the time allowed and how time perception works within the time frame of individual existence.

All this is totally removed from what Spacetime is as it is the fundamental mechanics of how the universe works or even exists and how it progresses.

Physicist can only come up with so much information from the observable data and tools that are in our possession. So can only offer theory to most of the holes in understanding and some theories have evidence to suggest that elements of some theories can be proven?

However just as you can observe or theorise an event and offer information and evidence to demonstrate some facts to suggest theory becomes reality – it doesn’t mean that always the subject can be closed as fact.

For example stand right in front of an elephants flank only 5mm away with your nose bent against it you can offer information on what you are observing and touch feel and prod and put a lot of evidence to provide a picture of what you believe is in front of you – it won’t be the same picture of what you see 5m away…

I think when Physicist let go of Light being anyway involved in the make up of how space and time works the better – as it is a red herring for me – Light is just a part of an electromagnetic spectrum of radiation being emitted by a source.

Yes light travels in a vacuum and yes that is its speed – so what? Doesn’t mean it should be used as a yardstick for calculating the how’s and what’s of the universe does it?

So you can travel the speed of light – then time stops??? Err light seems to do just fine travelling at that speed and it seems to get to our telescopes in such an easy manner without the burden of taking an infinite time to get here…so why a rule needs to exist to try and explain why photons because of its mass can get away with it without being encumbered is beyond me…

The answer is if you can travel at the speed of time then time stops….and we don’t know how fast time is do we…? Which probably helps to explain why some data suggest things are moving away or accelerating faster than light…because it is still going somewhat slower than time..

For me personally it explains why black holes are not black - but the output of such an object isn't observable in our time... I hope to see in my lifetime what I have termed a Gamma Bomb...where a Black hole has resurfaced in our time as a massive explosion where so much mass has fallen onto the black hole which is tunneling backwards in time due to its gravitaional velocity that it explodes in a point in time and space where it can be observed...hopefully not to close and not until I am very old where the outcome would have no effect on me..thus allowing redistribution of matter to be coalesced back into stars - galaxies..etc.

OK all the above is the rantings of a mad man - so forgive me

Chris

[nbrus]

Space and time are one and the same

OK all the above is the rantings of a mad man - so forgive me

Chris

Rantings, whether mad or not, are good ... ... they give us more avenues to explore and provide thought for new ideas ... ;) ... you have to be a little mad to spend time in the cold and dark, with a towel over your head, looking down a telescope eyepiece.

[themos]

So you can travel the speed of light – then time stops???

yup.

[themos]

I think when Physicist let go of Light being anyway involved in the make up of how space and time works the better

They have. The photon just happens to be the only massless particle that we can easily observe (the gluons are all tied up in massive stuff). All massless particles would behave the same way.

[Space Bat]

yup.

Nothing wrong with classical thinking