There is nothing in the universe that is human scaled.  Expansion is so fast at the edges that light cannot return from the far reaches of the universe.  Life has taken on different and truly extraordinary forms out there at the edge.

We are surrounded by paradox, move just a little and your time is not the same as someone else’s time, your centre of the universe is different, your signals will differ, your edge of the universe is different.

We don’t see civilisation when we look through telescopes because light is hopelessly slow, the extraordinary proliferation of life happens in recognisable forms, human sized forms later than we can see, because we can penetrate back to the beginning of the universe but we cannot see what is happening now.

Einstein showed us that the very concept of now is slippery.  And it’s slippery in so many ways.

By the time we have talked about now it is the past and yet for someone it is still the future.

Look at closest star, nothing that happens there will reach us for 4 years, (thereabouts).

This is profound, the universe has a speed limit, to understand it we need to scale it down.

When driving long distance, (I live in the UK), it doesn’t really matter how fast I drive the highest average speed I can achieve is about 60mph.  (It’s actually close to 50, but I want to make the sums easier later on and I can do better at night).  It’s as if the motorways were empty and I could still only do 60mph.  I can’t get anywhere faster than that.  It’s what I have to plan for.

The universe is like that, at 60mph I can’t anything about things until I get where I’m going.

If I have no remote communications; phones, telegraph, light signals, then I can literally do nothing until I get there.  (We’re leaving aside the minor difficulty that people might see me coming in the last few hundred yards).

That means that I can’t influence anything until I have arrived.

This is hard to wrap your head around, it seems simple, but it has consequences.

We talk about being a certain amount of time away from places, that’s familiar.  In our 60mph scenario if I’m two hours away then if I always travel at 60mph, (which for our scenario, I do), then I must be 100 miles away.

If something happens at your location and I’m two hours away then I can’t influence it for two hours, at all.

It’s worse than that though.  You’re thinking, “I can phone Friday and tell her that I’m in trouble.”  No, you can’t.  no phones, no light, no nothing.  You have to send someone.  They can travel at 60mph.  Your messenger takes two hours to reach me.  Until then I don’t even know you’re in trouble.  (In my scenario, you’re in trouble, because well, something happened).

Your messenger and I come back.  That takes another two hours.  Your messenger can’t communicate with you, so they and I only know what happened initially, that’s two hours ago when they reach me, and four hours ago by the time we reach you.

I hope you weren’t drowning.

The universe is exactly like that, (there is one exception, but it’s complicated and not really relevant here.  And Einstein didn’t like it.)

At 60mph top speed anything that happens 60 miles away cannot affect me for an hour.

We say that the maximum simultaneity between things happening “here” and things happening 60 miles away is an hour.  In our world, blow up a huge (atomic) bomb, and 60 miles from that event no effects will be felt at all, for an hour.  It’s as if, for that hour, that bomb hasn’t happened.

Actually, from the point of view of someone 60 miles away, it has not happened for an hour.

Nonsense, you’re saying, things that have happened stay happened.  True.  But let me demonstrate what I mean, and remember, if you’re at all knowledgeable about this stuff, I’m dealing with one tiny aspect of the real world because this part seems simple and people get to the weird stuff just too damn fast.

Anyhow I was saying that if we know what time that bomb is going off. (again, ignoring a lot of consequences about time and stuff that happen in the real world), and it’s more than an hour away, i.e. 60 miles, it hasn’t happened for us, and never needs to happen for us.

You should have a good idea by now that we can drive away from the centre of the blast.  Supposing that we start driving the instant the bomb goes off, because we “know”, (we have a clock with an alarm).  We drive away from the centre of the blast at 60 mph.

Now, the bomb’s blast is coming to us at 60mph and we’re driving away at 60mph.  When will the blast reach us?  Never.  That’s common sense.  No problem there.

Let’s say that the bomb has no real effect 240 miles away from the centre of the explosion.  That’s a four-hour radius.  We’re driving away from the bomb, so we drive for four hours.  That places us still an hour away from the bomb’s furthest reach, and since signals need an hour to reach us from that radius, and the bomb stopped having an effect, it never affected us.  We can’t see the result, or be affected by it, unless of course we drive back and see the devastation.  I’m not doing that.

For our scenario, this speed limit is a trick, we’ve slowed down the speed of any signal to human relatable speeds.  We couldn’t function if this was the case because, well for a start we couldn’t see.

If we cover ten times the distance, 600mph, it’s the same.  If we could drive that fast and scaled everything up to that speed, it’s exactly the same.

So, are you still with me at 6000mph?  That’s more than fast enough to reach New York from London in an hour, it should be clearer though that we don’t immediately know what is going on in New York if we live in London.  Still human scaled?

You should, hopefully be still with me at 6000mph, but what about 60,000 mph.  It’s no different, but are the scales getting large?

If we could travel at 60,000mph we could get to the moon in about four hours.  If that’s the speed-limit, then when we look at the moon we’re seeing it as it was four hours ago.  No problem there, because if the speed limit was 60mph it would be like looking at the moon from days ago.

Remember, there are a lot of things I’m ignoring because I want to focus of simultaneity; but there is no loss of accuracy in what I’m saying here, other effects are simply not part of the model and that actually doesn’t matter right now, it doesn’t make any difference.

So, our current speed limit is 60,000mph.  Signals from the moon take four hours, which means that anything that happens there hasn’t happened here for four hours.  For those four hours it cannot affect us.

Be aware, I’m leading you on in baby steps, but not down any garden path, this is real stuff, actually how the universe works.

The difference between our scenarios and the real world is only speed, light, which is the ultimate signal carrier, (because screw you quantum entanglement are you carrying a signal or not?), travels a lot faster than our slow speed limits.  A ridiculous amount faster.

This is how fast it goes, and it can’t go any faster because the universe has a speed limit.



Yes, somewhat over 6½ hundred million miles an hour.

Let’s do some simple sums.

Juno got into orbit around Jupiter the other day.  (Hurrah!  NASA).

The radio signal, (same speed as light) took 48 minutes to get back to Earth and tell us all that it had succeeded.  This means that until that signal came, that event, as far as we’re concerned, hadn’t happened.

(OK, I’m simplifying, Juno got into orbit and then confirmed it using on-board systems and then sent a signal back, but for our purposes we could have been looking through a high powered telescope and spent a little time observing and it would have been the same thing).

That lag, that seems so familiar, because it’s covered in the media all the time with little thought, is deeply profound, we cannot know what is happening “now” to Juno, we can only ever know what happened 48 minutes ago.  That is the closest that it is.  It is literally, universally 48 minutes away.  It now cannot be closer than that without journeying back to Earth.

So, sums.

48 minutes is 4/5th of an hour. (Look at a clock).

4/5th of 670,616,629, well, let’s not do that.  4/5th of something is the same as saying 0.8.

So 0.8 × 670,616,629 is about 536,493,303 miles

So, Jupiter about 536,493,303 miles away by our calculation.

Let’s see what NASA says.  Huh, NASA’s Jupiter page is down right now, so here’s a quote from instead.

How far is Jupiter from Earth?

Because both planets travel in an elliptical path around the sun, Jupiter‘s distance from Earth is constantly changing. When the two planets are at their closest point, the distance to Jupiter is only 365 million miles (588 million kilometres). From its closest point, Jupiter shines so brightly that even Venus dims in comparison. At its farthest, the gas giant lies 601 million miles (968 million km) away.”

(,; retrieved 8 July 2016)

Alright!  It seems that we have a clue.  It’s a bit further away, at the closest distance than our calculation, but certainly with some decent margin of error.  (I never expected to be spot on).

So yes, Jupiter is 48 minutes away, (did I get the 48 minutes right, you find out), and nothing there can affect us for at least that amount of time.

It should be clear now that simultaneity is a tricky thing, I’ve said more than once that “things can only be so simultaneous” and I hope it’s a bit clearer what that means.

We’ll cover what it means for something to be in your future, but my past, next time.


You can find many interesting things and follow the Juno mission at NASA has a vast array of public domain images and information about their missions and you can spend many happy hours finding out about the science they do.  (This isn’t an ad, I’m just saying, go there).

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