Thinking about time is like viewing your footprints in sand. Look back and you can see where you've been, but look forward and there are no footprints because you haven't been there yet. Time travel to the past is possible, but the future isn't because it hasn't happened yet. You might think the past no longer exists either, but it actually does. Every aspect of now contains the past. The past is implicit in the present. The past exists in the present.
Is it possible to change the past? No. If you travel back in time and affect the past then you never actually changed anything. What you thought you changed was simply always that way; you just never realised it. None of the time paradoxes are really paradoxes at all. The timeline is perfectly safe from alteration, because you can't really change anything... which makes sense, because it has already happened. You can't kill Hitler because you already know he lived.
So what would you do if you could visit the past?
Ever since I was a child I knew what I wanted: to talk with Leonardo da Vinci and tell him how right he was, and how admired he will be for hundreds of years.
And that's what I did.
I learned the kind of French they were speaking in the early fifteen hundreds so that I could talk with him when I arrived. I know he was Italian, so why French? Because French was the universal language back then, and Leonardo spent his last years in the French countryside at Amboise. Also French is easier to learn. I did learn some old Italian too, though.
The clothes and footwear were more difficult. In the end I chose old styles, though as androgynous as possible — there was no way I was going to be impeded by the absurd dresses of that age. If I needed to explain my modern fabrics I say I came from far away. Covert pockets hidden under my garments carried some recent marvels of technology I wanted to show Leonardo. My purse only contained items that would be expected of a moderately wealthy woman of that time.
For safety, I materialised in mid 1517 at a small glade in the forest, not far from the manor house Clos Lucé, where Leonardo now lived. I looked around to ensure nobody had seen me. It was the Renaissance, but people were still very superstitious after more than a thousand years of religious indoctrination, and I could just as easily be killed here in the past as in the present.
Leonardo's house didn't look much different to how it does in the present, though the surroundings were completely different, of course.
His servant Battista answered my door knock, and brought me to an attractive middle-aged man, Leonardo's companion Salai, who greeted me, lifting my hand to his lips briefly. After listening to my explanation that I'd journeyed from far away to speak with Leonardo, he nodded. "He is writing. I don't think he'll mind being disturbed by a beautiful woman." He said this in a mix of French and Italian. My eyebrows lifted at being described as beautiful, but figured it was merely normal to flatter apparently wealthy women this way. Salai led me to the main workroom and my heart began to race. I was finally going to meet the person I admired most, and he would be in his element.
Salai gave a perfunctory rap on a door and entered, holding the door open for me to follow. He smirked as he announced that I was a wealthy woman who had come from far away to speak with the great Leonardo.
The room was a complete mess, stuffed full of papers, hundreds of books, bits and pieces of things, like pinecones, the skeleton of a frog, a bird's wing stretched out, with feathers still attached, next to it a bat's wing in a similar position. Paintings stacked, leaning against walls, leaves of various shapes on shelves, including several leaves which had decayed leaving only the delicate pattern of veins. Many dried animals and flowers were on cupboard shelves and side tables. Many of the cupboard doors couldn't be opened without moving great piles of stuff on the floor. There were trinkets, pieces of colored glass, curved pieces of metal, mostly bronze, cogs, and complex constructs of sticks and wires, and much, much more.
Leonardo and his other companion Francesco Melzi were seated at a large table where they'd been writing or drawing. Leonardo stood, pushing back his chair. At 64, Leonardo looked surprisingly well, considering I knew he was going to die of a stroke in another couple of years. He rounded the table and greeted me as Salai had, but without the flattery. "Madame, how may I be of service to you?" Like Salai, he used a mixture of French and Italian.
Francesco stayed seated where he was and looked completely uninterested in me.
"Thank you for meeting me, Leonardo. No, I want to do something for you."
The corner of Leonardo's mouth twitched. What could a woman do for him? Women were mere bearers of children in this period, and Leonardo was gay.
I said, "As Salai said, I come from far away — from beyond the Indies. But more than that; I am from more than five hundred years in the future."
Leonardo smiled skeptically and Salai chuckled. I noticed Francesco rolled his eyes.
Leonardo asked politely, "Am I to take your word for this?"
Grinning, I shook my head, reached inside my hidden pockets and brought out my tablet computer. I switched it on and held it out to him. Salai stepped over to stand beside Leonardo and look in surprise at the machine. Curiosity got the better of Francesco and he rounded the table to join them. I touched an icon on the screen to display the French Wikipedia page about Clos Lucé (I'd deleted the passages about his death from this copy of the page), then I scrolled down and back up with my finger. Leonardo caught on quickly and scrolled through it, avidly reading.
"How is this marvel created?" he asked.
"It is very complicated. The full explanation would take a long time, but this machine is powered by electricity — the same thing you see as lightning during a thunderstorm. This image is actually more than one and a half million tiny red, green, and blue dots."
Leonardo mumbled something to Francesco, who went back to the table opened a draw, and pulled out something small wrapped in cloth. Folding back the material revealed a palm-sized lens, which he presented to Leonardo, who took it and examined the screen for a long moment. He breathed a hushed exclamation, then asked, "Why only red, green, and blue?"
"Remember your studies of the eye? The eye's lens focusses light on retina at the back of the eye where there are enormous numbers of miniscule light sensitive... ummm nerve ends. Most of the eye's light detectors just respond to general brightness, but the yellow spot, the 'fovea'," I couldn't remember if that word described it in his day, "is packed with three kinds of light detectors — some respond to red light, some respond to green light, and some respond to blue."
He shook his head, "How do we see yellow then?"
"Red plus green."
Leonardo continued to squint through the lens at the screen, but Francesco shook his head and said in a tone of finality, "You are mistaken. Yellow is a primary color. If we mix red and green we get brown, not yellow. And green is a secondary color, gained by mixing yellow and blue."
Instead of answering, I said "Excusé," to Leonardo and scrolled the screen to the MediaWiki image at the bottom. Its emblem is a yellow flower. I pointed to it and asked Leonardo, "What colors do you see with the lens."
He frowned, then looked up, smiling, and handed the lens to Francesco who peered at it frowning and continued to frown after looking back at me.
I said, "Subtractive light works as you said because light shines through pigments, subtracting colors from white light, but additive light works the opposite way."
Leonardo pointed to a chair, "Sit. Tell me what the future is like."
I grinned. "Five hundred years later you are still considered the the greatest thinker and inventor and artist who ever lived. You were right about so many things. We use machines to fly faster than birds. We have helicopters, though somewhat different to your design. We can breathe underwater using equipment like you imagined. We have parachutes, very similar to what you invented. Whole fields of study have grown up around knowledge you explored.
"Your era ended the absolute rule of the church, and enabling genuine knowledge to grow and spread. We, in the future, understand more about the world than in your wildest dreams.
"Flight has reached a level that is difficult to explain. Huge machines, larger than this manor house, carry hundreds of people, flying faster than sound travels, thousands of leagues, in just a few hours. We have even built machines to carry some people to the Moon, where they have walked. But as there is no air there, they had to wear special suits and breathing equipment... like the underwater suits you designed."
I pointed to the tablet, "These machines, called 'computers', can store amazing amounts of knowledge, and not just text and pictures..." I tapped an icon for a music video in which a beautiful young woman sang while she walked through various scenes — a beach, a town, a city with tall skyscrapers, a forest, a mountaintop, a night scene where she danced with a young man while gleaming cars drove past along well-lit roads, an airport waiting lounge with an airplane taking off in the background, the view from inside a car speeding along a highway, and the singer alternately singing and passionately kissing another pretty young woman. There was a palm-lined esplanade and people rollerblading past laughing women dressed in bikinis...
Eventually the music video stopped and Leonardo looked at me, his eyes large and shining. "The future is paradise?"
I grimaced, "Not quite, but things do continue to get better. Violence and war are finally disappearing. People no longer are killed in duels," I couldn't help glancing at Salai who I knew would die that way some years hence. Salai didn't notice, but Leonardo did and his mouth tightened. "We still have superstition and religion, but both are shrinking. We still have poverty, but that is nearly eliminated. We have conquered almost all disease and most people expect to live healthily to one hundred years.
"Ignorance is declining. We have access to enormous amounts of knowledge — far more than any person could learn in their entire lifetime." I pointed at the tablet again, "This machine is smaller than most computers, but it contains more books than exist in all the world at your time. And we have a free encyclopedia, created and maintained co-operatively by thousands of people, available to everybody, and libraries where we can freely choose from many thousands of books. I can send a copy of a book to a friend who is thousands of leagues away and they will receive it almost instantly. Using this same device I can talk to and see my friend and they can see and hear me at the same time."
I reached out to the tablet screen and touched the camera icon. First the front camera view displayed, which I waved my hand in front of, then the selfie camera, showing the men's own faces. There was a chorus of gasps from them.
Leonardo smiled widely, "Wonderful! It is as I had hoped. No barriers to knowledge. Anybody can share what they have learned with anybody else at no cost."
I was uncomfortable. "Ummm... theoretically, yes. Unfortunately, our politicians have made laws to prevent people sharing knowledge."
Leonardo grunted and shook his head, "So there are still idiots in your time."
I smiled uneasily and nodded.
My timer suddenly started beeping. The time limit on my visit was almost expired, "I'm sorry, Leonardo. I can't stay longer."
He looked mildly panicked, "You must come again to tell me more. I want to understand how this works," holding up the tablet. He emphasised, "I need to know more."
"I'll try..." the cluttered room disappeared and I caught the tablet as it fell from vanished hands.