the speed of light question

y0ssar1an22 · 19-09-2020 12:11am #1

a question that has puzzled me for a while...

1: car A and car B have a velocity towards each other of 100 kph. they are approaching each other is 200kph.

2: if car A and car B are doing the same, but at the speed of light why are they not approaching each other at (2)(speed of light)?

if the rules of physics hold for scenario 1, why not scarios 2?

is there a simple explanation here?

i dunno, maybe we just don't have an answer?

19-09-2020 12:19am

There's a different formula for relativistic objects
Newton is out the window

Feisar · 19-09-2020 12:30am

They are approaching each other at twice the speed of light. I don't get the question tbh.

Gregor Samsa · 19-09-2020 12:33am

This is exactly what led Einstein to develop the theory of relativity: imagining what it would be like to travel at the speed of light. He quickly realised the old rules (Newtonian mechanics) are an approximation that only work for objects travelling significantly below the speed of light, and the speed of light itself is not only a limit, but a universal constant.

This page explains it, and why, when you’re dealing with the relative speed of two photons, the answer is still c (the speed of light)

https://www.physicscentral.com/experiment/askaphysicist/physics-answer.cfm?uid=20130130105151

Rodney Bathgate · 19-09-2020 12:33am

What make and model of car?

Gregor Samsa · 19-09-2020 12:35am

Feisar wrote: »

They are approaching each other at twice the speed of light. I don't get the question tbh.

They’re not. There is no “twice the speed of light”. It’s a hard limit. Their relative velocity is still the speed of light.

Feisar · 19-09-2020 12:44am

Gregor Samsa wrote: »

They’re not. There is no “twice the speed of light”. It’s a hard limit. Their relative velocity is still the speed of light.

I'm no genius so please bare with me.

Lets imagine two stars are born and both start pumping out light. Surely the light will meet in the middle between them?

bobbyy gee · 19-09-2020 12:49am

your confusing yourself

https://www.space.com/15830-light-speed.html

Gregor Samsa · 19-09-2020 12:54am

There’s an interesting phenomenon called time dilation that happens the faster you travel. It’s not something you can notice at human speeds (unless you’re measuring with an incredibly accurate atomic clock), but the faster you go, the slower time goes relative to observers travelling slower than you. If you go at 90% of the speed of light, your perception and experience of time is half of a static observer. You’ll actually age half as slow as them. If you travel at the speed of light, for you, time stops, and you’re therefore bot able to observe anything in the universe. Basically at that speed, for you, nothing else exists except yourself, and time is infinite.

If you have any mass, your mass will also become infinite at the speed of light. It would therefore take an infinite amount of energy to get you there. Your length also reduces in the axis you’re travelling the faster you go. And again, the effect is infinite at the SOL.

So, if you were a solid object of any size, it would take infinite energy to get you to the speed of light, and once you got there, you’d have infinite mass, zero length, time would stop and to you the universe would cease to exist. This clearly means that it’s impossible for anything with mass to travel at the speed of light. It also shows that nothing can travel faster than light (it would take more than infinite energy to do it, which can’t exist, and you’d end up more than infinitely massive and less than zero in length - again, things that just can’t happen)

Fortunately, photons and other particles that do travel at that speed don’t have any mass, so they don’t have to worry about the physical effects.

Gregor Samsa · 19-09-2020 12:56am

Rodney Bathgate wrote: »

What make and model of car?

that Tesla Roadster that Musk launched into space.

Gregor Samsa · 19-09-2020 1:00am

Feisar wrote: »

I'm no genius so please bare with me.

Lets imagine two stars are born and both start pumping out light. Surely the light will meet in the middle between them?

Yeah, it will* But the relative velocity of photons from both stars is still just the speed of light. The equation is in the link I posted above.

*it will relative to an outside observer not travelling at the speed of light, like you or I. To the photons themselves, they won’t meet as there is no time for them, and they don’t perceive themselves as moving at all.

Feisar · 19-09-2020 1:13am

Gregor Samsa wrote: »

Yeah, it will* But the relative velocity of photons from both stars is still just the speed of light. The equation is in the link I posted above.

*it will relative to an outside observer not travelling at the speed of light, like you or I. To the photons themselves, they won’t meet as there is no time for them, and they don’t perceive themselves as moving at all.

You have damaged my fragile little mind!

19-09-2020 1:24am

y0ssar1an22 wrote: »

a question that has puzzled me for a while...

1: car A and car B have a velocity towards each other of 100 kph. they are approaching each other is 200kph.

2: if car A and car B are doing the same, but at the speed of light why are they not approaching each other at (2)(speed of light)?

if the rules of physics hold for scenario 1, why not scarios 2?

is there a simple explanation here?

i dunno, maybe we just don't have an answer?

Each cars is still only travelling at 100kph. And if they were travelling at the speed of light neither car breaks the speed of light as individual objects.

y0ssar1an22 · 19-09-2020 2:36am

bluewolf wrote: »

There's a different formula for relativistic objects
Newton is out the window

that's the exact thing i'm confused about. all those equations of newton hold true, until they dont.

you cant have it both ways surely? One must be incorrect.

does newton's physics go out the window at a certain speed?

if they are related, is there an equation that shows that?

or do we not really know? one of those known unknowns?

y0ssar1an22 · 19-09-2020 2:37am

Rodney Bathgate wrote: »

What make and model of car?

cinquecento, its lovely

y0ssar1an22 · 19-09-2020 2:56am

Gregor Samsa wrote: »

There’s an interesting phenomenon called time dilation that happens the faster you travel. It’s not something you can notice at human speeds (unless you’re measuring with an incredibly accurate atomic clock), but the faster you go, the slower time goes relative to observers travelling slower than you. If you go at 90% of the speed of light, your perception and experience of time is half of a static observer. You’ll actually age half as slow as them. If you travel at the speed of light, for you, time stops, and you’re therefore bot able to observe anything in the universe. Basically at that speed, for you, nothing else exists except yourself, and time is infinite.

If you have any mass, your mass will also become infinite at the speed of light. It would therefore take an infinite amount of energy to get you there. Your length also reduces in the axis you’re travelling the faster you go. And again, the effect is infinite at the SOL.

So, if you were a solid object of any size, it would take infinite energy to get you to the speed of light, and once you got there, you’d have infinite mass, zero length, time would stop and to you the universe would cease to exist. This clearly means that it’s impossible for anything with mass to travel at the speed of light. It also shows that nothing can travel faster than light (it would take more than infinite energy to do it, which can’t exist, and you’d end up more than infinitely massive and less than zero in length - again, things that just can’t happen)

Fortunately, photons and other particles that do travel at that speed don’t have any mass, so they don’t have to worry about the physical effects.

your perception and experience of time is half of a static observer: has that been proven, or a conjecture?

i think infinity shouldn't be allowed. it essentially means 'going that way for a long time, but we really know' so lets call it quits'.

air · 19-09-2020 3:09am

y0ssar1an22 wrote: »

that's the exact thing i'm confused about. all those equations of newton hold true, until they dont.

you cant have it both ways surely? One must be incorrect.

does newton's physics go out the window at a certain speed?

if they are related, is there an equation that shows that?

or do we not really know? one of those known unknowns?

Newton"s equations don't work af any speed if you need absolute accuracy but they are a close enough approximation of reality to remain useful for very many day to day terrestrial applications.

y0ssar1an22 · 19-09-2020 3:46am

air wrote: »

Newton"s equations don't work af any speed if you need absolute accuracy but they are a close enough approximation of reality to remain useful for very many day to day terrestrial applications.

i always thought physics was essentially 1 + 1 = 2; a physical quantifiable 'thing' that you can solve for?'

it seems, there is so many unknowns, that people are happy to go along with the that, without any proof?

19-09-2020 3:51am

They said the speed of sound could not be broken.

Dilithium crystals ftw.

jelem · 19-09-2020 3:53am

air wrote: »

Newton"s equations don't work af any speed if you need absolute accuracy but they are a close enough approximation of reality to remain useful for very many day to day terrestrial applications.

" reality" All human constructs in this thread fail to allow we percieve
mathematics as we know it as our means to answer a question.
we are looking at it as humans looking at ants and as there is no
finite mathematical balanced answer just "near" approximations
the likes of "nearest decimal point" , it can be seen that an unknown
mor advanced "entity" may be looking at us whom have the actual factual answer
which is a whole number without minute decimal approximations.
We as humans are not there yet and as the theory of space\time being "folded"
we have No solid method of actual speed measurement and only use light as a make do
until we have gained knowledge.
the human has to rely on subjective relevance from human perspective for all our
decisions and measurements for which we are constantly reminded by disaster
when approximation does not "cut it". we may go to ufo theory as a means to
explain the unexplained which we cannot figure at this time.
this thread got too deep on trying to explain to a person whom sought an answer
for something they mentally cannot picture themselves and make a request above their understanding of
the question.
"give me an answer i dont understand" is the easy means for humans to get by
with having to think "basics" for themselves.
( just bent and folded space, brushed the surface of mars ready for the expensive waste of money human trip
for which as earth is on path to end we should be spending on sustaining life and increasing speed heading out of our
dead system towards where there may be a liveable planet to relocate as human thought has after newton\fraud etc.
seemed to have become idle which may be due to political ignorance\corruption etc.).
All the thinkers and publishers "last 25-30 years" show fear and seem produce "politically correct and acceptable"
work Only. We are doomed. lol

19-09-2020 3:58am

^^^ this dead system has another 5 billion years. Be grand.

air · 19-09-2020 4:30am

y0ssar1an22 wrote: »

i always thought physics was essentially 1 + 1 = 2; a physical quantifiable 'thing' that you can solve for?'

It is in this respect, relativity is 100% accurate at present & is used in things like GPS, it wouldn't work if not adjusted for it's effects.

y0ssar1an22 wrote: »

it seems, there is so many unknowns, that people are happy to go along with the that, without any proof?

Nobody goes along with anything without proof.
Einstein developed relativity through a series of thought experiments.
Actual experiments and observations proved him to be correct & the theory was then put into practice in many technologies that are in use today.

There are infinite numbers of unknowns of course though, that's the beauty of our universe & the never ending quest for knowledge.

Overheal · 19-09-2020 5:33am

Rodney Bathgate wrote: »

What make and model of car?

A souped up reliant robin with a Mk II warp core

Cookie_Monster · 19-09-2020 5:54am

Gregor Samsa wrote: »

They’re not. There is no “twice the speed of light”. It’s a hard limit. Their relative velocity is still the speed of light.

In theory.

blinding · 19-09-2020 7:14am

y0ssar1an22 wrote: »

a question that has puzzled me for a while...

1: car A and car B have a velocity towards each other of 100 kph. they are approaching each other is 200kph.

2: if car A and car B are doing the same, but at the speed of light why are they not approaching each other at (2)(speed of light)?

if the rules of physics hold for scenario 1, why not scarios 2?

is there a simple explanation here?

i dunno, maybe we just don't have an answer?

In the Matrix of our Universe every Observer can only observe a Maximum Speed as the Speed of Light.

This is a rule of our Matrix / Universe. Other Matrix’s / Universes may have different rules.

After I have completed my sentence in this one for my High Crimes and Misdemeanours I hope to explore other Universes / Matrix’s !

Hamsterchops · 19-09-2020 7:32am

186,000 miles per second ...

Picked that up in school many moons ago.

Rodney Bathgate · 19-09-2020 8:04am

y0ssar1an22 wrote: »

cinquecento, its lovely

Schumacher Edition?

Wanderer78 · 19-09-2020 8:09am

y0ssar1an22 wrote:

a question that has puzzled me for a while...

You're doing the wrong type of drugs for you, you need to find one or ten that relax your mind....

arctictree · 19-09-2020 8:32am

A weird effect of relativity is that for a photon of light, time stops. So from it's point of view, it can traverse the whole universe instantly.

Wanderer78 · 19-09-2020 8:33am

arctictree wrote:

A weird effect of relativity is that for a photon of light, time stops. So from it's point of view, it can traverse the whole universe instantly.

This stuff always fascinated me, but by fcuk is it a mind bender, physics is weird!

Gregor Samsa · 19-09-2020 9:15am

Cookie_Monster wrote: »

In theory.

Well, it’s a pretty solid theory, backed up by a massive amount of proof, observation and experimentation. The main issue with faster than light travel is that it would violate causality: things would happen before the thing that’s caused it.

There are theories that propose hypothetical faster then light particles called Tachyons, but all are problematic.

Chancer3001 · 19-09-2020 9:28am

What we see is only light hitting our eyes.

So when we look at a distant planet we only see what light it emitted many many years ago for example.

If i start travelling towards that planet , does what i can see speed up?

Gregor Samsa · 19-09-2020 9:33am

y0ssar1an22 wrote: »

your perception and experience of time is half of a static observer: has that been proven, or a conjecture?

i think infinity shouldn't be allowed. it essentially means 'going that way for a long time, but we really know' so lets call it quits'.

Time dilation has been demonstrated through experimentation:

https://en.m.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment

It’s something that scientists have to take into account with certain aspects of interplanetary space travel, due to the very high speeds involved.

As for infinity, it’s a pretty important mathematical construct. It’s very different from a sequence of unknown length: it’s a sequence where you know the length has no end.

Here’s something to chew on. So the sequence of natural numbers (whole, positive numbers) is infinite - for any number you can think of, you can always add another number to it and go higher. So there’s no end to the sequence. But, the sequence of even numbers - which only contains every second natural number - is also infinite - 2,4,6,8 etc goes on forever. The even numbers are a subset of the natural numbers - they are contained with it and do not from it’s totality - yet both sets are infinite, and therefore one is not smaller or larger than the other.

Gregor Samsa · 19-09-2020 9:42am

Chancer3001 wrote: »

What we see is only light hitting our eyes.

So when we look at a distant planet we only see what light it emitted many many years ago for example.

If i start travelling towards that planet , does what i can see speed up?

No, it doesn’t speed up, but the frequency is the light increases so you will see the object as more blue. If you were travelling away from the object, you’ll see it as more red. It’s the Doppler Effect, same as you will hear the siren of an ambulance coming towards you as a higher pitch than one static or going away from you. It’s much more pronounced and easier to observe with stars or galaxies rather than planets in our solar system, as the speeds involved are much greater, but it actually applies to anything you’re moving towards or away from at any speed.

19-09-2020 9:55am

The speed of light limit also doesn’t rule out getting from a to b faster than light you just can’t yourself exceed this speed but using things like worm holes or theoretical methods of bending or folding space you can in theory travel to places faster than light can. Even in Star Trek they need to be inside a “warp bubble” in order to achieve speeds faster than light and there is a theory about how something similar might be possible in reality - the Alcubierre drive.

It should also be noted that the universe already has clear examples of objects having move apart at speeds faster than light. Physicists have discovered based on their calculations (how they realise this is a very long answer) on the expansion of the universe from the Big Bang that objects are too far apart than would be possible even at the speed of light so this lead to the development of the theory of inflationary expansion. Which in a nutshell means that the space between objects expanded at speeds faster than the speed of light got a very short time. Because it was space that expanded between objects rather than the objects themselves moving apart no laws of physics are broken.

A good analogy would be to draw two dots beside each other on a deflated balloon. When you blow up the balloon the objects are now far apart but they haven’t moved rather than balloon has expanded and resulted in more space between then.

19-09-2020 9:57am

Gregor Samsa wrote: »

Time dilation has been demonstrated through experimentation:

https://en.m.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment

It’s something that scientists have to take into account with certain aspects of interplanetary space travel, due to the very high speeds involved.

As for infinity, it’s a pretty important mathematical construct. It’s very different from a sequence of unknown length: it’s a sequence where you know the length has no end.

Here’s something to chew on. So the sequence of natural numbers (whole, positive numbers) is infinite - for any number you can think of, you can always add another number to it and go higher. So there’s no end to the sequence. But, the sequence of even numbers - which only contains every second natural number - is also infinite - 2,4,6,8 etc goes on forever. The even numbers are a subset of the natural numbers - they are contained with it and do not from it’s totality - yet both sets are infinite, and therefore one is not smaller or larger than the other.

Infinity plus 1. Yeah, got you snookered now :pac:

Giblet · 19-09-2020 10:01am

y0ssar1an22 wrote: »

i always thought physics was essentially 1 + 1 = 2; a physical quantifiable 'thing' that you can solve for?'

it seems, there is so many unknowns, that people are happy to go along with the that, without any proof?

Maths is 1+1 = 2. You use Maths to build models in Physics, but it's just a model.

You can create many models for the same phenomena, depending on your need.

Every model is tested again and again to ensure it holds up under certain conditions and each can be used depending on how much accuracy you need. Newtonian models might represent 99% of how things work and has easier Maths to use, but we use different models for 99.9%, which require the Maths to get far more complex, therefore harder to use.

Science doesn't have proof, only Maths does, which is why Science adjusts. It's a good system.

Sky King · 19-09-2020 10:05am

Did you hear about the supersonic fart?

You can smell it before you hear it.

Smiles35 · 19-09-2020 10:05am

There was a great thread on here years ago. A first poster came on chalenging everyone to explain the old Greek term Ehther. The best bit was he would sporaticly quote pieces from Einstiens private letters. Must have been these https://www.amazon.co.uk/Born-Einstein-Letters-1916-1955-Friendship-Uncertain/dp/1349729116

The long and the short of it is. I don't have to bother with those relative velocity diagrams anymore after that.

You, see. They can't actually measure the speed of light. I can accept that. As a man, I have a limitation.

ILoveYourVibes · 19-09-2020 10:09am

y0ssar1an22 wrote: »

a question that has puzzled me for a while...

1: car A and car B have a velocity towards each other of 100 kph. they are approaching each other is 200kph.

2: if car A and car B are doing the same, but at the speed of light why are they not approaching each other at (2)(speed of light)?

if the rules of physics hold for scenario 1, why not scarios 2?

is there a simple explanation here?

i dunno, maybe we just don't have an answer?

They do ...its called superluminal speed or FTL ..(faster than the speed of light)

Thus the story ...

Actually he was faster than a speeding bullet ......but anyway...im talking junk!

blinding · 19-09-2020 10:13am

Wanderer78 wrote: »

This stuff always fascinated me, but by fcuk is it a mind bender, physics is weird!

Perhaps it you thats weird and physics if fine !

ILoveYourVibes · 19-09-2020 10:14am

blinding wrote: »

Perhaps it you thats weird and physics if fine !

am i fine too?:o

blinding · 19-09-2020 10:14am

Chancer3001 wrote: »

What we see is only light hitting our eyes.

So when we look at a distant planet we only see what light it emitted many many years ago for example.

If i start travelling towards that planet , does what i can see speed up?

Not faster than the Speed of Light.

ILoveYourVibes · 19-09-2020 10:17am

blinding wrote: »

Not faster than the Speed of Light.

I think he just enters a different time zone.

blinding · 19-09-2020 10:18am

ILoveYourVibes wrote: »

am i fine too?:o

Oh Yeah !

c montgomery · 19-09-2020 10:20am

y0ssar1an22 wrote: »

i always thought physics was essentially 1 + 1 = 2; a physical quantifiable 'thing' that you can solve for?'

it seems, there is so many unknowns, that people are happy to go along with the that, without any proof?

It's too complex an area to explain fully in a boards post. Relativity is one of the most tested theories in physics and its use is ubiquitous.
It took me years to get my head around it.

ILoveYourVibes · 19-09-2020 10:20am

blinding wrote: »

Oh Yeah !

I wuv u. x

AllForIt · 19-09-2020 10:22am

This is a very good lecture in this subject area even for a layperson to follow from Yale Uni.

Wanderer78 · 19-09-2020 10:26am

blinding wrote: »

Perhaps it you thats weird and physics if fine !

id happily accept, that both of us are weird, ive studied it for a while, it really is weird, and so am i

19-09-2020 10:31am

y0ssar1an22 wrote: »

a question that has puzzled me for a while...

1: car A and car B have a velocity towards each other of 100 kph. they are approaching each other is 200kph.

Nope, they aren't. They are approaching each other at 199.999999999998285... km/h according to relativistic velocity addition.
https://en.wikipedia.org/wiki/Velocity-addition_formula

I think you are confusing the idea that relativistic equations only apply when things are moving fast. In fact, they always apply, and Newtonian mechanics is simply a good approximation at low speeds.

Here is a graph of the above equation of your scenario of the speed of both cars being the same (u=v). Red is Newtonian and blue is Einstein. The x-axis is the speed of each car relative to a stationary observer (in units of speed of light) and the y-axis is the speed of each car according to each other (also in units of speed of light).

As each car approaches the speed of light relative to the observer, the speed of one car relative to the other incorrectly approaches twice the speed of light according to Newton (2 on the y-axis) and correctly approaches the speed of light according to Einstein (1 on the y-axis). Also, note that both agree well at low speeds and it's not that the relativistic equations "kick in" at some arbitrary high speed.

Eleven Benevolent Elephants · 19-09-2020 10:32am

Time dilates and space contracts as you approach the speed of light.

Each car will be travelling at 99.999999999999 % the speed of light but they will still only approach each other at 99.999999999 %

Btw, the cars will never reach the speed of light, it will just keep getting heavier and heavier as it approaches c. Only massless objects can reach c, photons have no rest mass but do have mass simultaneously.

the speed of light question

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