Could dark energy be light itself?

We surmise that the universe is expanding due to the red shift of light from distant galaxies. It seems to have a roughly constant baseline everywhere. And there is some suggestion that we’re not looking at galaxies moving away from each other due to inertia so much as space itself expanding between them. But we don’t know what “dark” energy is creating new spaces between galaxies.

Well, there is an energy passing through those spaces: the very light we are looking at. What if the red shift is actually the sum of energy lost to the light that passes through space and the expansion of space due to energy from that light?

That would indicate that the universe is not expanding quite as fast as believed, but its expansion is a product of light passing through space.

Can we differentiate that from the present theory of spatial expansion?

I mean, can we show that the energy isn’t coming from the light itself?

I won’t understand the deep math, I just want to know if this has been brought up and disproven.

Dark Energy isn’t necessary for the Universe to be expanding. Its necessary to explain the acceleration expansion of the Universe, but people understood the more or less constant expansion many decades before anyone dreamed up dark energy.

I don’t know what “energy lost to the light that passes through space” means. The energy that is measured in observing red-shift is the energy of the photons themselves. I can’t really think of any way in which they “lose energy” to themselves.

I’m sure a more knowledgeable 'doper will be along soon, but my Science channel understanding of dark energy is that it’s effect that causes galaxies to repel each other…sort of an anti-gravity, or Einstein’s cosmological constant force. Light doesn’t have that effect. Nothing is known of it, afaik, and it’s never been detected…the only aspect of it that has been noted is the effect. More is known about dark matter, and even there it’s pretty much unknown.


So, dark energy is light energy, huh? :dubious:

Next up: “War is Peace”; “Freedom is Slavery”.

If light had that feature it should be pushing the Earth away from the Sun.

Do I dare?

It’s not constant; it’s accelerating. We have numerous lines of evidence for this, but the most convincing one is the supernovae observations in 1998 conducted by two separate independent teams of astronomers and verified thousands of times since.

“Dark Energy” is a media-created placeholder name. Scientists now use it out of habit and cultural pressure, but it doesn’t mean anything. All we know is that something is causing space to expand, and the media used the label “dark energy” because it sounds exciting.

This sentence, unfortunately, doesn’t mean anything. What does "red shift is the sum of the energy lost to the light" even mean? .

I realise that’s not the reply you’re looking for. The problem is, to answer a physics question, the question itself has to make sense. To an extent, that means you have to make the effort to understand the physics before you can ask sensible questions about it; otherwise you’re just parroting words you heard in the wrong order. A lot of the time, that means the stuff you hear in the media is - deliberately - dumbed dwn to the extent where they think you’ll understand it, but ends up giving you impressions via poor analogies and silly buzzwords which give you the wrong idea completely. When it comes down to it, the answer really is “the math says so”, and I totally understand that’s not intuitively satisfying, but that is the answer. The media’s explanations are erroneous attempts at creating an interesting narrative; they aren’t data you can use to draw any kind of conclusion.

That sounds harsh. I don’t mean to be. But, honestly, your question is nonsensical. To a physicist it sounds like “Is Adele popular in the charts because dolphins have non-Starsky & Hutch interior decoration preferences? Could that explain why Elvis died?” It’s just concepts strung together without reason. It’s not something anyone can posit an answer to.

Physicists do talk about the effect that photons have on the cosmos. They have energy and momentum, and so they create gravitational fields and influence spacetime in a similar way as “conventional” matter like protons and electrons do. If you have a bunch of photons travelling through space every which-way, you can even define an effective pressure that they exert: if you had some photons in a box whose inside surface was perfectly mirrored, they would exert a “kick” on the mirrors every time they bounced off, just like gas molecules do. So essentially, photons act like a gas filling space. Compared to “conventional” matter, they actually exert a huge amount of pressure for a given energy density.

The problem is that if we look at all the photons moving through space (mostly due to the cosmic microwave background), we find that the percentage of the total energy of the Universe that is due to photons currently is miniscule. The best figure we have right now is about 0.008% of the total energy density of the Universe — much much lower than that of “conventional” matter (about 5%), and way lower than “dark matter” (17%) or "dark energy (the rest.)

Moreover, photons act all wrong to be the source of dark energy. One of the weird properties that we think dark energy must have is that it has “negative pressure.” Photons have more conventional positive pressure (like a normal gas does). So the dark energy, whatever it is, has fundamentally different properties than light does as far as gravity goes. We don’t know much about it, but what few properties we’re sure about mean that it can’t be light.

I think you mean “Supertrain interiority complexes.” Easy mistake. :wink:

OK, let’s back up.

Red light has a lower energy than blue, yes?

The measurements of spatial expansion are based on observed red shift, yes? And not on counting millionths of a second of parallax?

The expansion of space is attributed to something called “dark energy” and when people say it appears to be a majority of the energy in the universe, they are using “energy” in a physics sense. Something’s driving this expansion, and the mechanism is wholly unknown, and maybe it’s not an energy, it’s “just an acceleration” like gravity–but it’s commonly regarded as energetic.

If I’ve got something backwards here, tell me.

Ah. You don’t think there’s an energy expended to make space expand? Or you don’t think the expansion of space counts as having energy?

But if it does, and the rest is correct, then:

Light energy at point of generation > light energy of the photon we see post red-shift.

Apparent expansion measured is a function of “red shift.” If light can (through some unknown mechanism) lose energy in some other way, we are overestimating the rate of expansion.

So observed “red shift” == loss of energy in transit + doppler effect.

What if there is actually a very small doppler effect from spatial expansion and most of the red shift is actually loss of energy into the spatial medium? What if space actually expands (very slightly) and absorbs light (very slightly) when light passes through it? Hence I ask, “What if the red shift == (is actually the sum of) energy lost to the light that passes through space + (and) the expansion of space due to energy from that light?”

This would mean that our measurements of spatial expansion are off by an unknown factor, and assumptions dependent on that don’t hold in this alternative model.

It sounds completely mad, but what doesn’t in theoretical physics?

Well, yes, but gravity is pulling us back in.

I know this model would require massively rebalancing estimates of spatial expansion, basic gravitational acceleration, etc.

I wonder if anyone has pursued this line of inquiry and disproven it. Can we tell it’s not the case?

I know, I know, Adele, dolphins, blah blah.

I think that what you’re trying to say is a version of the tired light mechanism.

This was one of the first stabs at explaining redshift, by Zwicky back in 1929. So it has a good pedigree. The problem is that it has been completely disproven by subsequent experiments. It’s so old that I suspect most people here don’t even remember it. Fortunately, I’m ancient. (And tired.)

Even if it were true, I doubt that it could be made to explain dark energy. That’s just a different class of phenomena.

Thank you!

Nitpick: While it’s true that the media likes to invent soundbite-friendly names (i.e. “The Big Bang”) this is not one of them. The term “dark energy” was coined by cosmologist Michael S. Turner.

Although it should also be mentioned that the energy density due to radiation falls off more quickly with the expansion of space than does the energy density due to matter. Thus, there was an era in the very early Universe when light was relevant to the energy density of the Universe, and even a time when it dominated over matter.

The energy density due to dark energy, meanwhile, doesn’t fall off at all as the Universe expands. Produce more space, and you also produce more dark energy to fill that space.

That sounds a lot like the Casimir effect. But that gets us into zero point energy and at that point we have to start distributing garlic and crucifixes - or whatever works on the perpetual motion folks. :cool:

edit: although there is this fascinating article in New Scientist.