Think about the idea of "here". I am here. You, while reading this, can truly say "I am here", even though your "here" is different to mine.

On the block universe model, talk about the "present" or "now" works just like talk of "here".

Remember last week when you said...

How can this be?

The block has four dimensions: three spatial dimensions — say length, height and width — plus a fourth temporal dimension, or time. Or let's make it easier, by visualising the block model of our world as a three-dimensional rectangle, or cuboid.

Two of that cuboid's dimensions (let's say height and width) represent two of the universe's three spatial dimensions.

Leave out the third spatial dimension in the above diagram (the length) —and replace it with time. At one end of the cuboid is the big bang. At the other is th...

Bearing this in mind, it is possible to see how to make sense of the idea of past and future.

Just as on this model “now” picks out whatever time I happen to be located at, “past” picks out any time (or events at those times) that are earlier than my location, and “future”...

We’ll get out of our time machine and start walking around. We’ll breathe the air and chat to people.

Obviously, this will have effects on the time we travel to. We’ll tread on ants; we’ll talk to people from that time; we’ll pat horses, and feed donkeys and so on.

We’ll act, ...

If time is just another dimension, a lot like the spatial dimensions, does that mean we can travel in time?

The short answer is yes.

Of course, things are way more complicated than that. Travelling in time is clearly much more difficu...

No.

That would create a contradiction, and there are no contradictions.

Remember, on the block universe model, the past is no different than the future or the present.

Everything is relative: ...

Nothing a time traveller does changes anything in the block. Instead, what the traveller does at any time makes that time, and later times, the way they are.

That means that we know that some things we attempt to do in the past, fail. We know that Hitler r...

We already know that travelling very fast will result in time dilation, so we know it's possible to travel into the future just by travelling very fast.

We can travel quite a way into the future if we can travel at some reasonable percentage of the speed of light. ...

Let's recap.

What we do tomorrow makes tomorrow the way it is, and the way it always has been. What we do in the past makes the past time the way it is, and always has been.

If we travel to the past, we are part of the past. Importantly, ...

Since we are always located wherever we are (that's trivially true), everyone is located in the present, just as everyone is located at the place they call “here”.

According to the block universe view, time or temporal relations of “earlier than” and “later than”