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Comment by lmilcin | Hacker News Reader

And... another author that doesn't get it or looks for a controversial, clickbaity title.

The correct way to state it would be to say: "We are seing things that are currently 46B light years away but since they are so far away we see them as they were 13.8B years ago when they were much closer than they are now."

I see absolutely nothing difficult about that statement unless you really need to create some piece of content and you figured out you will make something difficult so that you can then make it a little bit easier and be a hero.

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Yet you can't account for them now being 46B light years away without breaching C, or encompassing the expansion of the universe, within which things are moving. I think he manages a clear explanation of that without scaring away too many.

Your "correct" version on the other hand, leaves more questions than answers, not least of which being how do we ever get 46B ly distance in something 13.8B years old. Then you have to cover the expansion, relativity, and hey presto you've written the article. Just skimming the other comments here makes it clear it's not a topic that's well understood or intuitive.

Clickbait it ain't, and the title is a very fair question.

I'm really disappointed to see this the top voted HN answer right now...

Right - It is not clear how we can see something more than 13.8B ly away since it would take more than 13.8B years for signals of its existence to reach us. From our frame of reference, that would mean the emission started before the big bang.

This was described almost hundred years ago.

https://en.wikipedia.org/wiki/Hubble%27s_law

"(...) the notion of the universe expanding at a calculable rate was first derived from the general relativity equations in 1922 by Alexander Friedmann"

The space expands. It's been known for a long time.

We might not know why exactly this happens and there is still some discussion about ultimate fate of the universe although prevalent theory is that it will expand at an ever faster rate until every molecule will be torn from each other and matter will no longer be able to form.

Great, now you’ve started to touch on the points mentioned in the article.

Sure, but the high school, pop science and TV explanations of relativity and the universe rarely consider anything apart from the two trains travelling toward each other, nearing C, with an observer aboard one train. People can grasp that relatively easily, along with doppler explanations of red shift. Every decent attempt to take a step or two further is to be approved. :)

When tracks start moving as well it gets mind bending, and no longer intuitive. Now we have multiple scenarios where the combination of track movement (universe expansion), and train movement result in it being "obvious" you have to exceed C somewhere, which we're told is impossible. Otherwise how can the distances end up where they are. It's between these two points most non-physicists stop as it starts to feel deeply contradictory.

Your dismissal underestimates the qualifications and pedigree of an established and excellent populariser of "cool" scientific topics.

Sure he goes for clickbaity articles now and then, but he's pretty good at them in my experience, and your summary is both incorrect (there is no "current" over that distance scale) and leaves all explanation out.

It’s about as wrong as looking out a window and claiming the earth is flat “because it’s easier to imagine.” Just as dangerous, too...

It's at lesst a little confusing how something went from 14B light years away to 46B light years away (seems to be a distance of 32B light years total travel) in 14B years.

It's called "mathemagick".

No, the universe is expanding. No magic required.

Infinite amount of dark mathemagic is required for faster than light expansion of nothing.

Not really.

FTL speed requires infinite amount of energy in this iteration of physics, except for case when vacuum is not empty, but even in this case medium cannot move at supersonic speed of medium, while still in one piece. If far away vacuum moves at FTL speed, then there must be "sonic" barrier somewhere.

It's the fabric of spacetime that's expanding. Nothing physical is moving and thus no energy is necessary.

You aren't stationary and space itself is expanding.

The metaphor I normally see is a balloon being blown up.

Importantly, the expansion of the universe is necessary. Under special relativity two things could be moving at .9c toward one another and their velocities won’t somehow add to 1.8c in relative velocity. Light will still travel at c from one to the other.

Except the galaxies do not travel. Galaxies are more or less stationary, it's the space inbetween that expands. Think in terms of raisins in a dough or points on expanding baloon. Neither of them could be said to travel, yet they can be seen to become more and more far away.

No, space inbetween is stationary. It's galaxies that shrinks. Think of ice in water.

What’s the difference, observationally?

Shrinking releases energy. Expanding consumes energy.

Energy from where?

and yet you stated nothing about this factor in your original comment.

Technically, galaxies do travel:

> In physical cosmology, peculiar velocity refers to the components of a galaxy's velocity that deviate from the Hubble flow. ....

> Galaxies are not distributed evenly throughout observable space, but are typically found in groups or clusters, where they have a significant gravitational effect on each other. Velocity dispersions of galaxies arising from this gravitational attraction are usually in the hundreds of kilometers per second, but they can rise to over 1000 km/s in rich clusters.

-- https://en.wikipedia.org/wiki/Peculiar_velocity

Granted, 1000 km/s isn't even 1% of light speed, so clearly this motion couldn't contribute much to a distant object's recession.

That's why I wrote "more or less stationary", which is describing 1000km/s compared to double the speed of light that would come from naive calculation.

Ah, fair enough. I glossed right over that qualification, which is not a smart thing to do on HN--a credit to the quality of discourse here :)

your explanation would naturally raise the question why the difference. you can't really explain it without mentioning the expansion of the universe

I personally prefer to avoid saying "currently" for far away objects, because I don't understand it. Only what's in our light cone.

There’s a huge difference between click bait and this. Click bait makes a crazy claim anyone would want to click on, “click here to learn the secret of immortality”, and delivers something mundane with little connection like “antioxidants are good.” This is choosing a compelling title for a topic or concept that otherwise might be a little boring or otherwise get viewer clicks - aka, marketing.

The way you state it pretty blatantly leaves the question of "if they're 46B light years away, then how is the universe not at least that old?".

This comment heavily reminds me of the mannerisms of professors that have the mentality of "I deeply understand this subject from years of past studies, so you should be able to understand it from my vague and half assed explanation alone".

It's a pop science article, and I'm sure the audience that's into pop science articles found it interesting and probably learned something. I'm not really sure what you expect.

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