If you could travel at the speed of light...

[Astro14]

Here's an article that addresses this. The key lies in the fact that while objects in space are moving away from each other, space itself is expanding at the same time.


Some may hit a pay wall.
https://www.forbes.com/sites/starts...d-how-can-we-see-46-billion-light-years-away/

Ed

Yeah. I was wondering the effect of expansion as you travel - didn’t realize it was that much of a factor, but there is still argument over the rate of expansion, and the flatness of space, so, I am still not buying the 90 billion number - too many variables that are still being argued over…

After all, if we are headed for a “Big Crunch” at the end of the universe, it will be coming back towards us as we journey outward.

 

[Astro14]

It's like a cruel joke. We can intuit that there are things out there, but can never directly observe them. And what we can see is being reduced all the time.

Wait. What?

All of Astronomy is direct observation.

And what we can see is constantly being expanded, through better telescopes - e.g. JWST.

Even Hubble dramatically improved our ability to observe and that was many decades ago.

Long baseline interferometry has greatly improved our ability to see in the radio spectrum, for example.

We see more all the time, not less.

 

[Vil_Riker]

It's like a cruel joke. We can intuit that there are things out there, but can never directly observe them. And what we can see is being reduced all the time.

To add insult to injury, time doesn't exist either.

 

[Vil_Riker]

Wait. What?

All of Astronomy is direct observation.

And what we can see is constantly being expanded, through better telescopes - e.g. JWST.

Even Hubble dramatically improved our ability to observe and that was many decades ago.

Long baseline interferometry has greatly improved our ability to see in the radio spectrum, for example.

We see more all the time, not less.

He said "see", not observe...

 

[Astro14]

To add insult to injury, time doesn't exist either.

What? Where do you guys get this stuff?

 

[Astro14]

He said "see", not observe...

Synonyms in the way I was using them.

 

[stormgol]

even the Milky Way is not alone in it's corner of the Cosmos. it is surrounded by tons of satellite Galaxies. so far we have discovered 61. it is the same for Andromeda Galaxy. there is a lot of stuff to explore around the Milky Way.

https://en.wikipedia.org/wiki/Satellite_galaxies_of_the_Milky_Way

https://en.wikipedia.org/wiki/List_of_Andromeda's_satellite_galaxies

 

[2strokeNorthstar]

And?

And it could all just be made up since it's impossible to actually know

 

[Astro14]

And it could all just be made up since it's impossible to actually know

Wait. What?

Where do you guys get this stuff??

Actually, there are a great many things in Astronomy that are known. Absolutely known. It’s not “made up”.

For example - the curvature of space time was proven in the 1950s by the occultation of Mercury. Newtonian mechanics predicted one thing, Relativity another, and the measurement exactly aligned with the prediction of Relativity.

Not made up.

Proven.

 

[Astro_Guy]

The time taken to reach a speed very close to the speed of light, such as 99.9%
of C at a constant proper acceleration of 3G is approximately 3.423 years from the perspective of the traveler.

So in other words if you are planning to tavel at light speed without ending up like a bug on a windshield then you had better plan on a seven year trip. And just forget about stopping to change your oil - LOL.

 

[jghall00]

Wait. What?

All of Astronomy is direct observation.

Not really. Do directly observe dark matter? Do we directly observe gravity? There's a horizon beyond which light from distant objects simply can't reach us. When an object crosses that boundary, it's no longer visible, but that doesn't mean it just disappeared from existence. That's what I was referring to when I said there are what we can see is being reduced...objects that have passed beyond the horizon at which their light can actually reach us.

 

[kschachn]

Not really. Do directly observe dark matter? Do we directly observe gravity? There's a horizon beyond which light from distant objects simply can't reach us. When an object crosses that boundary, it's no longer visible, but that doesn't mean it just disappeared from existence. That's what I was referring to when I said there are what we can see is being reduced...objects that have passed beyond the horizon at which their light can actually reach us.

On that one we do.

 

[StarCaller]

Is the universe infinite? Scientists reveal how vast it really is....

 

[jghall00]

On that one we do.

Not quite...we can see and measure the EFFECTS of gravity, but not gravity itself. We're still not even sure what its underlying mechanism is, graviton, or other. That's why dark energy is still a theory. We're observing gravitational effects, but it's entirely indirect because it's dark...we can't actually see it, just observe the effect it has on things around it.

 

[kschachn]

Not quite...we can see and measure the EFFECTS of gravity, but not gravity itself. We're still not even sure what its underlying mechanism is, graviton, or other. That's why dark energy is still a theory. We're observing gravitational effects, but it's entirely indirect because it's dark...we can't actually see it, just observe the effect it has on things around it.

No, we measure waves directly. It’s probably both particles and waves, but either way we are directly measuring it. It’s not an effect that’s being measured.

Unless you don’t believe we directly measure light?

 

[Astro14]

Not really. Do directly observe dark matter? Do we directly observe gravity? There's a horizon beyond which light from distant objects simply can't reach us. When an object crosses that boundary, it's no longer visible, but that doesn't mean it just disappeared from existence. That's what I was referring to when I said there are what we can see is being reduced...objects that have passed beyond the horizon at which their light can actually reach us.

That’s not actually how it works. Before you talk about the limits of knowing, you have to understand what we do know.

So no, dark matter is not directly observed, but its effects are - and to be honest, the name, dark matter is derived from the fact that there must be a mass, but it doesn’t emit light. This is still a very theoretical construct.

I don’t know what objects you’re talking about passing beyond what horizons, but we can see back to the beginning of the universe by examining the background radiation, and we can see 14 billion years into the past and 14 billion light years distant. There’s not a lot of matter that is “passing the horizon” except, perhaps, for the accretion discs around black holes, where matter crosses the event horizon, and which represents a really small amount of the universe, and which has negligible affect on our ability to understand what we do see.

 

[Jetronic]

Not sure I am buying all of that meme…

2,000 years to get out of a disc that is roughly 1,000 light years thick where we are? That’s off by a factor of 4 (it can’t be more than 500 light years to the “edge”) or a factor of 10 if you consider the dark matter halo.

And that last part of the meme - for a universe that is +/- 14 billion years old - it’s 14 billion light years observable in each direction, even accounting for early inflation. So, why the 90 billion years to go 14 billion light years? That’s off by a factor of 5, or more…

Maybe because it’s “The speed of ight”? Is that the same as the speed of light, or is it different?

I'd have a few breaks if going 500 lightyears distance. that'll add up....

 

[kschachn]

I don’t know what objects you’re talking about passing beyond what horizons, but we can see back to the beginning of the universe by examining the background radiation, and we can see 14 billion years into the past and 14 billion light years distant. There’s not a lot of matter that is “passing the horizon” except, perhaps, for the accretion discs around black holes, where matter crosses the event horizon, and which represents a really small amount of the universe, and which has negligible affect on our ability to understand what we do see.

There is a cosmological horizon since light does have a finite speed and the universe is expanding.

 

[Astro14]

There is a cosmological horizon since light does have a finite speed and the universe is expanding.

True, but it’s not accurate to say that objects are passing beyond it.

When we look that far away, we are looking that far back.

When we look to the horizon, we are seeing the beginning of the universe. We’re seeing the 2.7° Kelvin radiation.

So, no objects are going “past that horizon” to become “unobservable” because beyond that horizon, from our perspective, predates the Big Bang.

 

[kschachn]

True, but it’s not accurate to say that objects are passing beyond it.

When we look that far away, we are looking that far back.

When we look to the horizon, we are seeing the beginning of the universe. We’re seeing the 2.7° Kelvin radiation.

So, no objects are going “past that horizon” to become “unobservable” because beyond that horizon, from our perspective, predates the Big Bang.

True it goes the other way, we see more as time goes on.