At the moment the only way to buy most alt coins is using bitcoins, so yes the real world dollar/pound/euro value is related directly to the price of bitcoin.
Hi JayBex. Welcome. Yes. I agree to an extent with the statement above "that the price of an alt-coin is related to the price of a BTC" ... except for a few alts that have separate USD markets (or trade directly with other national currencies). Cryptsy has 10 active USD markets. Hopefully, pretty soon, DGB will also have a dedicated market.
However, just because the price of an alt-coin is determined through an exchange rate with BTC, doesn't mean that the 2 values are connected in a causal relationship with price movement. BTC price could decline while DGB rises, or they could both go up on the same day, or both go down on the same day. The market exchange rate isn't fixed or pegged to BTC for most alt-coins (although many alt-coins have very predictable exchange-ranges and relationships with BTC). So the relationship between the two is correlative not causal.
Hi mate, I see i think i get it, i was confused by thinking if the price of btc doubled then the price of digibyte would halve to 35 sat. So the dgb price would stay where it is at 70 sat? Would the price naturally decrease to 35 sat if there is a currency exchange market for dgb?
You're asking interesting, but also complicated questions that don't have easy answers. Different people trade differently. Some are interested in their BTC balance. They will have different reactions to changes in BTC price. Others are interested in their alt-coin balances, so they will also have different reactions.
Here's my best short answer ... if the price of DGB is currently X ... and somehow the price of BTC doubled ... it wouldn't be like the price of DGB would automatically be (1/2)X. There would be downward pressure on the exchange value of DGB because people would want to capitalize on the higher exchange value, so there would likely be an increase in sell orders. But, it wouldn't by default (or automatically) halve the value of DGB. Other coins ... like LTC ... tend to be more closely coupled with a perceived value in relation to BTC price. LTC is often traded between 8% and 10% the value of BTC. So, if the price of BTC doubled, it's likely that there would be strong buy pressure for the price of LTC to also increase to match.
My best advice is to pick a couple of different alt-coins, (no more than 2 at a time), and watch their price movements, volume, etc., in relation to BTC over a couple of weeks.
http://coinmarketcap.com/ is a good place compare them easily.
And, I don't think that a DGB exchange would have negative impact on the price. In fact, I believe the opposite - it would make the DGB economy more valuable and accessible.