Is Time Travel Possible In Our Universe?

foreign

it's a cold moonless night with a Mist

that hangs heavy in the air

as he turned across the road fog

swallows both the sound and headlights

of the oncoming car you see it too late

embrace yourself for impact

then out of nowhere an elderly stranger

shoves you out of Harm's Way is hit by

the car and ends up in a heap on the

tarmac

their life ends as yours is saved later

a police officer hands you an envelope

found in the pocket of the deceased it

is addressed to you you open this

envelope and find a note with two words

scribbled on it

simply reads

study Physics whoever wrote this note

saved your life at the expense of theirs

so it only seems fair you follow their

advice

decades later you become a much

celebrated physics professor your

specialist subject Albert Einstein's

theories of Relativity you've always had

a hunch that time travel is possible and

one day finally you crack it at the

world's very first time machine is set

buzzing before you only then does the

penny drop how would you never realize

before you now have the power to go

anywhere and any when but you know

exactly what you have to do you take the

letter you've kept all these years out

of its frame on the wall place it back

inside its original envelope and put the

envelope in your pocket stepping into

your time machine you set the controls

to take you back to a cold moonless

Misty night arriving just in time to

push your younger self out of the path

of the on-rushing car

you die on the roadside

seems simple enough

but the real Joy of time travel stories

like this one comes once you begin to

scratch beneath the surface and some

incredibly profound questions begin to

emerge

first of all who wrote the letter

the older version of you simply takes

the letter they'd already been given as

a teenager back in time the letter is a

seemingly creatorless entity stuck in a

Time Loop this is the bootstrap paradox

secondly do these time Loops keep on

repeating you save your teenage self so

they grow up to travel back in time to

save their teenage self who grows up to

travel back in time and so on you are

stuck in a Relentless cycle of living

and dying but the letter isn't

does it just keep getting older and more

worn and tattered

this is the restoration paradox

and whose idea was it to study Physics

anyway the notion seems to appear out of

nowhere a thought with no origin this is

the ex-niello Paradox and if events like

this can actually happen then it also

appears you have no free will no choices

in life you are always going to invent

the time machine and had absolutely no

option to do otherwise it

to happen had always happened if you

don't invent a time machine then you

can't save your teenage self and you

yourself would therefore die as a

teenager there is something in your

future that's firmly fixed this is the

predestination paradox

and finally what if you change your mind

unfortunately for your older self this

is not an option you can't get cold feet

when you arrive and that the younger you

get hit by the car how could you be

there to have second thoughts in the

first place

this is the auto infanticide Paradox it

is impossible to kill a younger version

of you even through the act of not doing

something

and so not quite such a simple story

welcome to the weird and wonderful world

of time travel

but of course traveling freely through

time is impossible you might say you

can't simply visit yesterday or Rush

head long through millennia

and yet this too is not quite so

straightforward despite its Myriad

impracticalities there are slivers of

possibility lurking at the edge of

physics temporal loopholes lying just

Out Of Reach

and so the question arises if time

travel were to be possible just how

could we do it

[Music]

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educational content on YouTube

the Sun beats down as the distinctive

whooping barks of howler monkeys Echo

around the humid swamps the current in

the muddy winding river is so strong

that you don't even have to paddle your

canoe you just sit back and take in the

sights and sounds as you're carried

along

Jack Finney arguably one of the finest

proponents of time travel fiction

compared our experience of time to a

river like this one it seems like we're

relentlessly ferried Downstream from the

past to the future we have no need to

propel ourselves but slowing down

speeding up or turning around and

heading back Upstream doesn't seem

possible either but what happens to the

parts of the river that we've left

behind or in other words what is

yesterday go

it certainly seems as if it just

disappears yet making the same argument

about an actual River would seem

ludicrous you're unlikely to accept that

the riverbed is torn up and mysteriously

vanishes just because you've disappeared

around the next bend the Upstream parts

of the river are still there even if you

aren't in the same way it seems as if

tomorrow isn't real until it is that

somehow it magically appears once the

curtain falls on today but that would be

like new water springing up to make the

river of time longer only once you

approach where would it come from

and so over the years scientists have

revealed that time really is like that

River with its length already laid out

in its entirety from its source high in

the foothills of the Big Bang to its

Estuary at the universe's eventual

demise the past present and future

existing alongside one another your

great great grandchildren every bit as

real as you are now your great great

grandparents still alive and well

frolicking in the swells Upstream in the

vast River of time

philosophers know this idea as

eternalism it's the opposite of

presentism which argues that only now

exists and that the past is gone and the

future yet to emerge debates between

eternalist and presentist philosophers

have raged since the days of ancient

Greece indeed the 4th Century