Constants in physics are funny sometimes. Not all constants of physics are like this, and the physics of it are a bit beyond me, but something like c acts more like a unit conversion factor between metres and seconds than an actual physical constant. The same interactions mediated by protons and electrons exchanging virtual photons give a meter stick its length and an atomic clock its frequency, and it is hard to define a changing speed of light that doesn’t act as if all you did was redefine your units, with either the stick changing its length or the clock changing its frequency and light ending up taking the same number of ticks of the clock to travel from one end of the stick to the other it always did.
2 Likes
the total sum of matter in the cosmos.
Isn’t it… 1?
3 Likes
Not pedantry at all. Dark energy wasn’t “discovered” in the '90s, perhaps “theorized” or “proposed” would have been better words.
7 Likes
10 Likes
8 Likes
Dark matter and dark energy are the phlogiston and invisible ether of modern physics.
2 Likes
I don’t think that analogy holds, really. There’s a huge amount of data to support dark matter being something real, unlike aether, which was literally a wild guess based on small scale observations. In fact there’s been attempts to directly image dark matter that have been moderately successful.
Dark energy is more like a constant in the math right now, but it is also definitely something because the observations of its effects are difficult to refute.
Those early Newtonian fudges were based on an absence of information about cosmology. Dark matter and energy come from information about cosmology.
9 Likes
We had one in Northern California called Rotten Robbie convenience store, I saw some sh!t go down there that I will never be able to rectify.
1 Like
The expansion rate of the universe was predicted to be slower than what Hubble actually sees.
I am holding my breath with anticipation to see what the JWST adds to this discussion.
2 Likes
“There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened.” -
13 Likes
Lol - I used to regularly fuel up at the Rotton Robbie in Alamo. That was the classy one!
1 Like
- The answer is always 42.
9 Likes
Perhaps the experiment is over and ‘they’re’ pulling the plug on the simulation.
TBH, that would be something of a relief…
2 Likes
“There is only a one-in-a-million chance astronomers are wrong”
- NASA
“Scientists have calculated that the chances of something so patently absurd actually existing are millions to one. But magicians have calculated that million-to-one chances crop up nine times out of ten.”
- Terry Pratchett
6 Likes
I always enjoy your posts, VeronicaConnor, on almost any subject. Thanks for the quick lesson on the difference between DE and DM.
I have a question I’ve never seen asked or answered: when we look through telescopes, we’re looking not only “back” into space, but back in time. I get that. What I don’t understand is how matter, like, say the Earth, got to where it is now faster than the light from distant objects did. IOW, how is it that we can see light from objects that left them hundreds of millions of years ago? Wouldn’t that light already have passed this point in space? I’m sure I’m misunderstanding the very nature of what “space” is topologically, but I just can’t wrap my mind around the idea that matter expanded into whatever “space” is faster than the light from observable distant objects like quasars – which, presumably, are long dead and gone. What am I missing?
1 Like
I’m not sure I understand the question. Distant objects are emitting lots light, and the photons we see are the ones that were emitted how ever many million years ago. However they’ve been emitting continuously all the time. What you describe sounds like a paradox only if there’s a single “batch” of light emitted at each object’s creation moment, or at its arrival at current position?
1 Like
I guess I’m trying to figure out how (for instance) the Earth “got here” before that old light did. I wish I were better at framing the question. Let’s see … 14 or so billion years ago, the Big Bang happened. Matter was thrust outward from the initial point. Objects like quasars started emitting light in the early history of the universe closer to that point of origin. Since then, they, and early stars and galaxies have burned out and quit emitting light. Our sun and Earth formed many billions of years later, farther out as the universe expanded. The matter that formed them got here traveling slower than light. So why didn’t that quasar/early star light outpace the slower-than-light expansion of matter that formed our solar system? That’s the best way I can come up with to describe my question. It’s a question that makes me feel profound and profoundly dumb at the same time. 
1 Like
When I was 5 my teacher asked everyone in class what they wanted to be when they grew up, I said “cosmologist” and got this exact reaction.
how do they know?
For the most part, we don’t, but they seem to be, and the assumption is extremely useful and reliable in almost all circumstances. Some of them are dimensionless or definitional or purely mathematical, mostly the rest are apparent relationships between things we can measure and have measured. But they’re always subject to change in response to new evidence.
I guess I’m trying to figure out how (for instance) the Earth “got here” before that old light did.
Your question seems to assume that the problem is objects moving away from a central point, and each other, as in “moving through space” the way you would move if I strapped a rocket to you. This is not what’s happening. What’s happening is that space itself is expanding over time.
Right now, if you’re one light year away, any light you send at me reaches me one year later. If you then start moving away from me (getting further across the Milky Way) that doesn’t matter, the light you emitted when one light year away still gets to me one year later. In this context your intuition would be correct.
But that 14 billion year old quasar isn’t moving, it’s at rest. And the Earth isn’t moving (well, it is relative to the sun and the milky way, but not much on a cosmic scale). But the space itself between the Earth and the quasar is bigger than it used to be.
One of the usual metaphors that you can visualize is a balloon being gradually blown up. Imagine Earth and the Quasar are two points on opposite sides of the balloon. A photon is a bug crawling across the balloon’s surface at constant speed. The expansion means it’s going to take a lot longer than you might initially expect for it to get from one point to another, because the amount of balloon is has to walk over is constantly increasing. And if the balloon is expanding fast enough, the two points might be getting farther apart so quickly that the bug never makes it.
It’s because we’re talking about expansion-of-space and not movement-through-space that this is a thing. Movement-through-space is always slower than light. That rule doesn’t apply to expansion-of-space. The expansion is locally slow. If I’m doing my conversions correctly, it’s about 0.5cm per year per lightyear of separation. So for anything enough billions of lightyears away from Earth, the distance between us and it is increasing faster than c, so that light it emits today can never reach us. For anything just under that limit (say 5 billion light years), the distance is increase at almost-c, so that the light it emits today will take way longer than 5 billion years to reach us (or maybe never, if the expansion keeps accelerating).
8 Likes
That’s a good explanation, and I get the balloon and ant analogy. In fact, that makes me remember reading in a book many, many years ago that the space we live in is the skin of the balloon, not the inside volume of the balloon (and then it went on to talk about theoretical wormholes through the inside volume). However, you’re telling me that the expansion of space itself exceeds the speed of light? That is something I’ve never read before. If that’s indeed the case, then it all makes sense to me now as you’ve explained it. Thanks for taking the time to respond to a curious and humble illustrator.
2 Likes
