Does Photon Emission Influence Celestial Body Movement?

[Bjarne]

What evidence proves that photon emission of an object, - at all sends some of its momentum back to the source, - and thereby cause it to decelerate (or move opposite)?

Or what is the evidence proving that photon emission at all do have a decelerating influence on the object emitting the photons?

Are the Earth and the Moon also pushed away from the Sun due to photon emission / reflection? - I guess no, not at all.

 

[0xDEADBEEF]

Look up radiation pressure. Also: due to the conservation of momentum anything that emits more light in one direction than the other one will be pushed. There have been simulations that show results compatible with the Pioneer anomaly so most people say that the issue is resolved. We don't need to question an established theory like general relativity if there is no hard evidence against it.

 

[Bjarne]

Look up radiation pressure.

I have read about it. It is easy to accept this part.
It seems to be logical that the pressure is real so long something (matter) is hit by photons.
But it still seems to me that photons bombarding a piece of matter, - is very different from photons bombarding empty space (as reflecting photons from the Pioneer spacecraft did).

Also: due to the conservation of momentum anything that emits more light in one direction than the other one will be pushed.

Which scientific evidence are we now talking about?

There have been simulations that show results compatible with the Pioneer anomaly so most people say that the issue is resolved.

Most people say so much. Science must be based on the scientific method; otherwise it is not science to me.

We don't need to question an established theory like general relativity if there is no hard evidence against it.

To my opinion, - test of relativity is always necessary until all aspect are proven by the scientific method.

It don’t seem logical to me that "due to the conservation of momentum anything that emits more light in one direction than the other one will be pushed"
Simply because how can pressure exist so long the bombardment is against empty space?

• Which scientific evidence is supporting this part?
• Does any experiment or observation support that?
• Why do you think relativity should lead to such conclusion?

 

[TurtleMeister]

It don’t seem logical to me that "due to the conservation of momentum anything that emits more light in one direction than the other one will be pushed"
Simply because how can pressure exist so long the bombardment is against empty space?

• Which scientific evidence is supporting this part?
• Does any experiment or observation support that?
• Why do you think relativity should lead to such conclusion?

How can it not be logical? If radiation pressure exists, and has been experimentally observed, then by Newton's third law of motion and the conservation of momentum, the source of that radiation must also experience a force in the opposite direction. Do you really need experimental evidence for this? Empty space has nothing to do with it.

 

[Vanadium 50]

Momentum is conserved. The fact that light carries both momentum and energy is both theoretically and experimentally established. Arguing otherwise will get this thread locked very quickly.

 

[Bjarne]

How can it not be logical? If radiation pressure exists, and has been experimentally observed, then by Newton's third law of motion and the conservation of momentum,

It seems to be some “missing link here”, that's all.
Newton’s third law is based on simple mechanic. This question here is not that simple. At least not to me.

the source of that radiation must also experience a force in the opposite direction.

Well, let’s now follow the photon leaving the space probe, let’s say it was emitted towards the Sun, (towards the antenna) - the emission should now instantly push the spacecraft forward, (opposite the Sun) - whereby the space probe must accelerate, not decelerate.

The next thing that happens is the photon is hitting the antenna, and is changing direction; and then zig zag now towards the space probes motion direction.

Let's say the reflected photon exert a similar influence, the space probe must now decelerate due to the backwards push towards the new direction, - but since the emission caused acceleration initially, - the net result must cancel out? –and hence zero - or?

Momentum is conserved. The fact that light carries both momentum and energy is both theoretically and experimentally established. Arguing otherwise will get this thread locked very quickly.

I am not arguing otherwise, but just asking how we can distinguish between what is proven by the scientific method and what is not. The Pioneer Anomaly has for decades been a mystery, now we are ready to close that chapter, - how sure can we be that we not just are closing our eyes?

I am always willing to accept scientific facts, - But how can I be sure when something not is proven by the scientific method?

There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any question, to doubt any assertion, to seek for any evidence, to correct any errors.
Robert Oppenheimer.

 

[Drakkith]

It seems to be some “missing link here”, that's all.
Newton’s third law is based on simple mechanic. This question here is not that simple. At least not to me.

It is exactly that simple. The complicated part is calculating the exact effects of the radiation pressure emitted from the spacecraft 's different parts.

Well, let’s now follow the photon leaving the space probe, let’s say it was emitted towards the Sun, (towards the antenna) - the emission should now instantly push the spacecraft forward, (opposite the Sun) - whereby the space probe must accelerate, not decelerate.

Most of the heat producing electronics are behind the main dish, so the radiation emitted from both sides of the spacecraft are unequal, with most of it being directed in the direction the spacecraft is moving.

I am not arguing otherwise, but just asking how we can distinguish between what is proven by the scientific method and what is not. The Pioneer Anomaly has for decades been a mystery, now we are ready to close that chapter, - how sure can we be that we not just are closing our eyes?

We can't. We can't be sure of anything. Ever. However new calculations show that when you include the radiation pressure from the spacecraft , no anomalous acceleration remains. IE the effect can be explained by thermal emission from the spacecraft and doesn't require any new physics.

I am always willing to accept scientific facts, - But how can I be sure if something not is proven by the scientific method?

The scientific method proves nothing. It is merely a way to find possible solutions to problems. You can never prove anything 100%.

 

[Bjarne]

It is exactly that simple. The complicated part is calculating the exact effects of the radiation pressure emitted from the spacecraft 's different parts.

I would say it is more complicated to know whether we are on the right track, so long there are no real scientific evidence.

Most of the heat producing electronics are behind the main dish, so the radiation emitted from both sides of the spacecraft are unequal, with most of it being directed in the direction the spacecraft is moving.

Right but as I wrote the zig zig path of the photon can be compared to by turns to get slaps at the right and left cheek, - which way will the man finally fall ? To the right or to the left?

We can't. We can't be sure of anything.Ever.

Ahh come on. I feel myself pretty sure that Venus orbit the Sun, not the Earth.

However new calculations show that when you include the radiation pressure from the spacecraft , no anomalous acceleration remains. IE the effect can be explained by thermal emission from the spacecraft and doesn't require any new physics.

That’s right, but notice many articles claims this is "the most likely reason".
I am not so convinced; you can program a software the way you want. A computer only does what it is told to. Imaging the photons would zig zag between the antenna and the main ship forever, - honestly - would that not just forever cancel out the opposite impact influences?
Which different does it make if the photons escape the trap after short time? – So long they are zig zag towards opposite direction of the space probes, - the result seems to me, - must be about zero.

The scientific method proves nothing. It is merely a way to find possible solutions to problems. You can never prove anything 100%.

I can prove that my thump is to the left on my right hand and opposite on the left hand. This is based on observation and hence based on the scientific method. . But I cannot see what the photons does and not does. nobody can, also not NASA, - That’s the differences.

Never the less, what i do see at the drawing seems to be a zero result. - But in this case I agree we don't know, we only believe the Pioneer Anomaly maybe is solved, because this is what we are told to believe.


There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any question, to doubt any assertion, to seek for any evidence, to correct any errors.
Robert Oppenheimer.

 

[Drakkith]

I would say it is more complicated to know whether we are on the right track, so long there are no real scientific evidence.

There is plenty of evidence. We know how radiation pressure works and can measure it to a very precise value in experiments. Just because we aren't physically there doesn't mean we can't apply it to the Voyager probe. Applying known science to solve problems is exactly what you are supposed to do. In this case we had a problem, re-examined it and applied known physics, and the end result eliminated the problem. This is EXACTLY how almost all problems are solved in life.

Right but as I wrote the zig zig path of the photon can be compared to by turns to get slaps at the right and left cheek, - which way will the man finally fall ? To the right or to the left?

Your diagram is incomplete. Radiation is being emitted in different directions, not just from the dish towards the electronics. Besides, the final direction the photon moves in is what matters, not how many times it is reflected. Those reflected photons will eventually be reflected away from the spacecraft in the direction of motion since they originated on that side of the dish.

Ahh come on. I feel myself pretty sure that Venus orbit the Sun, not the Earth.

There is no way to prove it absolutely. A sufficiently complicated set of rules could duplicate our measurements but have Venus be the center of the universe or something.

That’s right, but notice many articles claims this is "the most likely reason".
I am not so convinced; you can program a software the way you want. A computer only does what it is told to.

This has nothing to do with a computer, it only does the math for us. Real people were in charge of finding solutions, and several had been presented prior to a detailed analysis of the radiation pressure.

Imaging the photons would zig zag between the antenna and the main ship forever, - honestly - would that not just forever cancel out the opposite impact influences?
Which different does it make if the photons escape the trap after short time? – So long they are zig zag towards opposite direction of the space probes, - the result seems to me, - must be about zero.

They do not zig zag forever. They will either be absorbed or reflected away from the spacecraft . Absorbed photons end up imparting no net acceleration, while reflected ones do.

I can prove that my thump is to the left on my right hand and opposite on the left hand. This is based on observation and hence based on the scientific method. . But I cannot see what the photons does and not does. nobody can, also not NASA, - That’s the differences.

No, you cannot prove that with absolute certainty. The fact that you even think you can points out that you don't understand the scientific method.

 

[Bjarne]

There is plenty of evidence. We know how radiation pressure works and can measure it to a very precise value in experiments. Just because we aren't physically there doesn't mean we can't apply it to the Voyager probe. Applying known science to solve problems is exactly what you are supposed to do. In this case we had a problem, re-examined it and applied known physics, and the end result eliminated the problem. This is EXACTLY how almost all problems are solved in life.

I am not so sure. I have tried to Google exactly which kind of experiments proves that photon bombardment really can accelerate an object. I only found some superficially descriptions of experiments done long ago.

I would be happy to get some better links to read more about such experiments. - But "plenty of "evidence" ? - Remember everything can be interpreted different, - for example if the devil read the bible it is not sure it would be understood the same was as when we do. ´

I also notice that plenty of experiments failed to prove the predicted influence. So in its very basic I am not convinced that photons bombardment really can force anything to move. - No doubt that photons can be absorbed and that this will increase the energy (and "pressure") of an object, but this I believe we both agree is something very different.

Your diagram is incomplete. Radiation is being emitted in different directions, not just from the dish towards the electronics. Besides, the final direction the photon moves in is what matters, not how many times it is reflected. Those reflected photons will eventually be reflected away from the spacecraft in the direction of motion since they originated on that side of the dish.

I could very easy accept that impact of photon really has the predected influence, simply because this part sound logical. Still I would like to have that confirmed and read which experiemt did really prove that.

Besides, the final direction the photon moves in is what matters

Here is the bone of content...
I mean the direction from where an impact comes from matter; - Yes this sound acceptable and logical.
But the direction the photon moves after hitting something - does that really matter?
What exactly is the evidence for that part?
I am asking for a specific experiment that proves that idea.
This part is really very hard to swallow.

There is no way to prove it absolutely. A sufficiently complicated set of rules could duplicate our measurements but have Venus be the center of the universe or something.

I am happy so long things sound rational and logical, or at least really are proven by experiments or direct observation. I cannot accept hokus pokus science.

This has nothing to do with a computer, it only does the math for us. Real people were in charge of finding solutions, and several had been presented prior to a detailed analysis of the radiation pressure.

I think we have reached the "bon of content" as I wrote above.
The data that feeds the computer is off course important, - if that part is on really thin ice, the whole solution is too.

No, you cannot prove that with absolute certainty. The fact that you even think you can points out that you don't understand the scientific method.

http://www.tomatosphere.org/teacher-resources/teachers-guide/images/scientific-method.jpg

The method is simple, we could for example replicate the experiment, build 2 new Pioneer probes, let them move towards the same direction, BUT replace the heat emitter so that heat NOT is reflected.
And parallel with that also launch 2 copy of the old Pioneer probes, on the same time/ path...
Now 2 probes should decelerate and the 2 new models not.
Is that what would happen?
In this case experiments and the scientific method have taken over.
Such would to me be very acceptable, logic and rationel science. Science approved by experiments, and hence by the scientific method.

We have seen too many times that our conclusions and expectation were wrong, - such is not science.

 

[Drakkith]

I am not so sure. I have tried to Google exactly which kind of experiments proves that photon bombardment really can accelerate an object. I only found some superficially descriptions of experiments done long ago.

I don't see why you need modern experiments if the original ones prove this effect. For example here is the original device used to measure it. http://en.wikipedia.org/wiki/Nichols_radiometer
Here's the link to the actual journal the results were published in: http://www.scribd.com/doc/76312661/...Annalen-Der-Physik-Pyotr-Lebedev-1901-English
You could probably make one at home.

I would be happy to get some better links to read more about such experiments. - But "plenty of "evidence" ? - Remember everything can be interpreted different, - for example if the devil read the bible it is not sure it would be understood the same was as when we do.

´

Your personal interpretation is irrelevant. The fact is that radiation pressure is used extensively in astronomy and astrophysics. For example I just read today in Sky and Telescope magazine about how the emission of radiation influences asteroid rotation rates and can cause them to spin up fast enough for a piece of it to actually break off. Page 32, December 2012 issue. Here's a link to the YORP effect as it's named: http://en.wikipedia.org/wiki/Yarkovsky–O'Keefe–Radzievskii–Paddack_effect
Also, here's an actual research paper that uses it: http://arxiv.org/abs/1210.2219
Heck, here's a link where you can see all kinds of research papers involving it: http://arxiv.org/find/all/1/all:+yorp/0/1/0/all/0/1

I also notice that plenty of experiments failed to prove the predicted influence. So in its very basic I am not convinced that photons bombardment really can force anything to move. - No doubt that photons can be absorbed and that this will increase the energy (and "pressure") of an object, but this I believe we both agree is something very different.

Here's info on a solar sail, which has been used in real life to move an actual spacecraft . http://en.wikipedia.org/wiki/Solar_sail

Here's the explanation of radiation pressure. Note that reflected radiation imparts twice the momentum. http://en.wikipedia.org/wiki/Radiation_pressure

Here is the bone of content...
I mean the direction from where an impact comes from matter; - Yes this sound acceptable and logical.
But the direction the photon moves after hitting something - does that really matter?
What exactly is the evidence for that part?
I am asking for a specific experiment that proves that idea.
This part is really very hard to swallow.

Newtons laws of motion, conservation of momentum, and plenty of others. If a photon is reflected or emitted in a direction it MUST impart a force in the opposite direction due to conservation of momentum. The Nichols Radiometer is a perfect example of this.

The method is simple, we could for example replicate the experiment, build 2 new Pioneer probes, let them move towards the same direction, BUT replace the heat emitter so that heat NOT is reflected.
And parallel with that also launch 2 copy of the old Pioneer probes, on the same time/ path...
Now 2 probes should decelerate and the 2 new models not.
Is that what would happen?
In this case experiments and the scientific method have taken over.
Such would to me be very acceptable, logic and rationel science. Science approved by experiments, and hence by the scientific method.

This is nonsense. It is a complete waste of time and money to build new spacecraft and launch them into an escape orbit just to see if radiation pressure is really the culprit.

The REAL issue I see here is your unwillingness to trust that scientists know what they are talking about because it doesn't sound logical to you. Also, consider that the internet hasn't been around for the most of scientific history, so many of the initial experiments that established basic laws, and subsequent ones that further refined them, simply aren't available online in a word for word copy unless you know where to look. Most experiments were published in journals that may or may not have been copied to an online format. In many cases they have, as I've seen more than a few links to an article in Annalen der Physik, a popular scientific journal that even Einstein used. Even today many experiments are published in for-profit journals and cannot be found online without paying.

 

[Bjarne]

I don't see why you need modern experiments if the original ones prove this effect. For example here is the original device used to measure it. http://en.wikipedia.org/wiki/Nichols_radiometer
Here's the link to the actual journal the results were published in: http://www.scribd.com/doc/76312661/...Annalen-Der-Physik-Pyotr-Lebedev-1901-English
You could probably make one at home.

Thank's for all the links.

Newtons laws of motion, conservation of momentum, and plenty of others. If a photon is reflected or emitted in a direction it MUST impart a force in the opposite direction due to conservation of momentum. The Nichols Radiometer is a perfect example of this.

I have not fully understood that experiments, a lof of speciel technical terms are used, and english is not my first language. I need more time.
Can you short explian why you think the Nichols Radiometer proves that reflected radiation imparts twice the momentum.

If a photon is reflected or emitted in a direction it MUST impart a force in the opposite direction due to conservation of momentum.

How is that possible, how can the photon transfer kinetic energy to the object it hit, and at the same time not lose energy (or momentum) ?

 

[mfb]

How is that possible, how can the photon transfer kinetic energy to the object it hit, and at the same time not lose energy (or momentum) ?

If the object gains kinetic energy, the photon will lose some (and get red-shifted). This happens if the spacecraft moves in the same direction as the photon in your reference frame.

 

[Drakkith]

I have not fully understood that experiments, a lof of speciel technical terms are used, and english is not my first language. I need more time.
Can you short explian why you think the Nichols Radiometer proves that reflected radiation imparts twice the momentum.

I'm not sure how to answer that. Because we measure the amount of light and how much is absorbed and reflected, and then how far the radiometer moves? I doubt that this single experiment is the sole example of this effect.

 

[Bjarne]

I'm not sure how to answer that. Because we measure the amount of light and how much is absorbed and reflected, and then how far the radiometer moves? I doubt that this single experiment is the sole example of this effect.

I think you are right accorindg to the photon radiation push
I must say after reading it seems to be very logical and not hokus pokus as science sometimes also can be.

I notice this

Is this is the final word on it?
We still have an uncertainty in our study of less than 18 per cent. But for me, this is the answer. Some may argue it is not final, but in my mind we did a good job and it's very clear what happened.
http://www.newscientist.com/article...rious-pioneer-anomaly-this-is-the-answer.html

18%,is to my opinion too much.

The speed of the Pioneer Proves was about 12000 m/s
Do you know how that is measured?
I know it is based on blueshifted signals, but I think about time / distance factors.

Are there an easy way, that we can say it is based on the Probe time / distance reference frame (second by second)?

How is the calculation actually done?
I expect a couple of equation are used.
What about Shapiro delay

 

[Drakkith]

18%,is to my opinion too much.

Given the complex set of circumstances, the unknown physical state of the spacecraft , the still mostly unknown conditions at the edges of the solar system, and plenty of other concerns I'd say 18% uncertainty is pretty good.

 

[mfb]

18% uncertainty on what, and 18% relative to what?

If the uncertainty on the effect of radiation emission is 18%, and the deviation between prediction and measured "anomaly" is within 20%, there is no anomaly left. It would be nice to get better predictions, but that is optional.
If there is an 18%-deviation between prediction and measured anomaly and the uncertainty on the prediction is below 5%, that would be a serious issue.

hokus pokus as science sometimes also can be.

I hope you do not mean physics here.

Do you know how that is measured?

Doppler shift of radio signals. They are redshifted, as pioneer is flying away from us.
That cannot be measured second by second, as the signal itself needs hours to reach the probe. You have to consider the velocity of Earth (and its change in the orbit), the rotation of Earth and probably several other effects. Gravitational time dilation cancels as the signal goes both ways.

 

[Bjarne]

Doppler shift of radio signals. They are redshifted, as pioneer is flying away from us.
That cannot be measured second by second, as the signal itself needs hours to reach the probe. You have to consider the velocity of Earth (and its change in the orbit), the rotation of Earth and probably several other effects. Gravitational time dilation cancels as the signal goes both ways.

Right I wrote "measure", but I meant, how is the distance calculated?

 

[mfb]

The distance can be evaluated via timing - not very precise, but probably good enough as the probes are far away from any massive object and their position is not so crucial.

 

[Bjarne]

The distance can be evaluated via timing - not very precise, but probably good enough as the probes are far away from any massive object and their position is not so crucial.

It must be important that we know which distance we expect the space probes to be
Also a way of calculating this ?

 

[Drakkith]

Try this link: http://www.au.af.mil/au/awc/awcgate/jplbasic/bsf13-1.htm
And here: http://www2.jpl.nasa.gov/basics/bsf13-1.php

 

[SHISHKABOB]

It must be important that we know which distance we expect the space probes to be
Also a way of calculating this ?

We do that by sending a message out and waiting for a response. The time that it takes the message to get back will tell us how far away the probe is.

 

[Bjarne]

The gravitational field of the Earth is causing the signal to blueshift and the speed to the sigal to redshift, so this is how we measure the speed . OK

Let us say that right now we expect the speed of the space probe to be12000m/s

Let us say that time is ticking 1 nanosecond faster at the space probe (due to gravitational time dilation) as 1 second on the Earth. .

Do we expect the space probe to move 12000 m/s (per 1 Earth second) or 12000 m/s (per 1 Space probe second) ?

(To keep it simple ignore the influence of SR, so only GR influence is the question )

 

[mfb]

Let us say that right now we expect the speed of the space probe to be12000m/s

In which reference frame? ;)

Do we expect the space probe to move 12000 m/s (per 1 Earth second) or 12000 m/s (per 1 Space probe second) ?

Depends on the answer to my question.

The measurement is done on earth, but you can transform it to other systems as well of course.

 

[Bjarne]

In which reference frame? ;)Depends on the answer to my question.

The measurement is done on earth, but you can transform it to other systems as well of course.

In the frame of the space probe
Let's say right after launch the speed seen from that reference frame is exactly 12000 m/s
After some decades when leaving the solar system times ticks faster compared to time on Earth, seen from the space probe reference frame.

How fast will the speed of the space probe be after reaching the edge of the solar system, - still seen from the perspective of the space probe ?

I guess still 12000 m/s , also even though that time now is ticking faster as before??

And seen from the perspective of Earth it will look like the probe is acceleration, proportional to the time dilation, - or ?

We will ignore the backwards pulls due to gravity of the solar system

 

[mfb]

If we expect the probe to move 1200m/s relative to the sun in the system of the probe, we expect it to move 1200m/s in the system of the probe and with its own clock. Well, it has no precise atomic clock, but we can imagine one. I don't get the point.

How fast will the speed of the space probe be after reaching the edge of the solar system, - still seen from the perspective of the space probe ?
[...]
We will ignore the backwards pulls due to gravity of the solar system

Gravity will decelerate the probe (relative to the sun), this effect is always dominant unless you are close to a black hole. You have to take both effects into account if you want to compute the velocity of the probe in the system of the probe.

And seen from the perspective of Earth it will look like the probe is acceleration, proportional to the time dilation, - or ?

No.

 

[Bjarne]

If we expect the probe to move 1200m/s relative to the sun in the system of the probe, we expect it to move 1200m/s in the system of the probe and with its own clock. Well, it has no precise atomic clock, but we can imagine one. I don't get the point.

So what you say is, if we assume it was a atomic clock on bours the speed would be constant, - = 12000 m/s the whole way of of the solar system, - if we ignore the deceleration due the gravity of the solar system ?

Bjarne wrote
And seen from the perspective of Earth it will look like the probe is acceleration, proportional to the time dilation, - or ?
Mfb wrote
No.

Because the clock is ticking slower on Earth compared to on board the space probe, - the speed of the space probe cannot be understood also as 12000 m/s seen from the reference frame (hereafter RF) of the Earth too. (seen from the reference frame of the space probe)

Do you mean the speed also is 12000 m/s seen from the RF of the Earth?, - that wouldn’t be possible.'

Because time is ticking comapable slower on Earth, we on Earth cannot agree that speed is the same as seen from the perspective of the space probe, - (or ?)

What is the solution to that?

 

[mfb]

So what you say is, if we assume it was a atomic clock on bours the speed would be constant, - = 12000 m/s the whole way of of the solar system, - if we ignore the deceleration due the gravity of the solar system ?

No. In addition, you cannot ignore it. It is like asking "ignoring gravity, how quick does an apple fall?".
If we ignore deceleration, we have to ignore gravitational time dilation as well, as they are both parts of the same effect (gravity). You cannot get one without the other. Without gravity, both Earth and the probe will measure 12000m/s all the time.

Because time is ticking comapable slower on Earth, we on Earth cannot agree that speed is the same as seen from the perspective of the space probe, - (or ?)

Right, we and the probe measure different relative velocities probe<->sun.

 

[Bjarne]

No. In addition, you cannot ignore it. It is like asking "ignoring gravity, how quick does an apple fall?".
If we ignore deceleration, we have to ignore gravitational time dilation as well, as they are both parts of the same effect (gravity). You cannot get one without the other. Without gravity, both Earth and the probe will measure 12000m/s all the time.

I am not ignoring it but just trying to keep the question simple.
So what you say is that the speed out of the solar system, seen from the perspective of the space prove is "constant" - but MINUS the deceleration due to gravity ?

 

[mfb]

If you calculate the deceleration in the system of the probe.
If you calculate the deceleration in the system of earth, you get a different value due to gravitational time dilation.

You can calculate the system as a whole, but it is quite pointless to split it in arbitrary components to compare them.