If the universe is expanding, are we expanding too? | Hacker News Reader

If the universe is expanding, are we expanding too?

forbes.com

16 pointsautokill18 comments

Veritasium recently did a video on this

https://www.veritasium.com/videos/2020/10/23/do-you-expand-w...

TL;DR: No, we are not expanding. The phrase "expanding universe" is most attributed to the empiric evidence of red shift of the photons we see from outer space. But the red shift does not mean that the space fabric itself is expanding, it only means that photons and their frequencies are not simple local phenomena, they depend on relative aspects of space and observers. The frequency of a photon is not best seen as just the photon, it is more accurately described as source/photon/observer system.

The distant galaxies that are sending photons are indeed moving away relative to us as observers. But the atoms in the earth, and inside your body do not expand in the same way, and the space fabric/ether itself, "the grid of coordinates" that the earth sits in does not expand.

Did galaxies evolve much quicker billions of years ago since expansion hadn't yet pulled them as far apart? In other words, the further back in time you go did matter tend to interact much more frequently so in some sense the interaction-time of the universe is much longer than the actual number of years?

Between two charged particles (electric or maybe neutral particles by gravity) is some force. Moving them away will require energy. So e.g. you put two charged particles in this expanding space, the ongoing expansion will cause some energy which can be harvested? Can we build our "Zero point modul" which generates energy out of "nothing".

We dont even need particles for this effect since this is based on virtuell particles which ghostly appear and disappear (the Casimir effect)? Or maybe a proper medium would suit better (more particles more energy from expansion) e.g. the densest object like a black hole in this expanding space machine?

The simple answer is "No."

The more complicated answer is that empty space is expanding, but matter is not. Gravity, and matter subjected to the various forces, holds together even as empty space expands around it.

It's more complicated than that, if you want to read all the way to the end of the article.

The wild thing to me, assuming I understand it correctly, is that the expansion speed can exceed the speed of light.

Yep. That’s why we talk about the observable universe. Objects outside the radius of the observable universe are moving away from us so quickly that any light or gravitational effect from those objects have no chance of reaching us any longer.

You correct, but in the details. Travelling through space is limited to the speed of causality (the speed any massless particle travels) but space between itself is not limited to any particular speed.

Think of it this way: A balloon is space and the speed of sound is the limit at which waves can travel across it. This normal for sound waves. If every bit of the balloon expanded at 1 inch per second, a small balloon would be getting bigger, but wouldn't exceed the speed of sound. A sound wave will outrace the expansion.

Once the balloon as expanded to about 2500 feet in diameter, the expansion along the balloon will be greater than the speed of sound. A sound wave will never make to the other side. That said, no one place is expanding more than 1 inch per second. Nothing in part violates the speed of sound.

If you choose your relative objects that you compare carefully, even much simpler systems can be seen as expanding much quicker than the speed of light, relative to some specific theoretical observer.

But nothing can travel faster than the speed of light (no matter or energy or information), relative to the source point.

I just ate enough thai food for 3 people so I'm pretty sure I am at least

If it makes you feel any better according to relativity you're now slight more attractive.

I'm definitely expanding. Beer and Cheezits. Probably a minor gravitational anomaly at this point, but still.

Yes if we consider the universal as information and our relationships to it as receivers. We've been expanding our time experience for millennia and will continue to so as long we continue to imagine and create.

All organisms expand or grow. The universe is an organism. The earth is an organism. And it is growing. Etc.

The universe is not an organism in any accepted sense. It doesn't acquire energy from its environment, use that to reduce local entropy, and expel waste products. It is energy, it is expanding, and its entropy is reducing exactly in accord with thermodynamics.

If the universe is an organism, then so is my cup of tea!

Bacteria living in your body would make the same claims about you.

You are using the word "organism" in a very poetic metaphorical way. (And even then not a widely accepted one, but it being poetic, no one can really dispute it.) But the article talks about a very specific question in established physics which has already established terms and theories. It explains a valid question within that specific framework. In that framework talking about space as organism does not make a lot of sense, it doesn't add any new useful information.

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