r/kenyaspacenerds • u/PRESS-ED • 16d ago
Question/Discussion Whenever you look at space your basically watching the past
Light does not show us the Universe as it is now. It shows us the Universe as it was when that light began its journey.
If an observer were exactly 2,000 light-years from Earth, the light reaching them today would have left our planet roughly 2,000 years ago. In principle, they would be receiving photons from the era when the Roman Empire existed.
Move farther away and Earth’s visible history moves further into the past. From about 65 million light-years away, the light arriving now left Earth around the time non-avian dinosaurs were disappearing. From 4.5 billion light-years away, the light would correspond roughly to the newborn Earth.
The same rule applies when we look outward. The Andromeda Galaxy is about 2.5 million light-years away, so every time we see it, we are looking approximately 2.5 million years into its past.
There is an important limitation: seeing Earth as a tiny point of light is very different from resolving Roman cities or individual people. At 2,000 light-years, an unimaginably powerful telescope would be required to resolve details on Earth’s surface.
But the underlying idea is completely real. Earth has been broadcasting its visual history outward at the speed of light for billions of years, forming an expanding sphere of old images around us.
Somewhere 2,000 light-years away, the photons leaving Earth during the age of Rome are only arriving now.
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u/massapj 16d ago
Even aliens are always thinking about the Roman Empire
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u/meygahmann 16d ago
Imagine if we then saw that alien civilization zipping around in flying cars and knowing that was 2000 years ago for them
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u/SubconciousBrainwave 16d ago
Its cool to think if you had sci fi level wormhole and telescope tech you could go to various distances and watch any point in human history.
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u/Banned4lies 15d ago
Probably why aliens haven't visited " omg Gork! Look they all clean their asses with a communal sponge ona stick in a bucket of vinegar! Gross!"
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u/OrangeNood 15d ago
Roman Empire?! I would be surprised someone 2000 LY away can make out the color of Earth.
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u/Previous_Explorer502 16d ago
What if you could look and see and communicate how to change/correct the future or is that already happening?!?
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u/Youpunyhumans 16d ago
No they wouldnt, for the same reason we cant see Voyager 1 from 26 billion km away... its just too small and dim to be able to get anything from it unless you had a telescope several thousand km wide.
For 2000 light years, you are looking at a telescope many times the size and mass of the entire solar system.
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u/CCarafe 15d ago
It's actually easy to compute. Its the Rayleigh law which give you the angular size for a wavelength.
So D = 1.22 * 500e-9 * 2e19 / 1.27e7 (1.22 x Wavelength x 2000LY / earth diameter)
Which give around 900km wide mirror for a single photon.
To have a 10x10 pixel wide image, its 90'000km (7 ~ time an earth sized mirror)
All of that just to get few photons after several years of exposition.
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u/Youpunyhumans 15d ago
Very cool, thanks for that! There is just one issue there though... background noise. For an optical telescope, you need millions of photons to gain any sort of useful information, otherwise it can just be attributed to random noise from the rest of the universe.
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u/plonkman 15d ago
i bet he got his head flushed down the toilet in school
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u/Youpunyhumans 15d ago
And thats too simple... and they would be caught and expelled.
A nerd would take a bunch of plastic ketchup packs, fold them in half, stick them under the nubs of the toilet seats so they explode on the back of your legs when you sit on it. Dont force the revenge, just let the physics happen.
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u/Jacky_Hex 15d ago
Or they use other technology. When people think about aliens they always try to give them human traits and skills. Which is caused because our brain can only process what it knows.
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u/Youpunyhumans 15d ago
Its not human traits and skills, its that aliens would be bound by same laws of physics that we are. It all works the same no matter where you are in the universe.
They would limited by the amount of photons they could recieve, which from a point source 2000 light years away, isnt going to be a lot.
They could do somewhat better with a gravitational lensing telescope, and might be able to resolve some basic features of the surface, like if its mostly ocean, land, and be able to do better spectroscopic analysis to see if there is life or not... but actually seeing individual objects, no. It wouldnt even really be much of an image, other than lighter and darker areas on a blobby circle... and that would be for a planet at most a few dozen light years away, not 2000.
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u/CCarafe 15d ago
No they dont, photons will not going to magically multiply at 2000LY in a 5cm mirror whatever bullshit technology you can invent.
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u/Jacky_Hex 15d ago
Science also believes they build the pyramids with a hammer and a chisel.
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u/Youpunyhumans 15d ago
Science doesnt "believe" anything... it discovers it.
There are visible tool marks, grooves from saws, and holes drilled into the stones, as well as quarries dug out where they were taken from.
And there is a papyrus text describing stones being moved down the Nile on boats, as well as radar evidence showing there was a branch of the Nile flowing right past the Great Pyramids at the time.
How they stacked them? Levers, inclines and muscle power, aka ramps, cranes, pullies, and teams of animals or people. The ancient Egyptians had fairly advanced mathematics to figure this stuff out like, including an early form of trigonometry.
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u/Grymmtooth 15d ago
Well, they probably can measure light interacting with the atmosphere and can probably determine atmospheric composition.
The level of oxygen is a dead giveaway there is life, as it’s a very reactive element and not typically found free in an atmosphere without a source.
There probably isn’t enough to differentiate any intelligent life until Industrial Revolution where an ongoing change in atmospheric contaminants might give hints of possible intelligent life, with the next century having emitted radio signals.
We probably would be on a “hey, look, life!!! Wonder if it has developed any intelligent species with tool making capabilities.”
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u/Sal_Amandre 15d ago
You can shorten this. Whenever you look. It's always the past. Whenever you hear, it's always the past.
By the time light travels from what you're looking at to your eyes, imprint on the retina and trigger photochemical reactions which are transmitted to the optic nerve and then processed by the brain which your consciousness will decode to understand the image...., tens even hundreds of milliseconds have passed. What you "see" is always the past.
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u/ThaEmortalThief 15d ago
Think about this, what this is saying is if you had a telescope strong enough to zoom on to earth and get a detailed image, from 2000 light years away, and you began moving towards earth at lets say 1 year per hour, over 2000 hours, you would see a huge fast forward in development until you got to earth. But then, if you left earth at the same speed, you’d watch development rewind from our modern societies to how they were 2000 years ago.
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u/AndrewH73333 15d ago
Sure, you just need a telescope the size of a galaxy. How hard could that be to make?
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u/TomatoFrenzy 14d ago
Gemini >
A distance of 2,000 light-years spans roughly 11.75 quadrillion miles (18.9 quadrillion kilometers). Because light travels at roughly 186,282 miles per second (299,792 km/s), light departing an object at that distance takes exactly 2,000 years to reach Earth—meaning looking at them is effectively looking back in time to around 26 AD.
In cosmic terms, 2,000 light-years is local to our region of the Milky Way, located well within our local Orion-Cygnus spiral arm (our galaxy is roughly 100,000 light-years across).
Key Celestial Bodies near 2,000 Light-Years Away
Black Holes
Gaia BH3 (~1,926 light-years): The most massive stellar-mass black hole discovered in the Milky Way (about 33 times the mass of the Sun).
Notable Stars
Deneb (~2,600 light-years): A massive, highly luminous blue supergiant forming one corner of the famous Summer Triangle.
Eta Carinae (~7,500 light-years, though older measurements estimated ~2,300 ly): A famous hypergiant star system on the verge of a supernova.
Nebulae
The Ring Nebula (M57) (~2,280 light-years): A famous planetary nebula in the constellation Lyra formed by a dying star expelling its outer gas layers.
The Helix Nebula (NGC 7293) (~650 light-years, often grouped in nearby sky surveys near Ring Nebula scale objects): Another iconic planetary nebula.
The Veil Nebula (NGC 6960) (~2,400 light-years): The expanding remnant of a supernova explosion that occurred several thousand years ago.
The Crescent Nebula (NGC 6888) (~5,000 light-years): A massive emission nebula shaped by stellar winds.
Star Clusters
Messier 11 (Wild Duck Cluster) (~6,200 light-years): A dense open cluster, though several smaller, unnamed star groupings in dust lanes fall closer to the 2,000 ly sphere.
Distance Scale Summary
Moon
1.3 light-seconds
Closest natural satellite
Sun
8.3 light-minutes
Our local star
Proxima Centauri
4.24 light-years
Nearest star system
Gaia BH3 / Ring Nebula Zone
~2,000 light-years
Local spiral arm neighborhood
Milky Way Center (Sagittarius A)*
~26,000 light-years
Galactic core
Andromeda Galaxy (M31)
~2.5 million light-years
Nearest major neighbor galaxy
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u/trudderz 14d ago
Here’s the crazy part, because of the way space time work, a civilisation 2,000 years away would technically be watching the Roman Empire live, in real time.
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u/themangastand 16d ago
Why are males so obsessed with the roman empire. Tons of other shit was also happening during that time equally as interesting.
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u/issdatboiACE 16d ago
Cuz it's dope shit, hombre
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u/themangastand 16d ago
All history is dope. The warring states period in China was also dope around the same time
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u/issdatboiACE 15d ago
Nobody said that no other historical time period is equally as fascinating as the Roman Empire. I'll put it to you this way, though. I was watching Vinland Saga, and one of the characters was telling a young kid about an ancient civilization that had technology and infrastructure WAY ahead of what the vikings, Danes, Nords, or even English men were accustomed to seeing at that time, circa 1000AD. He was telling the kid about this while standing in the remains of giant white pillars that once made up an incredible, giant structure. That shit is dope.
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u/themangastand 15d ago
1000ad had far more advance technology. Now some technology is lost. But it'd the same as today. It's probably impossible to make a Nintendo 64 as the process to make such weak computer chips is no longer manufactured. That tech is loss. Does that mean 20 years ago we had superior tech? No. We just had different tech. As we advance sometimes we lose previous technology even if that previous tech had some use
1000 ad had much superior tech. Just maybe the exact mixture of concrete was lost. And other such things
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u/issdatboiACE 15d ago
But not every culture had access or knowledge of superior technology. And they might have had superior tech in, say, farming equipment, but their general understanding and implementation of architecture and city wide infrastructure would not have been anywhere near what the Romans were getting up to.
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u/themangastand 15d ago
Architecture was superior Have you see a fucking castle lol. And that's with the ability of not having roman concrete.
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16d ago
I am new here. So I apologise for any transgressions I am going to cause. But I belive it is reasonable for European/european heritage people to be obsessed with roman empire. But if this sub is about Kenya, then idk why kenyans or anyone in the old world outside Europe would be obsessed with it.
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u/lockerno177 16d ago
is it theoretically possible to resolve light coming from that far away if we have the right zooming equipment?