Why Are We Limited To Only Seeing The Past?

We are moving from A to B. Yet everywhere we look, we are going backwards! I mean the direction we are moving along [trajectory] must [?] have something in front of earth-solar system-galaxy. Yet it is all the past. No future! Now could this be because we are at the event horizon [so to speak] the very edge of the beginning? However one ‘material’ that has moved faster-than-light is space. Light is still catching up. Why can’t we see even this?
Our solar journey through space is carrying us through a cluster of very low density interstellar clouds. Right now the Sun is inside of a cloud (Local cloud) that is so tenuous that the interstellar gas detected by IBEX is as sparse as a handful of air stretched over a column that is hundreds of light years long. These clouds are identified by their motions, indicated in this graphic with blue arrows. Credit: NASA/Goddard/Adler/U. Chicago/Wesleyan

Our solar journey through space is carrying us through a cluster of very low density interstellar clouds. Right now the Sun is inside of a cloud (Local cloud) that is so tenuous that the interstellar gas detected by IBEX is as sparse as a handful of air stretched over a column that is hundreds of light years long. These clouds are identified by their motions, indicated in this graphic with blue arrows. Credit: NASA/Goddard/Adler/U. Chicago/Wesleyan

Originally posted on Forbes!

There’s a couple things blurring together here, but the fundamental thing here is the distinction between the observable universe and the universe which exists, independent of our ability to observe it.

You’ve got a good handle on the observable universe. This is the universe that we see, where everything away from our own planet has some kind of time lag to it. We see our Sun as it was eight minutes ago, in the past. We see Jupiter as it was, about 30 minutes ago in the past. We see the stars as they were, a few years to a few thousand years ago. We see the Andromeda galaxy as it was 2.5 million years ago. As we look farther out into the universe, and strain our technology to the limits, we push further and further back into time, capturing light which has traveled longer and longer stretches of time to reach us.

But because we can only see the universe as it was, some varying degree of delay later, doesn’t mean the universe is actually delayed the farther away from us we go. Mars is a few minutes away from us, but that doesn’t mean that Mars’s “now” is actually a few minutes behind our “now” – that few minutes’ delay is just the quickest any Mars-related information can get to us.

So space hasn’t really traveled faster than light to get “ahead” of our ability to see the Universe. Space describes what and where the universe is, and is not particularly concerned with how well we can observe it.

Think of it this way. We’re sort of walking down a road, but backwards. We can see all the things we’ve passed by, all of the pieces that we know about. Now, if the road is straight, and we know where the road is supposed to go, and where we are, we can pretty safely assume that walking backwards in a straight line will keep us walking along the roadside. We might be able to predict how long it will take us to get there, walking backwards. So it is with the universe. We can see where the universe has been, and we can roughly figure out what the rules are which govern its changes. So we can predict where we will go, and check our predictions.

So maybe the road has a bend in it. You might notice that near you, the shape of the curb is different from what it has been, and that will clue you that maybe, if you want to stay near the road, you should bend that direction as well. We can change our ideas of how this particular road goes, and similarly we can constantly check how well our models of the universe’s evolution predict what we should see, versus what we actually see.

This image shows New Horizons’ current position along its full planned trajectory. The green segment of the line shows where New Horizons has traveled since launch; the red indicates the spacecraft’s future path. Positions of stars with magnitude 12 or brighter are shown from this perspective, which is slightly above the orbital plane of the planets. Image credit: NASA/JHU

This image shows New Horizons’ current position along its full planned trajectory. The green segment of the line shows where New Horizons has traveled since launch; the red indicates the spacecraft’s future path. Positions of stars with magnitude 12 or brighter are shown from this perspective, which is slightly above the orbital plane of the planets. Image credit: NASA/JHU

We do this kind of prediction in all kinds of ways — we assume that the physics of the world around us are stable, so that when I step forward onto concrete, the concrete will still be there when I put weight on it, even though I can’t see into the future to check that it will be. Any kind of rover delivered to the surface of another world, or a spacecraft very carefully planned to swing past a planet, requires these predictions of what the space outside our range of sight will look like. And they work — New Horizons, arriving at Pluto, took only one minute less to travel there than was predicted in 2006, at the start of a ten year journey.

So while we’re not able to see into the future – the speed of light simply will never allow this – we’re not going totally blind into the future. From looking into the past, we have learned the direction our future is unspooling.

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