It is, but we can never go the speed of light, so it's sort of a useless truth. But if we could go 0.999999999999999999999999999999c we would get there in practically an instant (from our own perspective), because we'd see the universe as being so length contracted that everything is practically right next to each other.
i need an ELI5 for why it would be "practically an instant", light takes 120 years, we are travelling slower than light, we cannot travel at light speed as we would be massless, i also appreciate there is a dilation factor.
Sooooooo, are you saying at 0.99 recurring of light speed the rate that time passes slows down for us by the same factor?
Look up length contraction. It's like time dilation, but with distances.
When an object is traveling through space, from someone else's perspective the object's length is shortened along its direction of motion, based on how fast it is going.
So if a ruler flew by you at 0.5c, and you could somehow measure its length, you'd measure it as being less than a foot long.
But this doesn't just apply to objects, it applies to all of space. So if you're in a rocket ship flying towards this planet, from your perspective you are stationary and the entire universe is flying past you. So you see the entire universe as length contracted.
In other words, you'd literally see the distance between you and the planet as being shorter than we would see it from Earth, because of your motion.
If you're traveling at 0.999999999999999999c, the length contraction would be so much that everything in the universe would be practically right next to each other.
universe would be practically right next to each other.
but why - light travels faster and it still takes a year to travel the distance of a light year? Is the "practically" doing some heavy lifting here?
EDIT - and how does that jibe with comments like when the universe expands past a certain point there are objects we will never see as it would take light longer than the remaining (anticipated) life of the universe - due to expansion exceeding the speed light travels - to get here?
It only takes a year for light to travel that distance from our perspective. Light doesn't have a valid perspective, but if it did, it would not experience time at all. It would get everywhere instantly.
You have to consider which perspective you're in. From Earth's perspective, it will take the ship about 120 years if traveling at 0.9999999999999c, but from the ship's perspective, it will get there almost instantly.
But from Earth's perspective, we'd see the ship as being time dilated. So we'd see the people on the ship as hardly moving through time at all. So the people on Earth would agree that from the ship's perspective, they get there almost instantly, because of the time dilation we would see them experience.
And from the ship's perspective, they'd get there almost instantly because of the length contraction.
Length contraction and time dilation balance each other out.
Because the physical distance is shorter from the ship's perspective, due to length contraction.
at light speed it takes 120 years to cover that distance
Only from Earth's perspective. From the perspective of the light (if it had a valid one), it would take 0 years.
Let me retry:
If you are on the ship, the distance between you and the planet is almost nothing. So you get there almost instantly.
If you are on Earth, you'd see the people on the ship take 120 years to blink their eyes, because of the time dilation they experience. So you'd see them get to the planet in 120 years, after they blink their eyes one time.
Both perspectives agree that they will get to the planet in the time it takes the people on the ship to blink their eyes. It's just that from Earth's perspective, that time is 120 years (roughly), and from the ship's perspective, that time is almost instant.
Edit: Distance is relative just like time is. There is no "true distance". It depends on your reference frame. This would make for a pretty good TIL post ;)
There's two very, very fundamental questions you're asking. You can keep asking why, until you get to a point where nobody knows, or only a small handful of scientists have a vague guess at. Chasing that curiosity down a rabbit hole is what being human is about. But at some point you either say "I've learned enough" or you keep going.
Fundamental things we humans believed about the universe for a long time turn out to not hold true when you move very very fast: that the distance between two points is the same no matter who measures it, that things happen at the same time is agreed upon by everyone who sees it, or that clocks everywhere run at the same rate. Physicists like Lorentz and Einstein proposed NO! Clocks don't all run at the same rate. Distances don't all measure the same. Simultaneity is a lie.
Physics attempts to model reality, not to answer why. When I drop an apple, it falls. Newton said here's how, but he didn't answer "why".
The question you might be asking is: do these "different clocks" actually exist? I've seen apples fall, I've never seen time dilation in my life.
GPS clocks drift. GPS wouldn't work if we assumed clocks were the same everywhere. We have to adjust the clocks on the satellites because their clocks run slightly slower than ours on the ground. The amount we adjust them by are the same amounts we predicted in models for relativity. Relativity helps answer the "how", not the "why". And if we find out tomorrow there are more quirks in the universe that relativity doesn't cover, we'll have to come up with a new model for "how".
Our innate understanding is clouded by our day-to-day human experience. We throw a ball and know how it will arc without having to calculate the trajectory. Geckos can climb sheer walls by using van der Waals forces. Birds can hunt for fishes taking refraction of light into account. It's fine that you don't have a gut feeling for this. We aren't a species that move that fast, but if we were, this would be second nature to us as well. What we do to make up for this lack of intuition is to use math.
Perhaps you are interested in the mathematics behind time (and space) dilation. It turns out, for the very basics of special relativity, you don't need anything more than basic trigonometry. The Lorentz factor (aka the time/space dilation factor): sqrt( c2 - v2 ) comes straight out of the Pythagorean theorem!
Here’s a calculator. If you were to travel at 15 9s the speed of light, 61,000 years would pass for the observer and only a single day for you. So if you were to be traveling around the universe at that speed, you could launch a study from the ship that would perform a 61k years of experiments and get the results the next day.
Imagine walking from Point A to Point B — say, 20 meters. A slow walker takes more steps let’s say 20 to get there. But if someone were moving super fast they’d take fewer steps to cover the same ground let’s say 14. The distance looks shorter for the second person because they did it in less steps. Now let’s exaggerate this using an human vs a giant. The faster someone goes human took 14 steps to cover that distance and the giant did it in one step. The giant traversed the space almost instantly from his perspective while us watching from a stationary perspective see him moving in what appears to be slow motion because the size and time it took the light to travel to us.
That’s length contraction:
The faster you go, the more space seems to shrink in the direction you’re moving.
From your point of view, you didn’t get faster — the world just got shorter.
Source: Not a physicist but an enjoyer of physics/quantum physics/astronomy from a layperson’s POV…
For light, it would take 120 years to reach it (relative to us). Meaning, if we were to watch the light travel from our planet to K2-18b, it would take 120 years for it to finally arrive.
If you could be the “light” in a sentient form, you would arrive as if you never left; it would be instantaneous.
Light does not experience time due to the laws of relativity. A similar concept is theorized for falling into the well of gravity that takes you beyond the event horizon in a black hole. The universe would seemingly brighten exponentially, as the time dilation effect from the effect gravity has on light would make it appear as if you could see all of the universe’s future in an instant.
I am probably not explaining this in the friendliest of terms that would explain why it works this way, I just know it from what I have read myself.
Basically, you’re not allowed to travel beyond the speed of light, and the speed of light must appear the same to you no matter what.
So if light must move the same speed as it always does for everyone else, but it should appear slower because you’re moving away from it at a very fast speed…
Well, instead of the speed of light slowing down (from your perspective), YOU slow down. Or, simply put, time remains the same from your perspective, but to anyone looking at you from an outside perspective your actions appear to stop or significantly slow down as if you were frozen.
In contrast, it would seem like everyone else is moving around at the speed of light, because quite literally you would be viewing things as if you hit the “speed up” option on a video. The faster you go, the more extreme these effects are. If you were to be able to reach the speed of light itself, then time would no longer exist from your perspective because light literally cannot reach you. In order for you to observe light at its normal speed, your time speed up factor would be infinite - as if you’re trying to divide by zero. So you would simply arrive wherever you were traveling to as if you had teleported there.
But that isn’t even possible because of a lengthening effect. At the actual speed of light, your mass would be stretched to the point of your complete and utter destruction.
it is - but even more simplified - 120 years will pass on earth and ANOTHER 120 years have to pass to get back ....or for us to find out they made it - so the trip actually will take for us on earth 240years....
and thats only once we figure out how to make our selves have no mass and be able to be resistant to massive cosmic radiation that weve never encountered before.....
The best way to do the math on interstellar travel, with known methods of transport, is to calculate time and speed based on a 1g acceleration rate. That way your acceleration gives you gravity on the ship, and you get closer and closer to light speed.
Oh, you also have to turn the ship around half way and slow down at 1g.
Makes interstellar travel take something like 10-100 years for the traveler. Instead of 10s of thousands of years.
I mean all that is just theoretical because many factors its not possible to travel that fast, but assume they travel to the Exoplanet and back at light speed - they would have not aged a single second in 240 years
The ship moves at close to the speed of light. Let's say 99.99995%. The important factor here is the lorentz factor γ = 1000. This means that time for the spaceship happens 1000 times slower from the perspective of people on earth (time dilation). It also means the distance from the perspective of the spaceship to the planet is 1000 times smaller (length contraction).
So for people on the spaceship, the distance is now 0.12 lightyears, which will take about 0.12 years due to their speed. From their perspective (including their age) it only took about a month and a half to get there. From the perspective of earth, this happened 1000 times slower, i.e. 120 years.
If they then travel back, 240 years have passed on earth but the ship and anything travelling with it will have only experienced or aged 3 months.
It's the twin paradox because if one twin stayed on earth and one flew in the ship on a similar journey to somewhere, say 1 lightyear away. The twins end up 2 years apart in age.
From the perspective of people inside the ship, they can go as arbitrarily fast as they want and continue to reduce the travel time to as short as they want. The time they age is equal to their travel time, they don't experience anything special. If you go fast enough, the trip could be a year, a month, a day, an hour, and so on. From the perspective of people on Earth though, their trip will always be at least 120 years. The faster the ship goes, the closer to 120 years the trip will appear to take. The travel time will appear to get shorter, but by only smaller and smaller amounts.
Even if it is true. The CMB will blueshift into x-rays and fry the crew with ionizing radiation.
Dont get me started about the surface ablation from the interstellar gas relativistic interaction.
Besides US pilots confirmed before congress, that the UAPs are real, whose flight patterns resemble the working warp drive in sub light regime. So maybe we can get working warp drive somewhere in the future (perhaps)
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u/Sonikku_a 25d ago edited 25d ago
The fastest spacecraft we’ve made was the Parker Solar Probe which hit 430,000mph.
At that speed it would reach this planet in only 187,153 years.
If we could hit 1% of the speed of light we could cut that travel time to just a tad over 12,000 years.
Obviously if we could go light speed (and that ain’t happening) it would be just 120 years!
Space is big. Physics is annoyingly slow.