Astronomy Without A Telescope – A Photon’s Point Of View

by Steve Nerlich on August 6, 2011

The way Hollywood envisions moving at light speed doesn't really work - since it still implies that you move a certain distance over a certain time period. As far as a photon is concerned, it does neither. Source: zidbits.

From a photon’s point of view, it is emitted and then instantaneously reabsorbed. This is true for a photon emitted in the core of the Sun, which might be reabsorbed after crossing a fraction of a millimetre’s distance. And it is equally true for a photon that, from our point of view, has travelled for over 13 billion years after being emitted from the surface of one of the universe’s first stars.

So it seems that not only does a photon not experience the passage of time, it does not experience the passage of distance either. But since you can’t move a massless consciousness at the speed of light in a vacuum, the real point of this thought experiment is to indicate that time and distance are just two apparently different aspects of the same thing.

If we attempt to achieve the speed of light, our clocks will slow relative to our point of origin and we will arrive at our destination quicker that we anticipate that we should – as though both the travel time and the distance have contracted.

Similarly, as we approach the surface of a massive object, our clocks will slow relative to a point of higher altitude – and we will arrive at the surface quicker than we might anticipate, as though time and distance contract progressively as we approach the surface.

Again, time and distance are just two aspects of the same thing, space-time, but we struggle to visualise this. We have evolved to see the world in snapshot moments, perhaps because a failure to scan the environment with every step we take might leave us open to attack by a predator.

Science advocates and skeptics say that we should accept the reality of evolution in the same way that we accept the reality of gravity – but actually this is a terrible analogy. Gravity is not real, it’s just our dumbed-down interpretation of space-time curvature.

If you could include the dimension of time in this picture you might get a rough idea of why things appear to accelerate towards a massive object - even though they do not themselves experience any acceleration.

Astronauts moving at a constant velocity through empty space feel weightless. Put a planet in their line of trajectory and they will continue to feel weightless right up until the moment they collide with its surface.

A person on the surface will watch them steadily accelerate from high altitude until that moment of collision. But such doomed astronauts will not themselves experience any such change to their velocity. After all, if they were accelerating, surely they would be pushed back into their seat as a consequence.

Nonetheless, the observer on the planet’s surface is not suffering from an optical illusion when they perceive a falling spacecraft accelerate. It’s just that they fail to acknowledge their particular context of having evolved on the surface of a massive object, where space-time is all scrunched up.

So they see the spacecraft move from an altitude where distance and time (i.e. space-time) is relatively smooth – down to the surface, where space-time (from the point of view of a high altitude observer) is relatively scrunched up. A surface dweller hence perceives that a falling object is experiencing acceleration and wrongly assumes that there must be a force involved.

As for evolution – there are fossils, vestigial organs and mitochondrial DNA. Get real.

Footnote: If you were falling into a black hole you would still not experience acceleration. However, your physical structure would be required to conform to the extremely scrunched up space-time that you move through – and spaghettification would result.

Tagged as: Space-time curvature

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  • Anonymous

    Starlight

    Relativity saves the day, as usual. ;)

    Credit: xkcd.com

    • WaxyMary

      general rant–

      I like xkcd of course, who wouldn’t, but…

      The photon does not ‘die’ so we can see some pretty dots. The photon combines with material we have within our eyes and in doing so becomes a part of us for the duration as it were.

      Mary

  • Anonymous

    I think you misunderstand how the evolution-gravity analogy is used.

    The analogy makes no comparison between the facts of the theories as you describe, but uses the theory status itself as the basis of the argument.

    When an evolution doubter uses the argument “well evolution is just a theory”, the sceptic gets to smile and point out that “so is gravity, but you don’t doubt gravity’s existence based purely on its theory status”.

    • Anonymous

      I’m not sure what you’re getting uptight about, I wasn’t criticising the article, just saying that in my experience “science advocates and skeptics” don’t say anything like what you suggested. That fact still stands.

    • http://www.facebook.com/Dr.Nothing Jeffrey Scott Boerst

      Gravity is a law. A law in scientific terms is basically an indisputable, automatically experienced and conceivable concept. Drop something and it falls. Hit something and it breaks in proportion to amount of energy in the force of the hit, etc… Laws are at the ‘beginning’ of the scientific method. They are the building blocks of theories. Theories are ideas (hypotheses) that use a set of laws, arranged in a certain way that can imaginably, when set in motion, achieve a predictable outcome; like a series of lined dominoes knocked over that perform various physical actions such as triggering a series of flags to pop up when a catch is released by a domino hit and so on… Laws are universal and unchanging… theories can always be tweaked and refined to describe these sequences of events in more detail.

      • Anonymous

        Gravity is both a law and a theory; the theory of gravity encompases the laws of gravitation. It is to the theory of gravity we refer when countering the evolution is just a theory argument.

        The theory of gravity contains many aspects which can be tweaked and refined, just as the theory of evolution contains many aspects which can be tweaked and refined. Incidentally, a scientific hypothesis is not the same as a scientific theory.

        But regardless of the specifics, this is not the point that I was making, which was that the evolution-gravity analogy is not used by sceptics and science advocates in the way that the article suggests.

        For the curious, you can read about the difference between laws, theories, hypotheses at http://wilstar.com/theories.htm and find out more about the evolution-gravity analogy at http://en.wikipedia.org/wiki/Evolution_as_theory_and_fact#Evolution_compared_with_gravity

      • WaxyMary

        @Jeffrey Scott Boerst,

        I like your way of telling the story. I also like the laws described in I Think We’re All on this Bus, the section on the wall of science. “Push Something Hard Enough And It Will Fall Over.” — Fudd’s First Law of Opposition as well there is “What Goes In, Must Come Out.” — Teslacle’s Deviant to Fudd’s First Law.

        But seriously folks, I’m here all week, don’t forget to tip your wait staff.

        Mary

  • Torbjörn Larsson

    50 + comments! What have you wrought, Nerlich?

    To take lcrowell’s and Colin Kline’s start and run with it, special relativity permits a perhaps nice POV model of the quantum field. Or I like to think so:

    It is my understanding (disclaimer: no quantum field studies) that if you start with the classical mechanics particle, you go over the classical electromagnetic field picture of Maxwell, to end in the quantum field as a global special relativity property of local particle interactions.

    The photon is the classical field’s way of propagating energy in a Poynting energy flow as radiation. That gives the broad-lobe 1/r2 radiation behavior of EM fields, which supplements the 1/r2 static behavior of infinite range fields from Gauss’s law.

    Since the quantum field is neither particle nor field but a particle field, you can as momentarily forget the photon existence between creation and extinction and see it as a field property of the field.

    Please note that this is not physically accurate _at all_ since it is radiation that propagates, not the field. But it gives a facile (“easifying”?) analogy of the photon as “emitted and then instantaneously reabsorbed”.

    @ Nerlich:

    Science advocates and skeptics say that we should accept the reality of evolution in the same way that we accept the reality of gravity – but actually this is a terrible analogy. Gravity is not real, it’s just our dumbed-down interpretation of space-time curvature.

    It is a good analogy. It is used to reflect the difference between fact, such as existence of gravity, and theory, such as different theories of gravity.

    One use is the one morphics mention. Another is to relate observing evolution between species (populations) as fact with a simple observation of falling things as fact. Then I use to go on to illustrate evolution as the simplified “variance+selection” instead of the modern synthesis, in the same way that you use newtonian gravity instead of general relativity at times.

    I believe you mean it is a terrible description of gravity. But that is not the purpose of the analogy, at all.

    And as always, analogies are faulty but useful illustrations of principles, not precise equivalences. There is no need to protect the beauty of gravity; it stands on its own. (But there is plenty of need to protect the beauty of evolution, for that matter.)

  • Anonymous

    If a photon emitted from one of the first stars is observed by a human having travelled for 13 billion years and has changed position, wavelength etc but occurs instantaneously from the photons point of view, does this mean that information is created instantaneously?

    • WaxyMary

      @NoviceGaz,

      You ask an interesting question from the point of view of the photon.

      The answer seems to be (from the point of view of the photon) that the non-distance is crossed in no-time.

      A few more thoughts though, since your question is stirring the waters of my magic 8 ball.

      The no distance/no time is also expected to be filled with the accelerated expansion of the space-time which further begs this question -does the photon experience any of the effects of the expansion and the acceleration of that expansion.

      Does the photon actually carry any information, any data, which relates to the trip it has been on for all those years?

      Implied herein is, some data is carried by the photon, more than just what we measure at our end; duration is not an experience that is carried individually by any one photon though.

      There seems to be only a few thing a photon ‘knows’; duration and distance are not among the select few it would seem. The frequency and the energy density are the only two items a photon knows to our measure, if memory serves me well today. Now any group of photons can be tracked via statistical analyses of various types for various purposes.

      The data we extract from those equations may be data which is commonly carried by each, subjected to the whole we have measured, but we would never be able to assign any spec of that to any point of that mass of photons. The group is not quite the whole though, when single photons are measured, this also means the way that measurement takes place, the method, has some impact on that single photon when taken from the whole, or from the group.

      Duration is part of the travel of the photon which it does not experience, hence no tired light, if you would. Our measurements imply that duration has passed, and how the photon has arrived at our ‘door’, the path it has taken. We can’t inform the photon though, it has no place to carry that datum set. It has no ticket for our conductor to punch.

      Distance (already expanded, or that which will be expanding faster) is another thing the photon is unaware of being crossed, hence no foot weary light, if you would. The change which does occur to the photon’s frequency due to the expansion does not impress itself as any change in state, nor as any remembered state in fact, that we can tell. Any changes of state at our end seem to be some part of the original state to the photon, and to us, of course. We assign the most probable cause for that change state, indeed that a state is in change at some point along the path taken is one of many assumptions our theories grant. There are no stations, no crossings, no milk train travels for the photon because if it had a ticket that ticket would be for the express train.

      We conclude these facts from our measurements and those math laden theories freshmen learn to ‘love’.

      We test them and test them, these theories, and it seems the theories hew to, cleave to the line we have traced. When something new comes along, and it does, never fear, it too is added or subtracted and included in out tests.

      The abilities, the nature, of any photon which completes the trip from there to here, wherever there is, is implicit within our grasp of that photon. We can’t measure what we do not ‘see’ as it were.

      This has been fun, try another question, says the magic 8 ball.

      Mary

    • Torbjörn Larsson

      Very interesting question.

      “Information” is relative a system. Here, photons can be used to encode messages, but it is known that the information is not in the single photon (phase velocity) but in a bunch of them (group velocity). In many situations it is the wave front that encodes the information.

      Stretching light means it will tell you of cosmological redshift. But only if you have several photons, so you can see that in a spectra of stars (absorption or emission lines) or CMB (black body temperature).

      In other words, a single photon doesn’t encode (“experience”) the fact that it has been stretched. That reflects the fact I noted above, that information is relative systems, here the whole physics of spectra vs redshift.

  • Anonymous

    Mr. Nerlich’s piece opens-up a fascinating space-time corridor of thought-entry doors:

    Just one that may lie beyond the vanishing point. Read something some while ago, that made me realize that absolutely nothing in “space” is motionless: Earth rotates on its axis, revolves around Sun ( in Moon dance ); the Sun, in turn, moves in its stellar neighborhood.

    Journey farther out from that insignificant local star group, and a larger constellation of groupings comes into perspective, a diverse star field suspended between(?) two huge spiral Arms: Our relatively small local star assembly, itself flowing along with the even bigger regional celestial mass. These scaled-up motions adding-to that of the aforementioned.

    Then, in the realm of the incomprehensibly gigantic, the entire Island Universe of our galactic home, with its vast rotational, Spiral movement. And that, within the even greater swarming motions of the whole “Local Group” of gravitationally related Galaxies. ( Can anyone fallow the curvature of space through all this? )

    Venturing beyond its familiar collective light, we set off into the colossal, fathomless scales of night: Entering the dominion of giants — Galaxy Clusters and Super-Clusters: whole “walls”, “sheets” and “filaments” of galaxies.

    On each quantum leap of scale, one-set of time differentials fades before a larger, enclosing array of space-time measures ( million-year galaxy turn, for example ). And in that journey through these increasingly wide time chambers of space, you have all the compounding, accumulated motions ( if I even grasp the edge of these awesome things ).

    So how fast the Earth, or anything is actually moving ( or anything related thereto ) — in reference-frame of the entire Universe — may be any body’s guess. What is the ultimate point of determination? Is it all, indeed, relative? How superimposed time-layering figures-in, is light years beyond my ken.

    Complex Clockwork assembly came to mind: Motions within motions, times within times. Wheel and gear differentials,
    concentric time cycles: A second turn, a minute spin, an hour revolution — and a billion-year twirl of a Super Cluster Filament!

    Just one, non-technical door of thought that may go nowhere ( did I hear it close behind me? )

  • Anonymous

    Problem: translocating the particles/information p that constitute me (or you) to places outside of Earth takes t = too damn long. Solution = nowhere in what we know so far. Suggestion:stop being so smug about it and look again.

    • Anonymous

      We are! It just takes time…

  • Anonymous

    As Steve Nerlich points out, when considering a photon’s point of view, the distance it travels and time elapsed are zero: This is a consequence of special relativity. As far as the photon is concerned, the universe is a timeless, spaceless point. This underscores the basic dichotomy between classical and quantum physics. From a quantum point of view, effects like tunnelling, entanglement, and the superposition of states supersede space and time. The photon and the information it bears are “everywhere at once.” However, from our “classical” point of view, space and time do exist. The photon travels 13 billion light-years and takes all that time to deliver its information. So which POV “rules?” According to Steven Hawking and others, it may be that the quantum point of view is fundamental while the “classical” view is secondary: Space and time might ultimately emerge from the decoherence (wave-function collapse) of quantum states. (See Scientific American – June 2011.)

  • Anonymous

    As Steve Nerlich points out, when considering a photon’s point of view, the distance it travels and time elapsed are zero: This is a consequence of special relativity. As far as the photon is concerned, the universe is a timeless, spaceless point. This underscores the basic dichotomy between classical and quantum physics. From a quantum point of view, effects like tunnelling, entanglement, and the superposition of states supersede space and time. The photon and the information it bears are “everywhere at once.” However, from our “classical” point of view, space and time do exist. The photon travels 13 billion light-years and takes all that time to deliver its information. So which POV “rules?” According to Steven Hawking and others, it may be that the quantum point of view is fundamental while the “classical” view is secondary: Space and time might ultimately emerge from the decoherence (wave-function collapse) of quantum states. (See Scientific American – June 2011.)

  • Anonymous

    Some of the right idea is here, but you need a sign difference between the spatial parts and the (ct)^2 part. This makes the metric pseudo-Euclidean or Lorentzian. With a strictly Euclidean metric there is no situation where ds = 0 without the elements dt = dx = … = 0.

    LC

  • Baksa Péter

    Wow, I didn’t know that there’s no space for a photon.

    >It’s just that they fail to acknowledge their particular context of having evolved on the surface of a massive object, where space-time is all scrunched up.

    Our deficiency at perceiving the 4th dimension (and therefore making wrong assumptions) is maybe more because we can’t move in it at free will, not because it is scrunched up.
    It would make sense for our brain to compute in 4D spacetime if it could alter our speed in time, but in 3D it is more convenient to compute with apparent forces and a constant time.

  • WaxyMary

    You do mean Basic Science, right Tim?

    Mary

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