10 REM LOOKBACK.BAS - Lookback Time 20 REM by Thomas A. Weil 30 RM = 3700 / 2.7-1 40 INPUT "Will you enter the (A)ge of the universe or the (H)ubble parameter"; AH$ 50 IF AH$ = "H" OR AH$ = "h" GOTO 90 60 IF AH$ <> "A" AND AH$ <> "a" GOTO 40 70 INPUT "Enter age of the universe NOW in billions of years"; TN 80 TN = TN * 1E+09: GOTO 110 90 INPUT "Enter Hubble parameter in km/sec/Mpc"; HN 100 TN = (2 / 3) / (HN / 9.7781E+11) 110 INPUT "Enter (T)ime THEN or (R)edshift of the light we see NOW"; TR$ 120 IF TR$ = "R" OR TR$ = "r" GOTO 190 130 IF TR$ <> "T" AND TR$ <> "t" GOTO 110 140 INPUT "Enter age of the universe THEN in billions of years"; TT 150 TT = TT * 1E+09: SC = (TN / TT) ^ (2 / 3): RS = SC - 1: IF RS < RM GOTO 230 160 SM = RM + 1: TM = TN / (SM ^ 1.5) 170 PRINT : PRINT USING "You can't look back to a time earlier than ####### years"; TM 180 PRINT : GOTO 110 190 INPUT "Enter redshift value for the light we see NOW"; RS 200 SC = RS + 1: TT = TN / (SC ^ 1.5): IF RS < RM GOTO 230 210 PRINT : PRINT USING "Redshift value too large; nothing at redshift beyond ##### can be seen"; RM 220 GOTO 160 230 PRINT : PRINT USING "Age of the universe NOW = ###.#### billion years"; TN / 1E+09 240 PRINT USING "Age of the universe THEN = ###.#### billion years"; TT / 1E+09 250 TV = TN - TT 260 PRINT USING "Light travel time = ###.#### billion years"; TV / 1E+09 270 SC = (TN / TT) ^ (2 / 3) 280 PRINT USING "Scale of the universe NOW versus THEN = ####.###"; SC 290 RS = SC - 1 300 PRINT USING "Redshift of the light we see NOW = ####.###"; RS 310 DT = 3 * TT * ((TN / TT) ^ (1 / 3) - 1) 320 PRINT USING "Distance of object THEN = ##.### billion light-years"; DT / 1E+09 330 DN = DT * SC 340 PRINT USING "Distance of object NOW = ##.### billion light-years"; DN / 1E+09 350 ST = 2 * ((TN / TT) ^ (1 / 3) - 1) 360 PRINT USING "Speed away from us THEN = ##.### x speed of light"; ST 370 SN = 2 * ((TN / TT) ^ (1 / 3) - 1) / (TN / TT) ^ (1 / 3) 380 PRINT USING "Speed away from us NOW = ##.### x speed of light"; SN 390 HT = (2 / 3) / TT * 9.7781E+11 400 PRINT USING "Hubble parameter THEN = #######.# km/sec/megaparsec"; HT 410 HN = (2 / 3) / TN * 9.7781E+11 420 PRINT USING "Hubble parameter NOW = #######.# km/sec/megaparsec"; HN 500 REM ======================== 510 REM FROM "ASTRONOMICAL 520 REM COMPUTING," SKY & TELE- 530 REM SCOPE, SEPTEMBER 1997 540 REM ======================== 550 END