In some frames of reference there is no limit to the speed of light?

maninasia

Here is the situation, and it is taken from a book I have been reading recently.

There is a spaceship constantly accelerating over time. It is launched from Earth, goes to a nearby star, and comes back again a few years later.

You have multiple frames of reference.

From the perspective of the observers on Earth, the time elapsed took 50-100 years. From the perspective of the astronauts on the spaceship it only took a few years.

From the perspective of observers on Earth, the spaceship never passed the maximum speed of light, it just reached very close to the maximum. However to the astronauts on the spaceship they marched right through the speed of light and kept on accelerating until they reached a peak speed and started decelerating when coming back to Earth.

Whose frame of reference is correct? Can we say that the astronauts did not pass the accepted speed of light. Their instruments told them they did. Their age tells them they did. Their physical reality tells them they did.

And if nobodies frame of reference is the only correct version it is legitimate to agree that the speed of light has no barrier in some situations.


(yes there is a caveat that you need a LOT of energy to constantly accelerate..let's put that aside for the moment)

Duff Man Jr.

Hey, as well as time changing from perspective so does distance. So while it travels 100 light years distance from earths perspective its only traveled 10 from the spaceships perspective (assuming it has sped up). It never breaks the speed of light from anyones perspective (as it has not travelled 100 light years).
They are both right (vid below).

*Numbers made up obviously

https://www.youtube.com/watch?v=wteiuxyqtoM

maninasia

Duff Man Jr. wrote: »

Hey, as well as time changing from perspective so does distance. So while it travels 100 light years distance from earths perspective its only traveled 10 from the spaceships perspective (assuming it has sped up). It never breaks the speed of light from anyones perspective (as it has not travelled 100 light years).
They are both right (vid below).

*Numbers made up obviously

https://www.youtube.com/watch?v=wteiuxyqtoM

Is distance swappable with speed here? As speed is a function of distance/time why is distance said to have contracted instead of the speed said to have been faster as time decreased and distance remained the same?

Is it just an arbitrary choice to keep people happy that the speed of light has a maximum in all frames of reference? Is it possible to definitively prove distance has shrunk instead of speed increased from the perspective of the astronaut on the spaceship?

Duff Man Jr.

maninasia wrote: »

Is distance swappable with speed here? As speed is a function of distance/time why is distance said to have contracted instead of the speed said to have been faster as time decreased and distance remained the same?

Is it just an arbitrary choice to keep people happy that the speed of light has a maximum in all frames of reference? Is it possible to definitively prove distance has shrunk instead of speed increased from the perspective of the astronaut on the spaceship?

Yes, but it involves diving into relativity and stuff which is way over my head, it's not just keeping people happy or the easy way out.

FISMA

maninasia wrote: »

From the perspective of observers on Earth, the spaceship never passed the maximum speed of light, it just reached very close to the maximum. However to the astronauts on the spaceship they marched right through the speed of light and kept on accelerating until they reached a peak speed and started decelerating when coming back to Earth.

Whose frame of reference is correct? Can we say that the astronauts did not pass the accepted speed of light. Their instruments told them they did. Their age tells them they did. Their physical reality tells them they did.

Whoever is saying that the Astronauts marched right though the speed of light is incorrect.

The speed of light is invariant. That is, the speed of light does not depend on your reference frame. c is the speed limit of our Universe.

If the astronauts are on a space ship that is whizzing by the Earth at 95% the speed of light and they turn on their head lights, no one sees the head lights going faster than the speed of light. The astronauts see the head lights come on, just as I do when I get in my car. All reference frames measure the speed of the light as c.

maninasia

Well according to the author, he says the instruments would keep on adding kms/hour and your instruments would tell you are traveling faster than the speed of light. I will do more research on this.

It's one of the chapters in this book...written by a former NASA engineer.
http://www.amazon.com/Unconventional-Flying-Objects-Scientific-Analysis/dp/1571740279

Now he may have made some error in his understanding of relativity but according to some reviewers his explanation of relativity and his maths are clear and concise.

From a reviewer

I've enjoyed every part of this very entertaining book. However I would like to mention just a couple of points, for the sake of completeness. Mr. Hill's concept of 'effective' speed is an interesting one and quite valid for CONSTANT SHIP VELOCITY. However across pages 387-388 he makes the erroneous statement that "...all physical laws properly formulated hold good in ALL REFERENCE FRAMES." in paraphrasing Einstein. This should of course read "...ALL INERTIAL FRAMES." An accelerating space ship does NOT constitute an inertial frame of reference, hence the condition that the speed of light remain invariant in all inertial frames, does not generally hold. In fact in a non-inertial frame the value of the speed of light is C`a = C*(1+(a*cos r)/(2C*C)), where C is the usual value of the speed of light in an inertial frame and C`a is the speed of light determined in an accelerating frame. If you substitute C`a for C in Equation A5-12a you get the correct expression. This only affects the accelerated portions of the spaceship's trip. I've checked the effective speed during the constant velocity coasting and it seems to be a valid proposal.

EDIT- From re-reading the book I realise I used the wrong terminology. He uses a concept which is the 'effective speed' V, which is the time experienced on board/divided by the Earth observers distance. I think it's a very valid concept in that the speed and time experienced by the astronaut are surely the most relevant factors to him/her.

He then uses the effective speed/divided by the speed of light to show the speed of the spacecraft as experienced by the the occupants on board, which obviously exceeds the speed of light. He does NOT state that light itself exceeds C and I'm not sure how the instruments would show speed passing C in this situation, maybe they don't without taking reference to the Earth observers distance.

Another crucial part is that the spaceship needs to reach speeds close to the speed of light for the huge difference between timelines of different observers to emerge. This is something that a lot of people miss in common discourse. It does not take 100 light years to reach stars a 100 light years away if you travel at speeds close to the speed of light. Instead it could take something like 10 years for the on board occupants (depending on how close to light speed you travel, if you could actually reach light speed, the on board occupant would experience the trip instantaneously!). The effective speed ratio can be of any value. As the V/C approaches unity the effective speed ratio approaches infinity. So making a trip like this and back is perfectly feasible in terms of the occupants and their lifespans.

Anyway it's all explained in the book with the maths and relativity equations to back it up. This part is really worth a read, especially if you have the maths chomps to check his reasoning.

This is also a nice little discussion piece on effects of time dilation.
http://startswithabang.com/?p=1176

eddiethornton

Are they travelling by plane or car?

If its the latter which I suspect it's not, how is this possible and why?

Please be consise.

Keggles

maninasia

What's up with your post?

Get lost from After Hours?

...

I might ask you the same question, this is the physics and chemistry forum...

Morbert

The astronauts would not travel faster than the speed of light.

Instead, what would allow them to reach distant stars in mere moments is length contraction. Their journey would grow shorter, distance wise.

Masteroid

Morbert wrote: »

The astronauts would not travel faster than the speed of light.

Instead, what would allow them to reach distant stars in mere moments is length contraction. Their journey would grow shorter, distance wise.

That's right.

In fact, Usain Bolt only has to run 99.99994 metres. That's why he keeps winning.

FISMA

maninasia wrote: »

EDIT- From re-reading the book I realise I used the wrong terminology. He uses a concept which is the 'effective speed' V, which is the time experienced on board/divided by the Earth observers distance. I think it's a very valid concept in that the speed and time experienced by the astronaut are surely the most relevant factors to him/her.

maninasia,
If you were to stand on a scale in an elevator at rest, you could read your weight. If you were accelerating upward, the scale reads more. Your weight did not, for all measurable purposes change, the problem was that you were in an accelerated reference frame.

Our brains do not like accelerated reference frames are we are often left with the distinct impression that Newton's First Law is invalid.

The scale reading, while accelerating up or down is called the apparent weight. It's not really your weight, but you're left with a very strong impression that it is.

I think this is the source of the confusion.

Also, the author appears to be using a bit from the Earth bound reference frame (distance) and a bit from the frame of reference of the ship (time). You cannot do this.

When one frame of reference is accelerated with respect to the other, you're going to have fictitious forces (like centrifugal), apparent, and effective anomalies.

On the spaceship, all appears well and they do not notice anything strange.

Have a look at this swf - it's really well done and helps with the beginning of Special Relativity.

You should also check out this all time Physics classic.

maninasia

maninasia wrote: »

What's up with your post?

Get lost from After Hours?

...

I might ask you the same question, this is the physics and chemistry forum...

Did you see the question?
'Travel by plane or car?
If's the latter, which i suspect it's not....'


What are these questions relevant to? Did you read the opening post, it is a spaceship with astronauts on board. There are no planes or cars mentioned anywhere.

What's this plane and car stuff coming from other than to make a mockery. Seriously, please explain the relevance.
I'd rather my thread didn't get distracted by this tedious stuff, you are the mod, I thought you would read the thread. If you are going to edit my posts, please explain clearly what is the relevance of the above question? This person has just jumped into the thread, asked a random question, and not explained or contributed anything of substance.

maninasia

Our brains do not like accelerated reference frames are we are often left with the distinct impression that Newton's First Law is invalid.

The scale reading, while accelerating up or down is called the apparent weight. It's not really your weight, but you're left with a very strong impression that it is.

I think this is the source of the confusion.

Also, the author appears to be using a bit from the Earth bound reference frame (distance) and a bit from the frame of reference of the ship (time). You cannot do this.

Thanks for the examples. The astronauts instruments during the trip would never show faster than light-speed, that was my error of course.

I can see that choosing different frames of reference is cheating in a physics mindset. And yet, the astronauts traveled 100 light years by round trip, shortened to 10 light years by their extreme speed during the duration of the journey and then after they arrive back to Earth and slow down to 0 speed space kind of springs back into place, looking back, the star is 50 light years away again.

So if they calculate their speed/distance after the journey is completed you COULD say they traveled faster than light in a retrograde fashion (yes thank you all for explaining the distance has actually shrunk). It's probably not good physics, but it is a notion that makes sense to the occupant of the spaceship. In terms of how that person would manage their itinerary, plan their trip, their biological aging and ability to interact with the outside world, this may make the most sense!

In terms of accepted physics he has not technically broken the
'speed of light C' barrier, but in terms of his abilities and effective experience, he has! This is without even evoking more theoretical constructs like wormholes. What I'm really getting at is that the general public's understanding of the speed of light barrier. They believe that the speed of light C is the maximum speed one could travel and therefore it causes the distance problem (in their minds) of traveling to other stars to be very much exaggerated, at least in terms of the human individual. Of course we need massive amounts of energy to achieve this, but it is not theoretical in the slightest.

Masteroid

maninasia wrote: »

Thanks for the examples. The astronauts instruments during the trip would never show faster than light-speed, that was my error of course.

I can see that choosing different frames of reference is cheating in a physics mindset. And yet, the astronauts traveled 100 light years by round trip, shortened to 10 light years by their extreme speed during the duration of the journey and then after they arrive back to Earth and slow down to 0 speed space kind of springs back into place, looking back, the star is 50 light years away again.

So if they calculate their speed/distance after the journey is completed you COULD say they traveled faster than light in a retrograde fashion (yes thank you all for explaining the distance has actually shrunk). It's probably not good physics, but it is a notion that makes sense to the occupant of the spaceship. In terms of how that person would manage their itinerary, plan their trip, their biological aging and ability to interact with the outside world, this may make the most sense!

In terms of accepted physics he has not technically broken the
'speed of light C' barrier, but in terms of his abilities and effective experience, he has! This is without even evoking more theoretical constructs like wormholes. What I'm really getting at is that the general public's understanding of the speed of light barrier. They believe that the speed of light C is the maximum speed one could travel and therefore it causes the distance problem (in their minds) of traveling to other stars to be very much exaggerated, at least in terms of the human individual. Of course we need massive amounts of energy to achieve this, but it is not theoretical in the slightest.

I do find this all very odd. What does a 'light-year' mean anyway?

A photon travels at lightspeed so shouldn't the path of the photon be even more 'length-contracted' than the hypothetical spaceship you refer to?

If a photon takes fifty years to make a 50-ly journey how can a spaceship making the journey at sub lightspeed complete its journey in 45 years?

In effect, the spaceship would overtake all the photons emitted by the star during the five years before the spaceship began its journey back to earth.

ceejay

The 50 year duration of the journey is from the perspective of someone at rest on the Earth, since the distance is 50 light years from that frame of reference.

For the photon the distance is zero since it is travelling at c, so it takes the photon literally no time to get there

That fact messes with my head really - the photon is kind of everywhere along its path all at once, or there is no path since from the photon's perspective the size of the universe is zero along its direction of travel or something?!?

Masteroid

ceejay wrote: »

The 50 year duration of the journey is from the perspective of someone at rest on the Earth, since the distance is 50 light years from that frame of reference.

For the photon the distance is zero since it is travelling at c, so it takes the photon literally no time to get there

That fact messes with my head really - the photon is kind of everywhere along its path all at once, or there is no path since from the photon's perspective the size of the universe is zero along its direction of travel or something?!?

It messes with mine too. Especially when I think of how a photon can be red-shifted almost out of existence during that zero-time period. Like the photons that comprise the CMB Radiation. They started as high energy photons but now they are very cold by comparison. Their efficacy has been reduced.

Why should that be? If a photon with energy 'e' is emitted at the velocity 'c' and that photon is absorbed 10-billion years later by an observer who measures the velocity of the photon as 'c' in his FoR, why should 'e' have changed?

If the expansion of space or motion through space has no physical effect on a photon over time and all electrons are identical, then why should the energy of the photon be dependent on when it is absorbed by any particular electron?

It is as if photons 'spill' their energy along their journey. I could see how the 'spilled' energy is what causes expansion in the first place. In order to maintain 'c' a photon must lose ballast and lacking mass it must lose energy.

It is as if photons lose momentum over time.

I guess I just can't see what is so special about photons that they are exempted from the laws of thermodynamics.

It messes with my head.

Morbert

Masteroid wrote: »

It messes with mine too. Especially when I think of how a photon can be red-shifted almost out of existence during that zero-time period. Like the photons that comprise the CMB Radiation. They started as high energy photons but now they are very cold by comparison. Their efficacy has been reduced.

Why should that be? If a photon with energy 'e' is emitted at the velocity 'c' and that photon is absorbed 10-billion years later by an observer who measures the velocity of the photon as 'c' in his FoR, why should 'e' have changed?

If the expansion of space or motion through space has no physical effect on a photon over time and all electrons are identical, then why should the energy of the photon be dependent on when it is absorbed by any particular electron?

It is as if photons 'spill' their energy along their journey. I could see how the 'spilled' energy is what causes expansion in the first place. In order to maintain 'c' a photon must lose ballast and lacking mass it must lose energy.

It is as if photons lose momentum over time.

I guess I just can't see what is so special about photons that they are exempted from the laws of thermodynamics.

It messes with my head.

The photon's energy and momentum are frame-dependent. So from the photon's frame of reference, it hasn't lost any energy.