relativity and stuff
IamSmooth, Fri Jun 30 2006, 07:56PMI am reading the book SpaceTime and I have some questions for those that think they can answer in a coherent manner. It is not that I don't understand (well, some things I don't), but I am hoping I can get a clearer answer.
For example, if light does not escape from a black hole, does the photon actually stop moving and hence the speed of light at the horizon is zero or does the wavelength just expand to a frequency of zero? If the latter, does the photon keep moving forward?
Another question: if one is holding a mirror in front of himself and is running at the speed of light does the reflection disappear or again does the wavelength shift?
Re: relativity and stuff
Marko, Fri Jun 30 2006, 08:15PM
Actually EM wave falling into a hole increases it's frequency (but speed is unchanged), until it hits the horizon and gets ultimately added to black hole's mass.
See gravitational red and blue shift:
Gravitational time dilation counters this so we can't see frequency change if we are riding the photon (but it can be seen from a distance for example).
You can imagine a bunch of things 'going wrong' when you reach speed of light, time is stopped, your mass is infinite, so the mirror thing could be imagined rather artistic.
Wavelength of light in front of you would be 'infinite' ,as your speed is equal to c, your mass is infinite and you have stopped the time (things that are pretty impossible in our plane of existence).
Conbining all that I guess you won't be able to see anything in the mirror...
Marko, Fri Jun 30 2006, 08:15PM
For example, if light does not escape from a black hole, does the photon actually stop moving and hence the speed of light at the horizon is zero or does the wavelength just expand to a frequency of zero? If the latter, does the photon keep moving forward?
Actually EM wave falling into a hole increases it's frequency (but speed is unchanged), until it hits the horizon and gets ultimately added to black hole's mass.
See gravitational red and blue shift:
Gravitational time dilation counters this so we can't see frequency change if we are riding the photon (but it can be seen from a distance for example).
Another question: if one is holding a mirror in front of himself and is running at the speed of light does the reflection disappear or again does the wavelength shift?
You can imagine a bunch of things 'going wrong' when you reach speed of light, time is stopped, your mass is infinite, so the mirror thing could be imagined rather artistic.
Wavelength of light in front of you would be 'infinite' ,as your speed is equal to c, your mass is infinite and you have stopped the time (things that are pretty impossible in our plane of existence).
Conbining all that I guess you won't be able to see anything in the mirror...
Re: relativity and stuff
Coyote Wilde, Fri Jun 30 2006, 08:49PM
The speed of light in and around a black hole is always 3*10^8 m/s, same as everywhere else (barring density issues, and rounding up.) So what happens? Look at it with from the particle perspective; ballistic trajectory, decayed orbits , that stuff. And yes, or so the theory goes, there is going to be a 'light sphere' just in or around the event horizon, where space curves such that the photons have a stable orbit around the black hole.
For the second question, you can't go at the speed of light... so let's imagine you're holding the mirror in front of you, and going at .99999999c. So, does the wavelenth shift? Nope. You and the mirror are in the same frame of reference, so your reflection will appear AS NORMAL. Behind you, on the other hand... redshift galore, and all the other fun optical abberations expected from such speeds.
Coyote Wilde, Fri Jun 30 2006, 08:49PM
The speed of light in and around a black hole is always 3*10^8 m/s, same as everywhere else (barring density issues, and rounding up.) So what happens? Look at it with from the particle perspective; ballistic trajectory, decayed orbits , that stuff. And yes, or so the theory goes, there is going to be a 'light sphere' just in or around the event horizon, where space curves such that the photons have a stable orbit around the black hole.
For the second question, you can't go at the speed of light... so let's imagine you're holding the mirror in front of you, and going at .99999999c. So, does the wavelenth shift? Nope. You and the mirror are in the same frame of reference, so your reflection will appear AS NORMAL. Behind you, on the other hand... redshift galore, and all the other fun optical abberations expected from such speeds.
Re: relativity and stuff
Carbon_Rod, Sat Jul 01 2006, 01:14AM
Black hole theories upset many people’s notions – personally I think Hawking’s theories may show some odd correlations and contradictions. However in classic terms the entire earth could only form a theoretical black hole with a radius of about 8.86mm as R=(2GM)/c^2.
In terms of Einstein’s ideas, the classic light clock problem may be illuminating.
Ultimately people like to hang on to traditional models even if they may be subject to deemphasis in mainstream theoretical sciences.
Cheers,
Carbon_Rod, Sat Jul 01 2006, 01:14AM
Black hole theories upset many people’s notions – personally I think Hawking’s theories may show some odd correlations and contradictions. However in classic terms the entire earth could only form a theoretical black hole with a radius of about 8.86mm as R=(2GM)/c^2.
In terms of Einstein’s ideas, the classic light clock problem may be illuminating.
Ultimately people like to hang on to traditional models even if they may be subject to deemphasis in mainstream theoretical sciences.
Cheers,
Re: relativity and stuff
WaveRider, Sat Jul 01 2006, 01:54PM
One of those contradictions, elucidated by Stephen Hawking, is that black holes not only absorb matter and radiation, but emit radiation and matter as well. If I remember correctly, there are two mechanisms at work....
I love studying modern physics, but unfortunately many of the papers that I've seen in the modern literature are heavy on arcane mathematical treatment and light on understanding... Or maybe I'm just a bit slow and fossilized!
WaveRider, Sat Jul 01 2006, 01:54PM
One of those contradictions, elucidated by Stephen Hawking, is that black holes not only absorb matter and radiation, but emit radiation and matter as well. If I remember correctly, there are two mechanisms at work....
1. Blackbody radiation. The black hole has a "temperature" and emits radiation characteristic of blackbody radiation. In the coordinate frame near the event horizon, the photon could look like a gamma ray, but by the time it "climbs" out of the BH gravitational well, it is redshifted into the IR of mm-wave band. Hence, the BH, over time, will lose mass and "evaporate" when it falls below its critical mass. There's no escaping the Second Law of Thermodynamics! ;)
2. Virtual particle/antiparticle pair generation. Near the event horizon, particle/antiparticle pairs can be spontaneously generated. One is swallowed up by the BH and the other is ejected into some type of orbit around the BH.
I love studying modern physics, but unfortunately many of the papers that I've seen in the modern literature are heavy on arcane mathematical treatment and light on understanding... Or maybe I'm just a bit slow and fossilized!
wrote ...
Another question: if one is holding a mirror in front of himself and is running at the speed of light does the reflection disappear or again does the wavelength shift?
You will see no change in your reflection if you are running along a line that passes through you and the mirror, because for you and the mirror, light always travels at speed c. And you will never be able to reach speed c.Another question: if one is holding a mirror in front of himself and is running at the speed of light does the reflection disappear or again does the wavelength shift?
Re: relativity and stuff
cbfull, Sat Jul 01 2006, 04:55PM
Einstein's theories have always tended to bug the hell out of me. I personally feel he used way too much mathematics to understand the universe.
Take a look at flux theory of the universe and see what you think
cbfull, Sat Jul 01 2006, 04:55PM
Einstein's theories have always tended to bug the hell out of me. I personally feel he used way too much mathematics to understand the universe.
Take a look at flux theory of the universe and see what you think
Re: relativity and stuff
Bored Chemist, Sat Jul 01 2006, 09:10PM
He gets to the end of the first paragraph before saying something completely wrong.
"if we couldn't see vibrations of electron energy, the moon would be completely unnoticed. "
What? no tides?
I stopped reading there.
Bored Chemist, Sat Jul 01 2006, 09:10PM
He gets to the end of the first paragraph before saying something completely wrong.
"if we couldn't see vibrations of electron energy, the moon would be completely unnoticed. "
What? no tides?
I stopped reading there.
Re: relativity and stuff
Steve Conner, Sat Jul 01 2006, 10:38PM
I think his head got stuffed with an infinite sized loaf that left no room for brains.
I'm wary of any theory that tries to describe the fundamental structure of the universe in terms of everyday objects like loaves of bread and dodecahedrons. Everyday objects exist entirely inside the structure of the universe, so you can't make a theory of the structure of the universe out of them, any more than you can make pi by adding integers together, or make the Haynes manual for your car out of the parts of your car.
A good theory of the universe would have to be made out of something finer and more abstract than material objects. Einstein made his theory of relativity out of thought experiments, and pure thought is pretty fine stuff. You don't need any mathematics at all to understand it though: all you need to take on board is that the speed of light always measures the same no matter where you are or how fast you're travelling.
Steve Conner, Sat Jul 01 2006, 10:38PM
gravityboy wrote ...
The Raisin bread model of expansion is also a farce, it can't expand because if the universe were a loaf, it would have to be an infinite sized loaf, or an infinite amount of loaves with no room left to expand.
The Raisin bread model of expansion is also a farce, it can't expand because if the universe were a loaf, it would have to be an infinite sized loaf, or an infinite amount of loaves with no room left to expand.
I think his head got stuffed with an infinite sized loaf that left no room for brains.
I'm wary of any theory that tries to describe the fundamental structure of the universe in terms of everyday objects like loaves of bread and dodecahedrons. Everyday objects exist entirely inside the structure of the universe, so you can't make a theory of the structure of the universe out of them, any more than you can make pi by adding integers together, or make the Haynes manual for your car out of the parts of your car.
A good theory of the universe would have to be made out of something finer and more abstract than material objects. Einstein made his theory of relativity out of thought experiments, and pure thought is pretty fine stuff. You don't need any mathematics at all to understand it though: all you need to take on board is that the speed of light always measures the same no matter where you are or how fast you're travelling.
Re: relativity and stuff
HV Enthusiast, Sat Jul 01 2006, 11:03PM
So if the universe doubled in size overnight, would there be any way we could tell??
HV Enthusiast, Sat Jul 01 2006, 11:03PM
So if the universe doubled in size overnight, would there be any way we could tell??
Re: relativity and stuff
Marko, Sat Jul 01 2006, 11:09PM
What do you mean as 'size' of universe?
Marko, Sat Jul 01 2006, 11:09PM
So if the universe doubled in size overnight, would there be any way we could tell??
What do you mean as 'size' of universe?
Re: relativity and stuff
HV Enthusiast, Sun Jul 02 2006, 01:00AM
I mean if everything doubled in size over night.
Would you know?
HV Enthusiast, Sun Jul 02 2006, 01:00AM
I mean if everything doubled in size over night.
Would you know?
Re: relativity and stuff
Chris Russell, Sun Jul 02 2006, 01:28AM
Well, size is relative, too. Relative to some fixed measurement. In order for your question to make sense, you'll have to indicate some fixed measurement that did not also "double in size." Otherwise the question is meaningless, equivalent to asking "if all time stopped for a billion years, freezing everything in the universe, and then started again, would we know?"
Chris Russell, Sun Jul 02 2006, 01:28AM
Well, size is relative, too. Relative to some fixed measurement. In order for your question to make sense, you'll have to indicate some fixed measurement that did not also "double in size." Otherwise the question is meaningless, equivalent to asking "if all time stopped for a billion years, freezing everything in the universe, and then started again, would we know?"
Re: relativity and stuff
ragnar, Sun Jul 02 2006, 01:30AM
I suppose if the universe was only one day old, then light travelled for another day... wait a second.. what?
Ah, redshifting and notable change of intergalactic distances?
ragnar, Sun Jul 02 2006, 01:30AM
I suppose if the universe was only one day old, then light travelled for another day... wait a second.. what?
Ah, redshifting and notable change of intergalactic distances?
Re: relativity and stuff
HV Enthusiast, Sun Jul 02 2006, 03:12AM
The question, is, "if the universe doubled in size overnight, how would you tell?"
Although this question may seem meaningless on the outside, its one of the most classic questions presented on the topic.
Geesh, i remember we spent two weeks worth of lectures debating this single question in an advanced physics course back in my college days . . .
HV Enthusiast, Sun Jul 02 2006, 03:12AM
The question, is, "if the universe doubled in size overnight, how would you tell?"
Although this question may seem meaningless on the outside, its one of the most classic questions presented on the topic.
Geesh, i remember we spent two weeks worth of lectures debating this single question in an advanced physics course back in my college days . . .
Re: relativity and stuff
Carbon_Rod, Sun Jul 02 2006, 05:26AM
"I mean if everything doubled in size over night. Would you know?"
If you are referring to homogeneity in space would imply a conservation of energy -- then yes it could be evident.
Carbon_Rod, Sun Jul 02 2006, 05:26AM
"I mean if everything doubled in size over night. Would you know?"
If you are referring to homogeneity in space would imply a conservation of energy -- then yes it could be evident.
Re: relativity and stuff
Steve Conner, Sun Jul 02 2006, 09:58AM
If nothing can travel faster than light, then it's just not possible for the universe to double in size overnight, because it's too big. (We measure distances between stars in light-years.) So the question is meaningless and you shouldn't expect to be able to find an answer.
Steve Conner, Sun Jul 02 2006, 09:58AM
If nothing can travel faster than light, then it's just not possible for the universe to double in size overnight, because it's too big. (We measure distances between stars in light-years.) So the question is meaningless and you shouldn't expect to be able to find an answer.
Re: relativity and stuff
HV Enthusiast, Sun Jul 02 2006, 12:36PM
Ah, so if nothing can travel faster than light, how do you explain the big bang. The universe went from practically a singularity to an entire universe in under a microsecond.
So again, I ask, if a similar process took place, hypothetically of course, and the space expanded by a factor of 2 (i.e. doubled in size) overnight, is there anyway you could tell it had occurred ? ? ?
HV Enthusiast, Sun Jul 02 2006, 12:36PM
Steve Conner wrote ...
If nothing can travel faster than light, then it's just not possible for the universe to double in size overnight, because it's too big. (We measure distances between stars in light-years.) So the question is meaningless and you shouldn't expect to be able to find an answer.
If nothing can travel faster than light, then it's just not possible for the universe to double in size overnight, because it's too big. (We measure distances between stars in light-years.) So the question is meaningless and you shouldn't expect to be able to find an answer.
Ah, so if nothing can travel faster than light, how do you explain the big bang. The universe went from practically a singularity to an entire universe in under a microsecond.
So again, I ask, if a similar process took place, hypothetically of course, and the space expanded by a factor of 2 (i.e. doubled in size) overnight, is there anyway you could tell it had occurred ? ? ?
Re: relativity and stuff
Marko, Sun Jul 02 2006, 12:47PM
Universe was *much* smaller during inflation than today, but expansion took some incredibly small amount of time.
Mechanism is a bit more complicated but nothing ever gone nor will be going by speed of light or more. Inflation was driven by expansion of 'space' itself, and insinde it nothing actually moved at speed of light.
I just figured out that your question was osmething like 'if we could repeat inflation in our universe today, and double it's size, what would happen'?
From our point I think nothing would be visible to us, if thinking of it like big-bang inflation thing.
Marko, Sun Jul 02 2006, 12:47PM
Ah, so if nothing can travel faster than light, how do you explain the big bang. The universe went from practically a singularity to an entire universe in under a microsecond.
Universe was *much* smaller during inflation than today, but expansion took some incredibly small amount of time.
Mechanism is a bit more complicated but nothing ever gone nor will be going by speed of light or more. Inflation was driven by expansion of 'space' itself, and insinde it nothing actually moved at speed of light.
I just figured out that your question was osmething like 'if we could repeat inflation in our universe today, and double it's size, what would happen'?
From our point I think nothing would be visible to us, if thinking of it like big-bang inflation thing.
Re: relativity and stuff
cbfull, Sun Jul 02 2006, 03:32PM
I agree that the flux theory website I linked to is not without it's flaws, but it's more the concept that I am after.
I personally believe that everything in the universe is made out of sub-dimensional wavelengths/waveshapes. With this theory, there is a much simpler explanation for just about everything in the universe. The reference to a dodecahedron as a model for what space is filled with is nothing new. It's a concept for visualization, not a real thing.
I think that guys site could use a lot of work, but the basic concepts are worth reading through. His explanation for the force of gravity is very sloppy, and doesn't really seem to explain anything.
cbfull, Sun Jul 02 2006, 03:32PM
I agree that the flux theory website I linked to is not without it's flaws, but it's more the concept that I am after.
I personally believe that everything in the universe is made out of sub-dimensional wavelengths/waveshapes. With this theory, there is a much simpler explanation for just about everything in the universe. The reference to a dodecahedron as a model for what space is filled with is nothing new. It's a concept for visualization, not a real thing.
I think that guys site could use a lot of work, but the basic concepts are worth reading through. His explanation for the force of gravity is very sloppy, and doesn't really seem to explain anything.
Re: relativity and stuff
HV Enthusiast, Sun Jul 02 2006, 05:54PM
I still vote that we are just in giant snow globe owned by some autistic child. Just like that show St. Elsewhere . . .
HV Enthusiast, Sun Jul 02 2006, 05:54PM
I still vote that we are just in giant snow globe owned by some autistic child. Just like that show St. Elsewhere . . .
Re: relativity and stuff
Cesiumsponge, Sun Jul 02 2006, 07:05PM
You are referring to the cosmic inflation where the universe expanded 10^50 in volume in 10^-32 seconds. Prediction models of Grand Unified Theory states that electromagnetism and the electrostrong/weak forces can be combined further into a "superforce" that would only exist under extreme energy levels of 10^15 GeV and temperatures of 10^28K+.
Obviously at those incredible densities and temperatures present at the birth of the universe (in which basic subatomic struture didn't even exist ), the speed of light by way of thought experiment would be much slower than the constant we commonly use with respect to a pure vacuum today because it took place 10^-35s after the Big Bang. It is, afterall, travelling through a mind-boggling dense medium.
That is not hospitable environment. Heck, the universe was even completely opaque to electromagnetic radiation for a long span of time. We can only check background microwave radiation back to the point where the universe was approximately 1500 times smaller than it is today, and several hundred thousand years old after the epoch of decoupling allowed the transmission of electromagnetic radiation. The universe is still expanding and the inflationary epoch did not bring the universe anywhere near it's current size as it stands today.
Describing the actual mechanics and physics (as we understand them with current knowledge) involves fun exotic stuff like high-energy false vacuums and oddball things I do not pretend to be an expert at but it was briefly covered in basic 100 and 200 level astronomy courses, and likely described in detail at higher levels. I am not sure if theories have changed since the last four years as astronomy theory and knowledge seems to change with more regularity than other branches of science.
Cesiumsponge, Sun Jul 02 2006, 07:05PM
EastVoltResearch wrote ...
Ah, so if nothing can travel faster than light, how do you explain the big bang. The universe went from practically a singularity to an entire universe in under a microsecond.
Ah, so if nothing can travel faster than light, how do you explain the big bang. The universe went from practically a singularity to an entire universe in under a microsecond.
You are referring to the cosmic inflation where the universe expanded 10^50 in volume in 10^-32 seconds. Prediction models of Grand Unified Theory states that electromagnetism and the electrostrong/weak forces can be combined further into a "superforce" that would only exist under extreme energy levels of 10^15 GeV and temperatures of 10^28K+.
Obviously at those incredible densities and temperatures present at the birth of the universe (in which basic subatomic struture didn't even exist ), the speed of light by way of thought experiment would be much slower than the constant we commonly use with respect to a pure vacuum today because it took place 10^-35s after the Big Bang. It is, afterall, travelling through a mind-boggling dense medium.
That is not hospitable environment. Heck, the universe was even completely opaque to electromagnetic radiation for a long span of time. We can only check background microwave radiation back to the point where the universe was approximately 1500 times smaller than it is today, and several hundred thousand years old after the epoch of decoupling allowed the transmission of electromagnetic radiation. The universe is still expanding and the inflationary epoch did not bring the universe anywhere near it's current size as it stands today.
Describing the actual mechanics and physics (as we understand them with current knowledge) involves fun exotic stuff like high-energy false vacuums and oddball things I do not pretend to be an expert at but it was briefly covered in basic 100 and 200 level astronomy courses, and likely described in detail at higher levels. I am not sure if theories have changed since the last four years as astronomy theory and knowledge seems to change with more regularity than other branches of science.
Re: relativity and stuff
IamSmooth, Mon Jul 03 2006, 10:10PM
Since the relativity and the universe topic seems to be getting older, like the universe, here is another relativity thought topic:
In the twin paradox the returning twin is much younger than the one stationary on earth. Part of the explaination is that the returning twin changes direction; why else couldn't the twin on earth be younger instead? My question is happens if the twin in the spacecraft did not return home, but landed on the planet after getting there at close-to-light speed? That is, is he younger than the twin at home if there is no change in direction, or is his acceleration and deceleration sufficient to satisify the paradox?
IamSmooth, Mon Jul 03 2006, 10:10PM
Since the relativity and the universe topic seems to be getting older, like the universe, here is another relativity thought topic:
In the twin paradox the returning twin is much younger than the one stationary on earth. Part of the explaination is that the returning twin changes direction; why else couldn't the twin on earth be younger instead? My question is happens if the twin in the spacecraft did not return home, but landed on the planet after getting there at close-to-light speed? That is, is he younger than the twin at home if there is no change in direction, or is his acceleration and deceleration sufficient to satisify the paradox?
Re: relativity and stuff
Desmogod, Tue Jul 04 2006, 01:09AM
Change in direction has no bearing on the twins paradox.
The closer Twin 1 gets to the speed of light, then the slower time runs for him in relation to a fixed observer, Twin 2.
If twin 1 changes direction, and flies back towards twin2 at close to the speed of light, then this will just increase the disparity in age difference, it is not a neccesity for the paradox to function.
Desmogod, Tue Jul 04 2006, 01:09AM
IamSmooth wrote ...
That is, is he younger than the twin at home if there is no change in direction, or is his acceleration and deceleration sufficient to satisify the paradox?
That is, is he younger than the twin at home if there is no change in direction, or is his acceleration and deceleration sufficient to satisify the paradox?
Change in direction has no bearing on the twins paradox.
The closer Twin 1 gets to the speed of light, then the slower time runs for him in relation to a fixed observer, Twin 2.
If twin 1 changes direction, and flies back towards twin2 at close to the speed of light, then this will just increase the disparity in age difference, it is not a neccesity for the paradox to function.
Re: relativity and stuff
Bored Chemist, Tue Jul 04 2006, 04:47PM
"I personally believe that everything in the universe is made out of sub-dimensional wavelengths/waveshapes"
What on earth does that mean?
I can't help thinking that "sub dimensional" sounds like it's straight out of a sci-fi film script.
BTW, the twins paradox isn't a paradox at all. One (and only one) twin experiences the acceleration as his ship takes off.
Velocity might be relative, but acceleration isn't (or rather it might not always be)
Bored Chemist, Tue Jul 04 2006, 04:47PM
"I personally believe that everything in the universe is made out of sub-dimensional wavelengths/waveshapes"
What on earth does that mean?
I can't help thinking that "sub dimensional" sounds like it's straight out of a sci-fi film script.
BTW, the twins paradox isn't a paradox at all. One (and only one) twin experiences the acceleration as his ship takes off.
Velocity might be relative, but acceleration isn't (or rather it might not always be)
Re: relativity and stuff
Marko, Tue Jul 04 2006, 04:55PM
Paradox doesn't need to be a bunch of mutually contradictive statements, event that counters intuition (wich would imply that time is a constant) is also sometims called a paradox, even if it is actually an very real physical phenomena.
Marko, Tue Jul 04 2006, 04:55PM
Paradox doesn't need to be a bunch of mutually contradictive statements, event that counters intuition (wich would imply that time is a constant) is also sometims called a paradox, even if it is actually an very real physical phenomena.
Re: relativity and stuff
Desmogod, Wed Jul 05 2006, 01:31AM
The twins paradox is only called such because at the time of relativity, everyone had a different view on time, i.e. that it was constant. It seems pretty common sense to us now that time is relative, But explaining this to someone around the time that Einstein postulated it would have blown their mind. So it remains the Twins Paradox, if only in nomenclature.
Desmogod, Wed Jul 05 2006, 01:31AM
Bored Chemist wrote ...
BTW, the twins paradox isn't a paradox at all. One (and only one) twin experiences the acceleration as his ship takes off.
Velocity might be relative, but acceleration isn't (or rather it might not always be)
BTW, the twins paradox isn't a paradox at all. One (and only one) twin experiences the acceleration as his ship takes off.
Velocity might be relative, but acceleration isn't (or rather it might not always be)
The twins paradox is only called such because at the time of relativity, everyone had a different view on time, i.e. that it was constant. It seems pretty common sense to us now that time is relative, But explaining this to someone around the time that Einstein postulated it would have blown their mind. So it remains the Twins Paradox, if only in nomenclature.
Re: relativity and stuff
Simon, Wed Jul 05 2006, 01:57AM
Remember that velocity is relative and there is no absolute reference point in space. So how can you say that it is twin 1 who nears the speed of light and not twin 2? This question forms a true, formal paradox since despite this fact, you can definitely say that time "slows down" for twin 1.
The answer is that special relativity doesn't apply to the twins paradox as it is formulated here. Taking off from Earth and coming back again involves either a) acceleration or b) curved space time. In either case, we're entering the realm of general relativity.
While inertial reference frames are perfectly relative, acceleration is not.
Simon, Wed Jul 05 2006, 01:57AM
Desmogod wrote ...
Change in direction has no bearing on the twins paradox.
The closer Twin 1 gets to the speed of light, then the slower time runs for him in relation to a fixed observer, Twin 2.
If twin 1 changes direction, and flies back towards twin2 at close to the speed of light, then this will just increase the disparity in age difference, it is not a neccesity for the paradox to function.
Change in direction does have a place, at least in the usual formulation of the twins paradox.Change in direction has no bearing on the twins paradox.
The closer Twin 1 gets to the speed of light, then the slower time runs for him in relation to a fixed observer, Twin 2.
If twin 1 changes direction, and flies back towards twin2 at close to the speed of light, then this will just increase the disparity in age difference, it is not a neccesity for the paradox to function.
Remember that velocity is relative and there is no absolute reference point in space. So how can you say that it is twin 1 who nears the speed of light and not twin 2? This question forms a true, formal paradox since despite this fact, you can definitely say that time "slows down" for twin 1.
The answer is that special relativity doesn't apply to the twins paradox as it is formulated here. Taking off from Earth and coming back again involves either a) acceleration or b) curved space time. In either case, we're entering the realm of general relativity.
While inertial reference frames are perfectly relative, acceleration is not.
Re: relativity and stuff
Ben, Wed Jul 05 2006, 03:26PM
Nothing can travel through spacetime faster than c. Spacetime itself, aparently, has no such restrictions.
Depends on the scale(how long would it take for the information relating such changes to propagate), on the whole the universe would get colder.
Also pseudoscience is strictly forbidden.
Ben, Wed Jul 05 2006, 03:26PM
EastVoltResearch wrote ...
Ah, so if nothing can travel faster than light, how do you explain the big bang. The universe went from practically a singularity to an entire universe in under a microsecond.
Ah, so if nothing can travel faster than light, how do you explain the big bang. The universe went from practically a singularity to an entire universe in under a microsecond.
Nothing can travel through spacetime faster than c. Spacetime itself, aparently, has no such restrictions.
EastVoltResearch wrote ...
So again, I ask, if a similar process took place, hypothetically of course, and the space expanded by a factor of 2 (i.e. doubled in size) overnight, is there anyway you could tell it had occurred ? ? ?
So again, I ask, if a similar process took place, hypothetically of course, and the space expanded by a factor of 2 (i.e. doubled in size) overnight, is there anyway you could tell it had occurred ? ? ?
Depends on the scale(how long would it take for the information relating such changes to propagate), on the whole the universe would get colder.
Also pseudoscience is strictly forbidden.
Re: relativity and stuff
Bored Chemist, Wed Jul 05 2006, 05:16PM
"Remember that velocity is relative and there is no absolute reference point in space. So how can you say that it is twin 1 who nears the speed of light and not twin 2?"
Because he is the one who gets pushed back in his seat by the rocket's acceleration. The 2 twins undergo different experiences and these different experiences have different outcomes. Where's the paradox?
Granted that you don't (from common experience) expect time dilation and that therefore the different rates of aging are unexpected. That's not what the "paradox" is about.
Given that all motion is relative you can't say which twin stayed still. from that point of view a skeptic might say "How come it's the correct twin that ages; you can't say which one moved?" With no acceleration that would be a true paradox. On the other hand only one of them actually gets in the rocket and gets accelerated- that's why his time "slows down" compared to the other.
Bored Chemist, Wed Jul 05 2006, 05:16PM
"Remember that velocity is relative and there is no absolute reference point in space. So how can you say that it is twin 1 who nears the speed of light and not twin 2?"
Because he is the one who gets pushed back in his seat by the rocket's acceleration. The 2 twins undergo different experiences and these different experiences have different outcomes. Where's the paradox?
Granted that you don't (from common experience) expect time dilation and that therefore the different rates of aging are unexpected. That's not what the "paradox" is about.
Given that all motion is relative you can't say which twin stayed still. from that point of view a skeptic might say "How come it's the correct twin that ages; you can't say which one moved?" With no acceleration that would be a true paradox. On the other hand only one of them actually gets in the rocket and gets accelerated- that's why his time "slows down" compared to the other.
Re: relativity and stuff
Bjørn, Wed Jul 05 2006, 05:52PM
So what if you put twin 2 in a centrifuge with the same acceleration but with a fraction of the speed?
Bjørn, Wed Jul 05 2006, 05:52PM
So what if you put twin 2 in a centrifuge with the same acceleration but with a fraction of the speed?
Re: relativity and stuff
Bored Chemist, Thu Jul 06 2006, 04:58PM
With the same acceleration he would follow the same trajectory; acceleration is a vector quantity
The same magnitude of acceleration would be an interesting question and I guess that's what you mean.
It's an interesting question to which I don't know the answer but I guess that since the acceleration averages to zero (if he's accelerating South now then in half a revoultion's time he will be accelerating North) the time dilation will also average to zero.
Bored Chemist, Thu Jul 06 2006, 04:58PM
With the same acceleration he would follow the same trajectory; acceleration is a vector quantity
The same magnitude of acceleration would be an interesting question and I guess that's what you mean.
It's an interesting question to which I don't know the answer but I guess that since the acceleration averages to zero (if he's accelerating South now then in half a revoultion's time he will be accelerating North) the time dilation will also average to zero.
Re: relativity and stuff
Ben, Thu Jul 06 2006, 06:28PM
The time dilation does not depend on the direction, only the magnitude.
Ben, Thu Jul 06 2006, 06:28PM
Bored Chemist wrote ...
With the same acceleration he would follow the same trajectory; acceleration is a vector quantity
The same magnitude of acceleration would be an interesting question and I guess that's what you mean.
It's an interesting question to which I don't know the answer but I guess that since the acceleration averages to zero (if he's accelerating South now then in half a revoultion's time he will be accelerating North) the time dilation will also average to zero.
With the same acceleration he would follow the same trajectory; acceleration is a vector quantity
The same magnitude of acceleration would be an interesting question and I guess that's what you mean.
It's an interesting question to which I don't know the answer but I guess that since the acceleration averages to zero (if he's accelerating South now then in half a revoultion's time he will be accelerating North) the time dilation will also average to zero.
The time dilation does not depend on the direction, only the magnitude.
Re: relativity and stuff
Bored Chemist, Thu Jul 06 2006, 08:06PM
Interesting, does time slow down on a centrifuge?
Could this be a measurable effect for unstable particles decaying in a cyclotron?
Bored Chemist, Thu Jul 06 2006, 08:06PM
Interesting, does time slow down on a centrifuge?
Could this be a measurable effect for unstable particles decaying in a cyclotron?
Re: relativity and stuff
Bjørn, Thu Jul 06 2006, 09:28PM
There is a clock postulate that says that the time is unaffected by acceleration and it is supported by particle experiments. That would mean that time is affected by the relative speed change that may be a result of acceleration(s) but not affected by acceleration itself.
As I understand it the clock postulate can't be proved or disproved by special or general relativity.
Bjørn, Thu Jul 06 2006, 09:28PM
There is a clock postulate that says that the time is unaffected by acceleration and it is supported by particle experiments. That would mean that time is affected by the relative speed change that may be a result of acceleration(s) but not affected by acceleration itself.
As I understand it the clock postulate can't be proved or disproved by special or general relativity.
Re: relativity and stuff
cbfull, Thu Jul 06 2006, 09:36PM
This is my personal opinion only, so please don't flame me.
I don't believe in the twin paradox. Something tells me that we are trying to interpret reality based on visual observation, which goes completely out the window when you start talking about travelling at the speed of light.
You cannot use visual observation to determine what is really happening. You must treat the matter as though you are blind, otherwise what is observed visually will drastically complicate and confuse the matter. Who cares what things look like at these speeds, what matters is what happens when your eyes are closed. If you want to discuss bizarre visual phenomena, then that is another matter altogether, and should be treated as a visual phenomenon ONLY.
Sorry, bit of a rant.
cbfull, Thu Jul 06 2006, 09:36PM
This is my personal opinion only, so please don't flame me.
I don't believe in the twin paradox. Something tells me that we are trying to interpret reality based on visual observation, which goes completely out the window when you start talking about travelling at the speed of light.
You cannot use visual observation to determine what is really happening. You must treat the matter as though you are blind, otherwise what is observed visually will drastically complicate and confuse the matter. Who cares what things look like at these speeds, what matters is what happens when your eyes are closed. If you want to discuss bizarre visual phenomena, then that is another matter altogether, and should be treated as a visual phenomenon ONLY.
Sorry, bit of a rant.
Re: relativity and stuff
Chris Russell, Thu Jul 06 2006, 10:14PM
So what you're really saying is that we can't use direct observation, or "too much mathematics" to understand the universe?
Chris Russell, Thu Jul 06 2006, 10:14PM
So what you're really saying is that we can't use direct observation, or "too much mathematics" to understand the universe?
Re: relativity and stuff
Carbon_Rod, Fri Jul 07 2006, 01:49AM
Numerical abstraction aside, mixing Newton and Einstein is not a good idea. You may end up overcomplicating something simple or oversimplifying something complex.
If you were alluding to the popular theoretical loophole that allows time-travel buy using a black hole? Although mathematically plausible it has nothing to do with centrifuges and does not necessarily have to be related to Kerr hole like structures (science fiction fans always like this one.)
Not to mention this thread may disappear into a black hole even if the subject was tactfully approached.
""too much mathematics" to understand the universe?"
Bah ha ha ha lol -- That’s the funniest thing I heard today... Descarte cursed many generations with the notion that a few lines on a page can plot all vector spaces. He was wrong about many things, but made numerous contributions to mathematics.
"Just because you can’t see it does not mean it isn’t there."
Carbon_Rod, Fri Jul 07 2006, 01:49AM
Numerical abstraction aside, mixing Newton and Einstein is not a good idea. You may end up overcomplicating something simple or oversimplifying something complex.
If you were alluding to the popular theoretical loophole that allows time-travel buy using a black hole? Although mathematically plausible it has nothing to do with centrifuges and does not necessarily have to be related to Kerr hole like structures (science fiction fans always like this one.)
Not to mention this thread may disappear into a black hole even if the subject was tactfully approached.
""too much mathematics" to understand the universe?"
Bah ha ha ha lol -- That’s the funniest thing I heard today... Descarte cursed many generations with the notion that a few lines on a page can plot all vector spaces. He was wrong about many things, but made numerous contributions to mathematics."Just because you can’t see it does not mean it isn’t there."
Re: relativity and stuff
Simon, Fri Jul 07 2006, 05:44AM
This is closely related to something that confused me before I studied relativity in physics. If motion is relative, how can you ever say whose time slows down in normal situations without acceleration?
Say I travel from near Earth to Jupiter at relativistic speed and Eve is watching me. We're both timing. Who measures the longer time? The key is to think about it in terms of time between events. The first event is being near Earth, the second is being at Jupiter. From my point of view, both happened at the same place (I'm still sitting in my spaceship). For Eve, one was near and one far. That's the difference.
What's the answer? Eve measures the longer time.
Simon, Fri Jul 07 2006, 05:44AM
Bored Chemist wrote ...
"Remember that velocity is relative and there is no absolute reference point in space. So how can you say that it is twin 1 who nears the speed of light and not twin 2?"
Because he is the one who gets pushed back in his seat by the rocket's acceleration. The 2 twins undergo different experiences and these different experiences have different outcomes. Where's the paradox?
BC, read my post more carefully and you'll see that that question was rhetorical and I gave it more or less the same answer as you did. I finished it off by saying that since acceleration is significant, special relativity isn't valid."Remember that velocity is relative and there is no absolute reference point in space. So how can you say that it is twin 1 who nears the speed of light and not twin 2?"
Because he is the one who gets pushed back in his seat by the rocket's acceleration. The 2 twins undergo different experiences and these different experiences have different outcomes. Where's the paradox?
wrote ...
Given that all motion is relative you can't say which twin stayed still. from that point of view a skeptic might say "How come it's the correct twin that ages; you can't say which one moved?" With no acceleration that would be a true paradox. On the other hand only one of them actually gets in the rocket and gets accelerated- that's why his time "slows down" compared to the other.
As I said, it's an almost true answer, since it takes general relativity to see what happens to the twin who accelerates.Given that all motion is relative you can't say which twin stayed still. from that point of view a skeptic might say "How come it's the correct twin that ages; you can't say which one moved?" With no acceleration that would be a true paradox. On the other hand only one of them actually gets in the rocket and gets accelerated- that's why his time "slows down" compared to the other.
This is closely related to something that confused me before I studied relativity in physics. If motion is relative, how can you ever say whose time slows down in normal situations without acceleration?
Say I travel from near Earth to Jupiter at relativistic speed and Eve is watching me. We're both timing. Who measures the longer time? The key is to think about it in terms of time between events. The first event is being near Earth, the second is being at Jupiter. From my point of view, both happened at the same place (I'm still sitting in my spaceship). For Eve, one was near and one far. That's the difference.
What's the answer? Eve measures the longer time.
Re: relativity and stuff
Bored Chemist, Fri Jul 07 2006, 05:56AM
"I don't believe in the twin paradox. "
If you are prepared to think of 2 atomic clocks as twins then the"paradox" has been demonstrated.
One clock really does run slow.
Bored Chemist, Fri Jul 07 2006, 05:56AM
"I don't believe in the twin paradox. "
If you are prepared to think of 2 atomic clocks as twins then the"paradox" has been demonstrated.
One clock really does run slow.
Re: relativity and stuff
WaveRider, Fri Jul 07 2006, 08:58AM
Clocks also run ever-so-slightly faster on the surface of the earth than in space. For example, GPS signals must take this into account, as well as the motion of its satellites, if errors are not to accumulate over time in the timing of its signals.
The resolution of the twin paradox lies indeed in who "feels" the acceleration (i.e. jumps from one inertial frame to another).. See the "adventure of Terence and Stella."
WaveRider, Fri Jul 07 2006, 08:58AM
Clocks also run ever-so-slightly faster on the surface of the earth than in space. For example, GPS signals must take this into account, as well as the motion of its satellites, if errors are not to accumulate over time in the timing of its signals.
The resolution of the twin paradox lies indeed in who "feels" the acceleration (i.e. jumps from one inertial frame to another).. See the "adventure of Terence and Stella."
Re: relativity and stuff
Bjørn, Fri Jul 07 2006, 12:03PM
Those that have an opinion on if Einstein was confused or not should keep an eye on this page: http://einstein.stanford.edu/
Bjørn, Fri Jul 07 2006, 12:03PM
Those that have an opinion on if Einstein was confused or not should keep an eye on this page: http://einstein.stanford.edu/
Clocks also run ever-so-slightly faster on the surface of the earth than in space.When we recieve the signals from the GPS it is blueshifted because the signal is "falling" in the gravity field, so we observe time to go slower in our gravity field.
Re: relativity and stuff
WaveRider, Fri Jul 07 2006, 12:38PM
Ooops! Indeed, I stand corrected! Clocks run slower in gravitational potential wells.....
WaveRider, Fri Jul 07 2006, 12:38PM
Ooops! Indeed, I stand corrected! Clocks run slower in gravitational potential wells.....
Re: relativity and stuff
Dr. Dark Current, Sat Jul 08 2006, 11:33AM
What do you think about this? At least for me it makes sense.
J.M.
Dr. Dark Current, Sat Jul 08 2006, 11:33AM
What do you think about this? At least for me it makes sense.
J.M.
Re: relativity and stuff
Bjørn, Sat Jul 08 2006, 01:46PM
I think it contains some interesting ideas that has little root in reality. Representing these ideas as some sort of theory is not honest. It also contains some startling errors like "600 km/hr, our speed with respect to the CMBR frame, is a very high velocity" that makes me suspect that he did not read what he wrote. If he does not take it serious then there is no reason for us to take it serious.
Bjørn, Sat Jul 08 2006, 01:46PM
I think it contains some interesting ideas that has little root in reality. Representing these ideas as some sort of theory is not honest. It also contains some startling errors like "600 km/hr, our speed with respect to the CMBR frame, is a very high velocity" that makes me suspect that he did not read what he wrote. If he does not take it serious then there is no reason for us to take it serious.
Re: relativity and stuff
IamSmooth, Sat Jul 08 2006, 05:28PM
Here is another question about relativity taken from Spacetime Physics.
I assume we accept the fact that clocks run slow when moving at high speed. If we have a train moving at 0.9c relative to earth the clock on the train runs slower than the train on earth. Now lets say a man is running against the train at the speed 0.9c such that his position doesn't change with respect to the earth. His clock should run slow compared to the clock on the train.
One would think that his clock is doubly slow compared to the earth clock; however, if he is not moving with respect to the earth wouldn't his clock run at the same speed as the clock on earth?
IamSmooth, Sat Jul 08 2006, 05:28PM
Here is another question about relativity taken from Spacetime Physics.
I assume we accept the fact that clocks run slow when moving at high speed. If we have a train moving at 0.9c relative to earth the clock on the train runs slower than the train on earth. Now lets say a man is running against the train at the speed 0.9c such that his position doesn't change with respect to the earth. His clock should run slow compared to the clock on the train.
One would think that his clock is doubly slow compared to the earth clock; however, if he is not moving with respect to the earth wouldn't his clock run at the same speed as the clock on earth?
Print this page