Can a time traveler prove himself using the blockchain?

[bitpop]

.

[Terk]

Yes. You need to transfer yourself back to 2009, mine a lot of the early coins and send 10 000 BTC of these early mined coins to the address in my signature. This will be enough proof for me.

[Remember remember the 5th of November]

If you are implying Satoshi is a time-traveler, I also think so as well. He could be traveling in time right now back to wherever he came from.

[PenAndPaper]

You can't go back in time. Only forward.   

[ajax3592]

You can't go back in time. Only forward.  

Yes   That's what a scientist friend told me, sad!

[PenAndPaper]

You can't go back in time. Only forward.  

Yes   That's what a scientist friend told me, sad!

Actually you don't have to be a scientist to realize that. It's based on philosophical arguments   . Scientists mostly agree anyway

[Minecache]

Time is a human concept. It represents nothing and it represents everything.

Bit like bitcoin.

[crazy_rabbit]

Well, theoretically you could go back in time, but you would need to build a time machine, and then you could only go back as far as the point where you turn the time machine one. So if satoshi didn't have one in 2009, then no- those coins are still locked up forever.

[forevernoob]

[Nancarrow]

To take the question 'seriously' for a moment: I think it could work something like this...

Time traveller from, say, 2026 takes a momentous event from that year, encodes it as a short string, e.g. "2026-10-31 Yellowstone Supervolcano Eruption, 16.2 million dead". They also take a blockhash from somewhen earlier, say the hash from block #38295874 on 26th Feb 2021 (I just banged my keypad for that block #, can't be bothered to calc a plausible number). They append that hash to the event message, and also append "This was the block hash for block #whatever on 2021-02-26 and I call myself Nancarrow on bitcointalk.org". They SHA-256 the whole lot. Then they travel back  to our time, carry out some trivial transaction and embed that SHA-256 as a message with the transaction. I'm not sure about that last bit, I seem to recall transactions do have some room for short strings, dunno if it's enough for a SHA-256 digest. Then of course they post a message here saying what they've done (after hacking my account, naturally, though I did think about messing with your heads for a while).

I may be overcomplicating how much info would need to be in the unhashed message, but I'm just trying to guard against all possibilities of someone crying foul about fudging the message. The other thing is, the time traveller would just need to say "take a look at the message in transaction xyz, I'll tell you all about it when I return to 2026". They should NOT explain what's actually in the unhashed message until 2026, if there's any reason to think humans could act to alter events so as to create a temporal paradox. While humans probably can't affect the supervolcano, they could easily enough act to prevent the future block hash being correct. The last thing the universe needs is a divide-by-zero error. So the time traveller couldn't claim credit until 2026.

If you're asking how a timetraveller could prove themselves NOW, I guess they'd have to come up with a series of events in our fairly short-term future, say the next couple of months, it would have to be in enough detail to prevent accusations of covering-by-vagueness, and it'd again have to be events that we could not reasonably act to prevent even with knowledge of them.

[bitpop]

Thanks

[DeathAndTaxes]

Yes someone could lookup in the blockchain the blockhash for a block that is the future relative to where the traveler is going.  It can be any block but making it a round significant block might be cooler.

Simply come back and tell people what it is.

For example:

I am a time traveler from the year 2097 the blockhash for block 300,000 is 0000000000000003fc5605e9e5427ce6caa48da17422b2a1eb769a54abc8c85f

Now you just need to wait for block 300,000 to confirm my story. BTW I may or may not be serious in the proclamation above.

[Jace]

Yes someone could lookup in the blockchain the blockhash for a block that is the future relative to where the traveler is going.  It can be any block but making it a round significant block might be cooler.

Simply come back and tell people what it is.

For example:

I am a time traveler from the year 2097 the blockhash for block 300,000 is 0000000000000003fc5605e9e5427ce6caa48da17422b2a1eb769a54abc8c85f

No you just need to wait for block 300,000 to confirm my story.

So now what happens if I include this hash earlier in the blockchain in some implicit way. For example, by sending a few satoshi's to the address for which the hash you mentioned is the private key.

This means the current and all subsequent block hashes will be different than what it would have been without you revealing your prediction. In a way that irriversibly depends on your prediction.

I see a problem here

[DeathAndTaxes]

A block hash isn't a hash of a private key.   It is the resulting random hash the miner will find that "solves" a block (solve being a block hash which is smaller than the target required by current difficulty).

Still if one was worried about a paradox you could instead say this:

I am a time traveler.  The following is a hash of a message which proves I am from the future.  I will reveal the message which can be hashed for verification after the event occurs.

cad26810362691dd6462a8bbb6606b08f360fa4086d60a2ac1dc86c10a12138e

BTW this is the hash for the message in the post above.  After block 300,000 I could reveal the message and one could hash the message to independently verify it was known prior to the event using a publicly available SHA-256 hash tool like:
http://www.xorbin.com/tools/sha256-hash-calculator

[blacksails]

You can't go back in time. Only forward.   

Well, it's possible to go back in time if you travel faster than light. To bad it's impossible (according to Einstein)!

[Bicknellski]

You can't go back in time. Only forward.  

There is no such thing as time.