How we are seen from a planet located 90 light years away

“Stardate 100669.9. Here’s a research team coming from the planet TOI-836b, a report from the third planet in the solar system We have just witnessed the birth of a man, a representative of at least, apparently, the most intelligent species in the observable world. We are requesting confirmation of the registration of an event from our home planet, 89.7 light-years apart between the two systems. We ensure that the basic directive has always been respected.”

Basic Directive

While we know that no extraterrestrial outposts have visited Earth, nothing stops us from fantasizing that it did. After all, the Starfleet Core Directive requires you to be careful at all costs not to reveal your presence or interfere with the history of visited worlds. Suppose they are here, but managed to ignore them.

Interstellar crew from TOI-836b claims to have witnessed on the spot the birth of a person on a star date corresponding to January 2023. But what did they see from that distant planet, if at that very moment, from afar, they were observing the Earth through a telescope?

Humans do not have the necessary technology to observe any world in space, even the moon, in sufficient detail to distinguish between individual people. But we assume that TOI-836b’s technology is very advanced, so let’s face it, they have an amazing telescope capable of such an optical feat.

They will watch their grandmother being born.

If in the planetary home of the expeditionary group they searched carefully here, it is possible that on the stardate 100669.9 they also witnessed the birth … but not of the one reported by the reconnaissance party, but of the grandmother of this baby. Indeed, with TOI-836b they see the Earth of the past, the one that was 89.7 years ago. They see a lucky day in May 1933, the date the baby’s grandmother was born, reported today by an interstellar expedition.

We perceive the cosmos through “messengers” that move at a finite speed, always equal to or less than the speed of light in a vacuum. One of these messengers, sound, the daily source of information for humans, travels so slowly that it sometimes surprises us with the consequences of this slowness, such as echoes or delays between lightning and thunder.

In astronomy, we have three main messengers. The first and most traditional is electromagnetic radiation, which includes light and propagates at the maximum speed allowed by physics, almost 300,000 kilometers per second. Second, we find gravitational radiation just as fast. And finally, we have neutrinos, which move a little slower because they have a small but non-zero rest mass. We could add a fourth messenger, cosmic rays, although less important than the three main ones.

light delay

No messenger can transmit information faster than the speed at which it spreads. In the case of light, this implies a delay of the same nature as mentioned above for the sound of thunder. But since electromagnetic radiation is much faster than sound, much longer distances are needed for any delay effect to be felt.

At a distance of more than 300,000 kilometers from Earth, it takes more than a second for the moon’s light to bridge the gap between our world and its natural satellite. American astronauts on the moon received radio signals from Houston with a delay that, although it may seem small, but caused some inconvenience in communications. Soviet pilots who remotely control the Lunokhod robotic vehicles also encountered this problem when controlling these all-terrain vehicles using remote control.

From the sun they’ll see us eight minutes later

Someone in the Sun will see what’s happening on Earth eight minutes too late. And the network of terrestrial robots inhabiting Mars “sees” what is happening on our planet many minutes later, up to twenty at the most: this is the interval that should be expected between sending an instruction from the command center and receiving it. surface. In another sense, the situation is symmetrical: when there is applause in the control room for the fact that the robot successfully landed on Mars, in fact, an event occurred in the past that could last several minutes.

The Voyager 1 probe took the famous image known as the “pale blue dot” on February 14, 1990 at 4:48 am (UTC). But at more than 6,000 million kilometers from Earth, what this probe recorded was not the reality of the moment of capture, but another, corresponding more than five and a half hours earlier, when it was still the 13th. This is the case from Earth, because Strictly speaking, each of the planets captured in this historical photograph was recorded at a different point in time, corresponding to the distance that then lay between each world and the space probe.

From a planet like TOI-836b, which is 89.66 light-years from Earth, they could only observe the birth of the baby’s grandmother in January 2023, and that’s with the right technology.

cell of light

Astronomy teaches us that we live in space inside a cell of light. We are taking over the universe with an inevitable delay due to the finite speed of the stellar messengers. With the naked eye, we see the stars in the sky as they were decades, sometimes centuries or millennia ago. From the closest large galaxy to ours, Andromeda, they can now see the Earth, where not a human baby is born, but an entire biological genus, a genus homo, the first representatives of which learned to walk along these edges about two million two hundred thousand years ago. The abyss of cosmic distances shows us at the same time the abyss of time towards the past as we look at more and more distant galaxies.

Sometimes this fact is perceived with some anxiety, with bewilderment and sadness caused by the realization that we will never know the real, “real” state of the most remote regions of space. But we must see our cage of light as a blessing, not a condemnation. Just because looking far is seeing the past, we have access to studying the regions of the universe as they were in abysmally ancient times. We even caught a glimpse of the afterglow left by the Big Bang just a few hundred thousand years after it all started.

If light traveled at infinite speed, then the instantaneous communication that floods sci-fi movies and TV shows would be viable. Style messaging Star Trek between a starfleet and their planet of origin could occur as described at the beginning of this article, and with TOI-836b they would witness the birth of a child in real time.

It is also possible that in star Wars, Obi-Wan Kenobi felt “a great disturbance in the force” at the very moment of the destruction of the planet Alderaan, despite being many light-years away (in fact, it would have taken him years, if not centuries, to find out). ). But apart from the consequences that this might have for the physics of the cosmos, infinitely fast light would prevent us from seeing the past of the universe and contrasting, through observation, theories about its origin and evolution. Doesn’t the inability to know one’s origin mean a far worse blindness than the one we suffer now, in this cell of light that turns a landscape into a photograph from the past?

David Galadi Henriquez, Resident Astronomer, Calar Alto Observatory, Andalusian Institute of Astrophysics (IAA-CSIC)

This article was originally published on The Conversation. Read the original.

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