Does light experience time?

May 08, 2014 by Fraser Cain, Universe Today
NGC 6791 – The full Hubble Advanced Camera for Surveys field (top right) is full of stars estimated to be 8 billion years old. Bottom right: The blue circles identify hotter dwarfs that are 4 billion years old. The red circles identify cooler dwarfs that are 6 billion years old. Credit: NASA, ESA, and L. Bedin (STScI)

Have you ever noticed that time flies when you're having fun? Well, not for light. In fact, photons don't experience any time at all. Here's a mind-bending concept that should shatter your brain into pieces.

As you might know, I co-host Astronomy Cast, and get to pick the brain of the brilliant astrophysicist Dr. Pamela Gay every week about whatever crazy thing I think of in the shower. We were talking about photons one week and she dropped a bombshell on my brain. Photons do not experience . [SNARK: Are you worried they might get bored?]

Just think about that idea. From the perspective of a photon, there is no such thing as time. It's emitted, and might exist for hundreds of trillions of years, but for the photon, there's zero time elapsed between when it's emitted and when it's absorbed again. It doesn't experience distance either. [SNARK: Clearly, it didn't need to borrow my copy of GQ for the trip.]

Since photons can't think, we don't have to worry too much about their existential horror of experiencing neither time nor distance, but it tells us so much about how they're linked together. Through his Theory of Relativity, Einstein helped us understand how time and distance are connected.

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Let's do a quick review. If we want to travel to some distant point in space, and we travel faster and faster, approaching the speed of light our clocks slow down relative to an observer back on Earth. And yet, we reach our destination more quickly than we would expect. Sure, our mass goes up and there are enormous amounts of energy required, but for this example, we'll just ignore all that.

If you could travel at a constant acceleration of 1 g, you could cross billions of light years in a single human generation. Of course, your friends back home would have experienced billions of years in your absence, but much like the mass increase and energy required, we won't worry about them.

The closer you get to , the less time you experience and the shorter a distance you experience. You may recall that these numbers begin to approach zero. According to relativity, mass can never move through the Universe at light speed. Mass will increase to infinity, and the amount of energy required to move it any faster will also be infinite. But for light itself, which is already moving at light speed… You guessed it, the reach zero and zero time.

Photons can take hundreds of thousands of years to travel from the core of the Sun until they reach the surface and fly off into space. And yet, that final journey, that could take it billions of light years across space, was no different from jumping from atom to atom.

Explore further: Can light orbit a black hole?

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markheim
4.1 / 5 (15) May 08, 2014
This should not be on phys.org. I come here for news.
Z99
4.3 / 5 (11) May 08, 2014
I hate to be the first to comment, since its gonna be pretty negative. Science for the masses - I'm all for it - as long as its well done. This particular episode is well produced but contains all sorts of wrong/misleading claims. The video is longer than the text (for some odd reason), and contains more groaners. 1st: MODERN Physics no longer considers the increase in energy as an object increases its speed (kinetic energy) to be an increase in mass. Mass is rest mass (or for systems of objects, intrinsic mass), this is a change in terminology rather than the Physics. The benefit of this approach is that mass is speed invariant, a property of an object regardless of its apparent motion. 2nd. Cain makes a mess concerning time and distance. What does it mean to "experience" distance? (especially for a rock or a photon?!) Obviously, nothing - its anthropomorphization gone wild. 3rd. He claims that a photon becomes part of an atom (in the Sun) as if it continues to exist. It doesn't.
jalmy
1 / 5 (8) May 08, 2014
Not only is it not news, but the fact that red shift occurs the further and thus older the light source is from earth signify s light does in fact experience time, distance, or both to some extent.
antialias_physorg
4.3 / 5 (8) May 08, 2014
From the point of view of someone travelling at c the entire universe is 2 dimensional.
Subejtively no time passes between launch and arrival. Distance is speed times time - and anything times zero is zero. This is especially freaky in the case of a photon travelling towards a destination that it might never reach as seen by an outside observer (e.g. due to inflation of the intervening space). even such infinite flight time is reduced to a subjective time of zero.

There's couple related freaky things about photons:
1) A photon has no past light cone. That means nothing can affect a photon en route (which I take to be a beautiful way to show that photons that meet must superpose rather than interact).
2) In the Minkowski diagram the photon worldlines are the border between causal and acausal regions. It makes sense to me that the carrier of causality should (by neceesity) itself be acausal.
Z99
5 / 5 (1) May 08, 2014
Its the Energy 'contained' in a photon which takes tens or hundreds of thousands of years to move from the Sun's Core to its Corona, not the photons. Assigning a single identity to a series of photons is an error in thinking. 4th. While its true that if you could accelerate at 1 g for 21 years (of your time), you could theoretically travel 1 billion light-years (relative to Earth), but this is impossible based on known physics. The amount of energy required for acceleration would be cosmologically enormous, impact with a single particle of dust would vaporize you (among other problems) plus you would be traveling at 99.99999999999+% of the speed of light at the end of this acceleration, it would require just as long (another 21 years) to slow down to a stop. 5th. Photons reach zero distance? This is another mash-up. It doesn't MEAN anything to be in the rest frame of a photon. Photons DO travel distances (relative to us), there is no way to measure anything relative to them.
Sean_W
1 / 5 (1) May 08, 2014
Could all things--even massive, slow-moving particles--be made of particles which do move at the speed of light (maybe for just short distances repeatedly)? It would seem that that would leave no time or space at the particle level.
Nik_2213
5 / 5 (3) May 08, 2014
{Sigh} I wish these 'explainers' weren't so 'dumbed down' that they're actually wrong...
julianpenrod
1 / 5 (8) May 08, 2014
To experience time, you need to have an inherent, regularly proceeding system and something that acts like a memory to verify that so much change has occurred in the inherent system. For example, a clock oscillating, and then, something keeping score of how many times it oscillates. Traditional "science" does not recognize any internal structure to the photon.
But, Maxwell's definition of light is a pair of mutually enhancing magnetic and electrostatic fields, the electrostatic field giving rise to the magnetic field, the magnetic field giving rise to the electrostatic field, the electrostatic field giving rise to the magnetic field that gives rise to the electrostatic field. It seems photons so have oscillating internal structures , another demonstration that "relativity" is a fraud.
julianpenrod
1 / 5 (7) May 08, 2014
To experience time, you need to have an inherent, regularly proceeding system and something that acts like a memory to verify that so much change has occurred in the inherent system. For example, a clock oscillating, and then, something keeping score of how many times it oscillates. Traditional "science" does not recognize any internal structure to the photon.
But, Maxwell's definition of light is a pair of mutually enhancing magnetic and electrostatic fields, the electrostatic field giving rise to the magnetic field, the magnetic field giving rise to the electrostatic field, the electrostatic field giving rise to the magnetic field that gives rise to the electrostatic field. It seems photons so have oscillating internal structures , another demonstration that "relativity" is a fraud.
mark_mnarkwynne
1.7 / 5 (6) May 08, 2014
"Light doesn't experience time"

given time is a human construct then I would agree. A silly piece of so called science. Pointless and pretentious, how people earn a living dreaming up what amounts to utter tripe is beyond me. Criminal waste of time money and education.

JIMBO
3.7 / 5 (3) May 08, 2014
Quite possibly The Stupidest article ever posted here.
barakn
3 / 5 (6) May 08, 2014
Pejico
May 08, 2014
This comment has been removed by a moderator.
pandora4real
2 / 5 (2) May 08, 2014
Anthropomorphizing every.little.thing to death may be pulling in the dumb shits that like to think they know something but you're driving the core that actually understands this stuff away. Fast.

And astronomy is THE WORST. Find me one- ONE- article where you can get through a whole opening graf without some blatant anthropomorphizing. Hey, the technique was invented to make difficult concepts more understandable. Modest proposal- when it makes the concept LESS understandable, you've jumped the shark.

Just stop it.
Dr_toad
May 08, 2014
This comment has been removed by a moderator.
Mimath224
1 / 5 (1) May 08, 2014
I am a layman and I'm not going to repeat what has already been posted, I agree that this article is less than useless...if that is possible ha! Just imagine that '...increase in mass...' the mind boggles. Either this might end up as a BH or such a mass would spread throughout...agh not even worth the thought.
Seriously, and fortunately, most layman might (should) have read Bondi, Bohm, Feynman (six easy/not so easy pieces) etc not forgetting Einstein, on SR and so would have already a fairly wide range of perspectives and put this article where it should be...in the bin
howhot2
5 / 5 (1) May 09, 2014
I love relativity! It's almost as fun as quantum mechanics. The one thing the guy said that is absolutely correct is that relativity can be a mind bender. The famous physicist John Wheeler once said, there is only one electron in the Universe and argued that it was the mass component of the photon, and at the speed of light, it would be everywhere at once. He was just speculating for fun about the idea, but that was a great conversation.

From the perspective of a photon, Time = 0, Length = 0, Mass = 0, so it can be everywhere at once and therefore only one photon exists. Photons are Bose particles with integer spin so they are allowed to occupy the same space (of zero distance), so there are infinite number of photons all occupying a universe of zero time, zero space, and zero mass, but oddly non-zero energy (or information).

When I think of an infinity of photons linked to electrons orbiting a nucleus and quantum mechanics, where an electron jumps up or falls in energy. WOW!
nonenotone
not rated yet May 09, 2014
AmritSorli
3 / 5 (4) May 09, 2014
Time is a numerical order of photon motion in a timeless space.

http://phys.org/s...li+amrit
swordsman
3 / 5 (4) May 09, 2014
Obviously, no one understands physics. I suggest that you all go back and study Planck's theory as he wrote it: "Planck's Columbia Lectures -The Original Quantum Radiation Theory as Described by the World's Greatest Practical Scientific Theorist", 2005 a book by Dr. Weldon Vlasak who spent a full year in studying Planck's writing. Planck derived many of the laws of physics using just two equations! That is a feat that had never before (nor ever after) been achieved. Today's physics is obviously all mixed, with nobody seemingly understanding anything, but achieving "great" results in their opinions. Disagree with them and you are an outcast.
charlimopps
5 / 5 (1) May 09, 2014
What happens to the light when it passes through a medium that is not vacuum? ;-)
rockwolf1000
5 / 5 (2) May 09, 2014
This should not be on phys.org. I come here for news.


Maybe so, but it did generate an interesting discussion thus it does have some value.
Mayday
4 / 5 (1) May 09, 2014
Photons don't experience time?!? Worse yet, and perhaps the height of irony, photons are also blind! Blind as a bat, I swear.
Burnerjack
5 / 5 (1) May 10, 2014
"Light doesn't experience time"

given time is a human construct then I would agree. A silly piece of so called science. Pointless and pretentious, how people earn a living dreaming up what amounts to utter tripe is beyond me. Criminal waste of time money and education.
"Good work when you can get it." Beats my job, I'm sure!


Shootist
not rated yet May 11, 2014
Indeed
lamer_jason
1 / 5 (1) May 11, 2014
Since we have artificially been able to slow photons down a significant amount, have we created (subjectively) the oldest light in the universe?
antialias_physorg
not rated yet May 12, 2014
Since we have artificially been able to slow photons down a significant amount,

Slowing light down (or "stopping" it) happens via absorption-reemission events.

From the perspective of a photon, Time = 0, Length = 0, Mass = 0, so it can be everywhere at once

Only along a 1D line. It does have a direction.
therefore only one photon exists

Where do you get that from?

And photons are products of other processes. There are not inifinitely many of them.
gerabene
not rated yet May 12, 2014
I'm curious about your responses article below. Thanks!

What does time and space mean?
Time and space are inseparable. Time is required for space to exist just as space is required for a place or a thing to exist. Therefore, everything that exists within time and space is real to man. This is the truth about time and space to man.

In ancient days in-depth discussions about life and everything that exists took place in time and space and in a place that could be visited. Spoken human words in ancient days and even to this day are made up of sound-waves of human breath in time and space. Human breath is made up of nitrogen, oxygen, water vapour and many constituents, the nature of all of which is atoms, sub-atomic particles and energy, which are basically light. Just as lightning in the sky, which the human eye can see, transforms into thunder, light in the human breath, which the human eye .... read further,
http://www.acadun...ce_mean/
Whydening Gyre
5 / 5 (1) May 12, 2014
What happens to the light when it passes through a medium that is not vacuum? ;-)

some is absorbed and re-emitted. which cause further absorptions and re-emissions. Next thing ya know - all that absorption an re-emission have slowed light (energy) to a point of coalescing into - MATTER!
Not rocket science. Sheesh...
swordsman
1 / 5 (1) May 12, 2014
This is the problem with the Einstein-Minkowski relationship, which is highly flawed. It is all based on the concept of spherical radiation, which I have shown to be incorrect. All radiation is transverse in nature, and the actual measurements of antenna radiation show it quite clearly. Electromagnetic engineers didn't both to relate time phase with the radiation pattern, and physicists never bothered with it. See www.science-site/RadiationArticle.pdf to see the actual radiation pattern. It was presented at the IEEE Antennas and Propagation Society International Symposium 2003. If you look clearly, you will see the Einstein-Minkowski equation in the eigenvalue of the eigenvector in the antenna equation.
TimLong2001
1 / 5 (2) May 12, 2014
Sorry, but this is total BS. (BTW, I have previously proposed a 1 g. acceleration with a rotation of a spacecraft to 1 g. deceleration at the midpoint of a space mission in order to provide artificial gravity.) The time dilation usually referred to in special relativity actually has to do with the rate of reception of information as an observer approaches the speed of light when traveling toward the outgoing beam. As the observer approaches the beam, the rate of the information reception would increase as the approaching observer's velocity increases: "time speeds up". If an observer's velocity could increase beyond c, then the rate of reception of the information content would decrease with increasing velocity: "time slows down". Time would not actually speed up or slow down -- only the rate of information reception.
TimLong2001
1 / 5 (1) May 12, 2014
Also the Wheeler-DeWitt Eqation, where time drops out altogether, could refer to time actually being a metric that describes the relative positions of particles due to charge interactions resulting in rotations (initially at the sub-quantal level). The Now would be viewed as the "current state of the universe", with Past being a record of previous states and the Future being a projection based on initial states. Einstein's original postulation of 'spacetime' could actually be his recognition that time is created by these motions in space, with further elaborations by others eventually taking president, i.e. Minkowski's Block Universe, etc. NOTE: Space limitations prevented this point in my first comment: With the observer traveling at c, it would result in "time standing still" (no new information reception).
antialias_physorg
not rated yet May 12, 2014
What does time and space mean?

I guess that is one for the philosophers.
Time is required for space to exist just as space is required for a place or a thing to exist.

Careful. The word 'exist' already presupposes time and space. Deriving from that an interdependence of space and time is tautological.
TimLong2001
1 / 5 (1) May 12, 2014
I apologize for the multiple posts, due to space limitations. (That's why I don't Twitter. LOL) Adressing the restrictions of velocities to a "speed limit of c", we should actually consider this as the characteristic velocity of radiation. The assumed limitation is the reason for the conventional view of a light speed limit, but the dilation equations could better represent the information reception view of time dilation expressed in my comments above. The photon has been shown to have a vanishingly small mass (see "The Mass
of the Photon," by Alfred Goldhaber and Michael Nieto in the May 1976 issue of Scientific American.) This mass dictates a loss of energy in the photon resulting in a red shift. Hubble's initial proposal gave no indication of "expansion", which was based on the theory of Georges Lemaitre, a Belgium priest/physicist who tried to create a biblically consistent interpretation of red shift data (see http://www.photon...ng.html)
jalmy
not rated yet May 12, 2014
You should have said "This mass dictates a loss of energy in the photon OVER TIME resulting in a red shift. Which is exactly what I said. The simple fact that you cant even define red-shift correctly without mentioning either "over-time" or "over-distance" tells you that the light is being affected by one or both. Webster has several definitions of the word experience, I think this one fits best. "the act or process of directly perceiving events or reality". Does light experience time? Yes. Yes in fact it does.
Codeofuniverse
not rated yet May 12, 2014
Time is immortal while light is mortal. light can be seen in presence of time but time can not be seen in presence of light...
OdinsAcolyte
not rated yet May 13, 2014
Every theory comes from ideas. From pipe dreams. All of them.
No. A photon does not experience time. It is always now.
gerabene
not rated yet May 14, 2014
antialias_physorg,

It is written to make time and space to be understood clearly what they both are. Please read the entire text and then you would realise the tautology.